Home About us Contact
|
Home About us Contact | ||
|
|
||
Standard Solutions (standard + solution)
Selected AbstractsMulti-component analysis: blind extraction of pure components mass spectra using sparse component analysisJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2009Ivica Kopriva Abstract The paper presents sparse component analysis (SCA)-based blind decomposition of the mixtures of mass spectra into pure components, wherein the number of mixtures is less than number of pure components. Standard solutions of the related blind source separation (BSS) problem that are published in the open literature require the number of mixtures to be greater than or equal to the unknown number of pure components. Specifically, we have demonstrated experimentally the capability of the SCA to blindly extract five pure components mass spectra from two mixtures only. Two approaches to SCA are tested: the first one based on ,1 norm minimization implemented through linear programming and the second one implemented through multilayer hierarchical alternating least square nonnegative matrix factorization with sparseness constraints imposed on pure components spectra. In contrast to many existing blind decomposition methods no a priori information about the number of pure components is required. It is estimated from the mixtures using robust data clustering algorithm together with pure components concentration matrix. Proposed methodology can be implemented as a part of software packages used for the analysis of mass spectra and identification of chemical compounds. Copyright © 2009 John Wiley & Sons, Ltd. [source] Nitrogen purity influences the occurrence of As+ ions in high-performance liquid chromatography/electrospray ionization mass spectrometric analysis of four common arsenosugarsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2003Doris Kuehnelt High-performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC/ESI-MS) can provide both elemental and molecular information and, therefore, is a very useful tool for the identification of arsenic compounds. When a method for the identification of four arsenosugars was employed in our laboratory with an HPLC/ESI-MS system equipped with a Whatman model 75-72 nitrogen generator, a signal at m/z 75 (As+) could not be observed. When the HPLC/ESI-MS system was operated with nitrogen 5.0 (nitrogen of a purity of at least 99.999%) all four arsenosugars gave a signal at m/z 75. Because of this observation the influence of the quality of the nitrogen drying gas on the fragmentation of the four arsenosugars was systematically investigated. Standard solutions containing the four arsenosugars (0.5 ng As each) were separated on an anion-exchange column and detected with ESI-MS in the positive ion mode by monitoring the signals for [M+H]+, m/z 237, 91, and 75. Nitrogen with defined oxygen concentrations was used as drying gas. The purity of the nitrogen ranged from 99 to 99.999% (10,400 to 10 ppm oxygen impurity). The nitrogen with 99% purity gave no signal at m/z 75, but signals were obtained at m/z 91, 237, and for [M+H]+. When higher purity nitrogen (99.9%) was used, a signal was obtained at m/z 75, which accounted for 0.8,1.1% (depending on the kind of arsenosugar) of the sum of the signals for m/z 75, 91, 237 and [M+H]+. As the level of oxygen in the nitrogen decreased, the m/z 75 signal increased to 2.0,3.1%. This was accompanied by a concomitant decrease in the m/z 91 signal from 5.2,6.6% to 0.7,1.5%, whereas the signals for [M+H]+ and m/z 237 were essentially unchanged. Signals at m/z 75 with intensities comparable with those observed for the 99.9% pure nitrogen were also obtained for all the arsenosugars when the HPLC/ESI-MS system was operated with a Domnick Hunter Nitrox UHPLCMS18 nitrogen generator. Dimethylarsinic acid, arsenobetaine, trimethylarsine oxide, arsenocholine and the tetramethylarsonium cation also gave no signal at m/z 75 when they were analyzed with the Whatman model 75-72 nitrogen generator, but clear signals at m/z 75 were observed with the Domnick Hunter Nitrox UHPLCMS18 nitrogen generator. A nitrogen quality of at least 99.9% is required to obtain elemental information (m/z 75) when arsenic compounds are investigated by HPLC/ESI-MS. Molecular and elemental information from one chromatographic run is a valuable tool for the characterization of unknown arsenic compounds. Copyright © 2003 John Wiley & Sons, Ltd. [source] 13C/12C Ratios of endogenous urinary steroids investigated for doping control purposesDRUG TESTING AND ANALYSIS, Issue 2 2009Thomas Piper Abstract In order to detect the misuse of endogenous anabolic steroids such as testosterone by athletes a total of n = 1734 suspicious urine samples were investigated by gas chromatography/combustion/isotope ratio mass spectrometry throughout the years 2005, 2006 and 2007. The 13C/12C ratio of a target substance (androsterone, a testosterone metabolite) was compared to the 13C/12C ratio of an endogenous reference compound (11,-hydroxyandrosterone). N = 1340 samples were investigated due to elevated testosterone/epitestosterone ratios, with n = 87 (6.5%) exceptional findings regarding their isotopic ratios. An additional n = 164 samples were investigated because of elevated dehydroepiandrosterone concentrations, with n = 2 (1.2%) exceptional findings. The remainder were subjected to isotope ratio analysis because of elevated androsterone levels or because this was requested by sports federations. Significant differences between female and male samples were found for the 13C/12C ratios of androsterone and 11,-hydroxyandrosterone but not for samples taken in or out of competition. A further n = 645 samples originating from other World Anti-Doping Agency accredited laboratories, mainly throughout Europe as well as South America, South Africa and Southeast Asia, were investigated. The 13C/12C ratios of the urinary steroids differ significantly for each geographical region, reflecting the dietary status of the individuals. The system stability over time has been tested by repeated injections of a standard solution and repeated processing of frozen stored blank urine. Despite a drift over time in absolute 13C/12C ratios, no significant change in the difference of 13C/12C (11,-hydroxyandrosterone) minus 13C/12C (androsterone) could be observed. Copyright © 2009 John Wiley & Sons, Ltd. Copyright © 2009 John Wiley & Sons, Ltd. [source] Simultaneous Determination of Copper and Bismuth by Anodic Stripping Voltammetry Using H-Point Standard Addition Method with Simultaneous Addition of AnalytesELECTROANALYSIS, Issue 17 2005Esmaeil Shams Abstract Simultaneous determination of bismuth and copper by anodic stripping voltammetry using H-point standard addition method (HPSAM) with simultaneous addition of analytes is described. The effect of various parameters including acid concentration, accumulation time, accumulation potential and concentration ratio of analytes in the standard solution on the sensitivity and accuracy of method were investigated. The results of applying the H-point standard addition method showed that Cu2+ and Bi3+ could be determined simultaneously with the concentration ratios of Cu2+ to Bi3+ varying from 1,:,15 to 16,:,1 in the mixed sample. The method was successfully applied to the simultaneous determination of copper and bismuth in some synthetic mixtures. [source] Combined use of supported liquid membrane and solid-phase extraction to enhance selectivity and sensitivity in capillary electrophoresis for the determination of ochratoxin A in wineELECTROPHORESIS, Issue 7 2008Sara Almeda Abstract This paper proposes a novel strategy to enhance selectivity and sensitivity in CE, using supported liquid membrane (SLM) and off-line SPE simultaneously. The determination of ochratoxin A (OA) in wine has been used to demonstrate the potential of this methodology. In the SLM step, the donor phase (either a 20,mL volume of a standard solution at pH,1 or a wine sample at pH,8) was placed in a vial, where a micromembrane extraction unit accommodating the acceptor phase (1,mL water, pH,11) in its lumen was immersed. The SLM was constructed by impregnating a porous Fluoropore Teflon (PTFE) membrane with a water-immiscible organic solvent (octanol). In the off-line SPE step, the nonpolar sorbent (C-18, 4,mg) selectively retained the target ochratoxin, enabling small volumes of acceptor phase (1,mL) to be introduced. The captured analytes were eluted in a small volume of methanol (0.1,mL). This procedure resulted in sample cleanup and concentration enhancement. The method was evaluated for accuracy and precision, and its RSD found to be 5%. The LODs for OA in the standard solutions and wine samples were 0.5 and 30,,g/L, respectively. The results obtained demonstrate that SLM combined with off-line is a good alternative to the use of immunoaffinity columns prior to CE analysis. [source] Does the standard intravenous solution of fentanyl (50 µg/mL) administered intranasally have analgesic efficacy?EMERGENCY MEDICINE AUSTRALASIA, Issue 1 2010Dianne Crellin Abstract Background: Intranasal (IN) fentanyl provides rapid and powerful non-parenteral analgesia in the ED. A concentrated solution of fentanyl (300 µg/mL) has been used in prior trials, yet many ED use the standard solution at a concentration of 50 µg/mL, which is widely available and of low cost. We set out to determine if this lower concentration of fentanyl is also efficacious. Methods: Prospective audit in children aged 5,18 years presenting with upper limb injuries. Patients received IN fentanyl (50 µg/mL) at 1.5 µg/kg. Patient assessed pain scores were collected 5, 10, 20, 30 and 60 min following IN fentanyl administration using a visual analogue scale or Bieri Faces , Revised scale. Parental scores were used if patients were unable to provide a score. Results: Of the 59 eligible patients, 36 were enrolled; median age was 6.8 years (range 5,15 years), and 89% (32/36) ultimately required fracture reduction. Median first dose of IN fentanyl was 1.4 µg/kg. Median pain scores dropped from 7 (interquartile range 5,10) pre-fentanyl to 5 (interquartile range 4,8) at 5 min and 2 (interquartile range 1,4) at 30 and 60 min. A total of 21 (58%) children did not require further analgesia in the ED. There were no adverse events. Conclusions: Standard i.v. concentration IN fentanyl (50 µg/mL) appears to have analgesic efficacy in children with upper limb injuries. [source] A new lightning protection system for wind turbines using two ring-shaped electrodesIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 3 2006Yasuda Yoh Member Abstract Wind turbines are often struck by lightning because of their special shape, their tall structure and their being placed in the open air. Besides seriously damaging the blades, lightning results in accidents in which low-voltage and control circuit breakdowns frequently occur in many wind farms worldwide. Although some reports, such as IEC TR61400-24 and NREL SR-500-31115, have indicated a methodology for protection against such accidents, a standard solution to these problems remains to be established. The author, focusing on a method for protection of low-voltage and control circuits in a wind tower, proposed a new lightning protection system with two ring-shaped electrodes attached to the wind turbine. The proposed system has two ring-shaped electrodes of several meters diameter, one vertically attached to the nose cone and the other laterally placed at the top of the wind tower lying just below the nacelle. The pair of rings is arranged with a narrow gap of no more than 1 m in order to avoid mechanical friction during rotation of the blades and the nacelle's circling. When lightning strikes a blade, the current reaches the upper ring from a receptor through a conductive wire. Then, the electric field between the two rings becomes high and finally sparks over and the lightning current flows downwards. The current propagates along the lower ring and the grounding wire, which is arranged outside of the wind tower rather than inside, and is safely led to a grounding electrode placed far enough away from the tower's grounding system. In this paper, the author describes a basic experiment using a 1/100 downsized model, and also discusses the concept behind the present system. The result of the downsized experiment provides evidence of an effective advantage for lightning protection. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Antioxidant properties of methanolic extracts from different parts of Sclerocarya birreaINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 5 2008Abdalbasit A. Mariod Summary The methanolic extracts from Sclerocarya birrea leaves (SCL), roots (SCR), barks (SCB), and kernel oil cake (SCK) were examined for radical scavenging capacities and antioxidant activities. The total phenolics of the extracts was determined spectrophotometrically according to the Folin-Ciocalteau method using gallic acid as standard solution. The total phenolic compounds were found as 304.5, 367.5, 593, 148.0 and 258.0 mg g -1 of dry product, respectively. The extracts of SCL, SCR, SCB and SCK were markedly effective in inhibiting the oxidation of linoleic acid and subsequent bleaching of ,-carotene in comparison with the control. Based on oxidation of ,-carotene/linoleic acid, the SCK extract is the most effective followed by SCR, SCL and SCB extract. The antioxidant activity determined by the DPPH (1,1-diphenyl-,-picrylhydrazyl) method revealed that the SCK extract had the highest antioxidant activity on DPPH free radicals followed by SCB, SCR and SCL extracts. The effect of different extracts on the oxidative stability of sunflower oil at 70 °C was tested in the dark and compared with BHA. The oil peroxide values (PVs) were generally lower with the addition of extract in comparison to a control. [source] Rapid in vitro conversion of fosphenytoin into phenytoin in sera of patients with liver disease: Role of alkaline phosphatase ,JOURNAL OF CLINICAL LABORATORY ANALYSIS, Issue 5 2001Amitava Dasgupta Abstract Fosphenytoin, a phosphate ester pro drug of phenytoin, also cross-reacts with the fluorescence polarization immunoassay (FPIA) for phenytoin. We measured fosphenytoin concentrations using the FPIA kit and TDx analyzer. We prepared serum pools from normal volunteers and patients with liver disease. None of them received either fosphenytoin or phenytoin. Fosphenytoin standard solution (1 mg/ml) was prepared in water. We supplemented aliquots of normal and liver pools with known amounts of fosphenytoin and measured the concentrations at different time intervals. The conversion of fosphenytoin to phenytoin was slow in sera with normal alkaline phosphatase activities. The conversion was rapid in sera collected from patients with liver disease who also had high alkaline phosphatase activities. The observed concentrations were close to target concentrations within 0,2 min of supplementation with fosphenytoin. Surprisingly, the observed concentration then started to decline slightly but significantly with longer incubation time. In contrast, the observed concentration increased steadily in serum with normal alkaline phosphatase activity. For example, in the normal pool supplemented with 15.0 ,g/ml fosphenytoin (as the phenytoin equivalent), the observed concentrations were 6.9, 7.3, 7.7, 8.3, and 9.8 ,g/ml at 0,2, 10, 20, 30, and 60 min, respectively. However, in a serum pool prepared from patients with liver disease and supplemented with 15.0 ,g/ml of fosphenytoin (alkaline phosphatase: 2547 U/l), the observed phenytoin concentrations were 12.9, 12.1, 11.0, 10.7, and 10.7 ,g/ml at 0,2, 10, 20, 30, and 60 min, respectively. When we added alkaline phosphatase to the normal serum pool, we observed rapid conversion of fosphenytoin into phenytoin within 10 min, but the concentrations then declined with longer incubation time. However, when we repeated the experiment with protein-free ultrafiltrate, we observed rapid conversion of fosphenytoin to phenytoin, but the concentration did not decline with longer incubation time. J. Clin. Lab. Anal. 15:244,250, 2001. © 2001 Wiley-Liss, Inc. [source] ORGANIC ACIDS PROFILE IN TOMATO JUICE BY HPLC WITH UV DETECTIONJOURNAL OF FOOD QUALITY, Issue 1 2007OMBRETTA MARCONI ABSTRACT A simple method was developed to determine 10 organic acids simultaneously in tomato products using reverse-phase high performance liquid chromatography (HPLC) column with the diode array detector set at 210 nm. After centrifugation and filtration, the samples were passed through to an anion exchange resin and the organic acids were released using 0.1 N HCl. The chromatographic separation was achieved with isocratic analysis in a 20-min run. The method was reliable and sensitive. The coefficient of determination of the standard calibration curve is 0.9925 , r2 , 0.9999 and the limit of detection ranged from 0.08 to 6.00 mg/kg for trans -aconitic acid and acetic acid, respectively. The limit of quantification ranged from 0.19 to 15.18 mg/kg for trans-aconitic and acetic acid, respectively. To establish the efficiency of the anion resin the procedure was applied to a standard solution of a mixture of organic acids. The organic acids recovery ranged from 87.0% ± 1.9 for citramalic acid to 109.9% ± 5.2 for fumaric acid. [source] Chemistry of ,-hydroxymethylserine: problems and solutions,JOURNAL OF PEPTIDE SCIENCE, Issue 11 2008Marcin Stasiak Abstract Further improvements related to the synthesis of peptides containing HmS are presented. Efficient synthetic protocols have been developed to synthesize "difficult" sequences containing a C -terminal HmS residue, MeA,HmS or consecutive HmS. Preparative methods for orthogonal N - and/or C -protected HmS(Ipr) derivatives are described. Their compatibility with standard solution or solid-phase peptide chemistry protocols allows synthetic flexibility toward HmS-containing peptides. In the synthesis of the sterically hindered dipeptides with the C -terminal HmS(Ipr) residue, HATU proves the highest efficiency, as compared with the fluoride and PyBroP/DMAP coupling methods. The HATU method also outperforms the fluoride activation in the solid-phase assembly of HmS homosequence. Specific protocols are described to overcome an undesired cyclization to diketopiperazines that occurs during the removal of Fmoc from dipeptides with the C -terminal HmS(Ipr) or HmS residues, thus precluding their C , N elongation. The successful protocols involve: (i) the 2 + 1 condensation using mixed anhydride activation yielding the desired product with the highest optical integrity or (ii) use of the 2-chlorotrityl resin as a solid support sterically suppressing the undesired cleavage due to diketopiperazine formation. The latter approach allows the mild conditions of peptide cleavage from solid support, preserving the isopropylidene protection and minimizing the undesired N , O -acyl migration that was observed under prolonged acid treatment used for cleaving the HmS peptide from the Wang resin. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source] The Effect of Topical Epinephrine on Peripheral Nerve Conduction,,§THE LARYNGOSCOPE, Issue 10 2002Quintessa Miller MD Abstract Objective/Hypothesis The aim of the study was to determine the effect of direct application of epinephrine solution on peripheral nerve conduction latency and amplitude. It was hypothesized that epinephrine does not cause neurapraxia when a standard (1:10,000) solution is applied topically. Study Design Eleven animals were divided into two groups of five and six. Group I had their left sciatic nerves and group II had their right sciatic nerves treated with epinephrine-soaked patties. The contralateral nerves of each group served as controls. Methods Nerve conduction studies were performed at baseline and immediately, at 1 minute, and at 5 minutes after patty application. Results Latency was found to increase above baseline immediately after patty application (P = .003) for the epinephrine-treated and saline-treated groups. Furthermore, the amplitude at 5 minutes after patty application increased from baseline (P = .009) for both groups. These observed differences were below what is considered to be clinically significant. Conclusion Topical epinephrine at a standard solution (1:10,000) does not lead to clinically significant nerve conduction abnormalities. [source] Analytical sensitivity of arsenobetaine on atomic spectrometric analysis and the purity of synthetic arsenobetaine,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2006T. Narukawa Abstract Arsenobetaine is one of the main organoarsenic compounds that exist in living organisms. Determination errors in total arsenic analyses for organoarsenic compounds occur because analytical sensitivities depend upon the chemical forms of the compounds. However, information on the analytical sensitivity of arsenobetaine by ICP-MS and ICP-AES and the purity of commercially available arsenobetaine standards is lacking. BCR CRM 626 (arsenobetaine solution) is a certified reference material from IRMM with a certified concentration of arsenobetaine. The sensitivity and behavior of arsenobetaine on ICP-MS and ICP-AES were investigated using the BCR arsenobetaine. The analytical sensitivity and behavior of arsenobetaine using ICP-MS and ICP-AES were also investigated using a commercially available synthetic arsenobetaine, and were compared with results for BCR-AB based on a Japan calibration service system (JCSS) arsenic standard solution. In the results, arsenic determined directly in arsenobetaine showed about 15% greater sensitivity in analysis by ICP-MS and ICP-AES than did inorganic (JCSS) arsenic. Copyright © 2006 John Wiley & Sons, Ltd. [source] HPLC-fluorescence assay for measuring mosapride in small volumes of rat plasmaBIOMEDICAL CHROMATOGRAPHY, Issue 3 2010Ching-Ling Cheng Abstract A simple and sensitive HPLC-fluorescence assay was developed for the determination of a gastroprokinetic agent mosapride in small volumes of rat plasma. Samples (50 ,L) were treated with 200 ,L of the internal standard solution (cisapride, 0.1 ,g/mL in acetonitrile). Chromatographic separation was achieved on a C18 column by gradient elution with the mobile phase of acetonitrile-water containing 20 mM potassium dihydrogen phosphate, at a flow rate of 1 mL/min. Fluorescence was measured with excitation and emission set at 315 and 354 nm, respectively. The retention time was about 16 min for cisapride and 20 min for mosapride. No endogenous substances were found to interfere. The calibration curve was linear from 0.015 to 10 ,g/mL. The lower limit of quantification was 0.015 ,g/mL. The intra- and inter-day precision expressed as relative standard deviation did not exceed 7.7%, and the accuracy was within 4.7% deviation of the nominal concentration. The method was used successfully to investigate the disposition kinetics of mosapride in rats. Copyright © 2009 John Wiley & Sons, Ltd. [source] Simultaneous determination of methylephedrine and pseudoephedrine in human urine by CE with electrochemiluminescence detection and its application to pharmacokeineticsBIOMEDICAL CHROMATOGRAPHY, Issue 11 2009Yan-Ming Liu Abstract A novel method for the determination of ephedra alkaloids (methylephedrine and pseudoephedrine) was developed by electrophoresis capillary (CE) separation and electrochemiluminesence detection (ECL). The use of ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, BMIMBF4) improved the detection sensitivity markedly. The conditions for CE separation, ECL detection and effect of ionic liquid were investigated in detail. The two ephedra alkaloids with very similar structures were well separated and detected under the optimum conditions. The limits of detection (signal-to-noise ratio = 3) in standard solution were 1.8 × 10,8 mol/L for methylephedrine (ME) and 9.2 × 10,9 mol/L for pseudoephedrine (PSE). The limits of quantitation (signal-to-noise ratio = 10) in human urine samples were 2.6 × 10,7 mol/L for ME and 3.6 × 10,7 mol/L for PSE. The recoveries of two alkaloids at three different concentration levels in human urine samples were between 81.7 and 105.0%. The proposed method was successfully applied to the determination of ME and PSE in human urine and the monitoring of pharmacokinetics for PSE. The proposed method has potential in therapeutic drug monitoring and clinical analysis. Copyright © 2009 John Wiley & Sons, Ltd. [source] Investigation of the Effect of Different Glassy Carbon Materials on the Performance of Prussian Blue Based Sensors for Hydrogen PeroxideELECTROANALYSIS, Issue 3 2003Francesco Ricci Abstract Three different kinds of glassy carbon (GC-R, GC-K, GC-G) were equally pretreated, further modified with electrochemically deposited Prussian Blue and used as sensors for hydrogen peroxide at an applied potential of ,50,mV (vs. Ag|AgCl). Their performance was evaluated with respect to the following parameters: the coverage and electrochemistry of the electrodeposited Prussian Blue, the sensitivity and the lower limit of detection for hydrogen peroxide, and the operational stability of the sensors. GC-R showed the best behavior concerning the surface coverage and the operational stability of the electrodeposited Prussian Blue. For this electrode the sensitivity for hydrogen peroxide (10,,M) was 0.25,A/M cm2 and the detection limit was 0.1,,M. Scanning electron microscopy was used to study the surfaces of the three electrodes before and after the electrodeposition of Prussian Blue and to search for the reason for the three different behaviors between the different glassy carbon materials. The Prussian Blue modified GC-R was also used for the construction of a glucose biosensor based on immobilizing glucose oxidase in Nafion membranes on top of electrodeposited Prussian Blue layer. The operational stability of the glucose biosensors was studied in the flow injection mode at an applied potential of ,50,mV (vs. Ag|AgCl) and alternatively injecting standard solutions of hydrogen peroxide (10,,M) and glucose (1,mM) for 3,h. For the GC-R based biosensor a 2.8% decrease of the initial glucose response was observed. [source] Capillary electrophoretic separation of biologically active amines and acids using nanoparticle-coated capillariesELECTROPHORESIS, Issue 9 2008Yu-Fen Huang Abstract This manuscript describes dynamic coating of capillaries with poly(L -lysine) (PLL) and silica nanoparticles (SiO2 NPs) and use of the as-prepared capillaries for the separation of biogenic amines and acids by CE in conjunction with LIF detection. The directions of EOF are controlled by varying the outmost layer of the capillaries with PLL and SiO2 NPs, respectively. Over the pH range 3.0,5.0, the (PLL,SiO2NP)n,PLL capillaries have an EOF toward the anodic end and are more suitable for the separation of acids with respect to speed, while the (PLL,SiO2NP)n capillaries have an EOF toward the cathodic end and are more suitable for the separation of biogenic amines regarding speed and sensitivity. The separations of standard solutions containing five amines and two acids by CE with LIF detection using (PLL,SiO2NP)2,PLL and (PLL,SiO2NP)3 capillaries were accomplished within 10 and 7,min, providing plate numbers of 3.8 and 5.0×104,plates/m for 5-hydroxytryptamine (5-HT), respectively. The LODs for 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) are 32 and 2,nM and 0.2 and 1.5,nM when using the (PLL,SiO2NP)2,PLL and (PLL,SiO2NP)3 capillaries, respectively. Identification and quantification of 5-HIAA, homovanillic acid, and DL -vanillomandelic acid in urine samples from a male before and after drinking green tea were tested to validate practicality of the present approach. The results show that the (PLL,SiO2NP)2,PLL capillary provides greater resolving power, while the (PLL,SiO2NP)3 capillary provides better sensitivity, higher efficiency, and longer durability for the separation of the amines and acids. [source] Combined use of supported liquid membrane and solid-phase extraction to enhance selectivity and sensitivity in capillary electrophoresis for the determination of ochratoxin A in wineELECTROPHORESIS, Issue 7 2008Sara Almeda Abstract This paper proposes a novel strategy to enhance selectivity and sensitivity in CE, using supported liquid membrane (SLM) and off-line SPE simultaneously. The determination of ochratoxin A (OA) in wine has been used to demonstrate the potential of this methodology. In the SLM step, the donor phase (either a 20,mL volume of a standard solution at pH,1 or a wine sample at pH,8) was placed in a vial, where a micromembrane extraction unit accommodating the acceptor phase (1,mL water, pH,11) in its lumen was immersed. The SLM was constructed by impregnating a porous Fluoropore Teflon (PTFE) membrane with a water-immiscible organic solvent (octanol). In the off-line SPE step, the nonpolar sorbent (C-18, 4,mg) selectively retained the target ochratoxin, enabling small volumes of acceptor phase (1,mL) to be introduced. The captured analytes were eluted in a small volume of methanol (0.1,mL). This procedure resulted in sample cleanup and concentration enhancement. The method was evaluated for accuracy and precision, and its RSD found to be 5%. The LODs for OA in the standard solutions and wine samples were 0.5 and 30,,g/L, respectively. The results obtained demonstrate that SLM combined with off-line is a good alternative to the use of immunoaffinity columns prior to CE analysis. [source] In vivo simultaneous monitoring of ,-aminobutyric acid, glutamate, and L -aspartate using brain microdialysis and capillary electrophoresis with laser-induced fluorescence detection: Analytical developments and in vitro/in vivo validationsELECTROPHORESIS, Issue 18 2003Valérie Sauvinet Abstract ,-Aminobutyric acid (GABA), glutamate (Glu), and L -aspartate (L -Asp) are three major amino acid neurotransmitters in the central nervous system. In this work, a method for the separation of these three neurotransmitters in brain microdialysis samples using a commercially available capillary electrophoresis (CE) system has been developed. Molecules were tagged on their primary amine function with the fluorogene agent naphthalene-2,3-dicarboxaldehyde (NDA), and, after separation by micellar electrokinetic chromatography, were detected by laser-induced fluorescence using a 442 nm helium-cadmium laser. The separation conditions for the analysis of derivatized neurotransmitters in standard solutions and microdialysates have been optimized, and this method has been validated on both pharmacological and analytical basis. The separation of GABA, Glu, and L -Asp takes less than 10 min by using a 75 mmol/L borate buffer, pH 9.2, containing 70 mmol/L SDS and 10 mmol/L hydroxypropyl-,-cyclodextrin and +,25 kV voltage. The detection limits were 3, 15 nmol/L and, 5 nmol/L for GABA, Glu, and L -Asp, respectively. Moreover, submicroliter samples can be analyzed. This method allows a simple, rapid and accurate measurement of the three amino acid neurotransmitters for the in vivo brain monitoring using microdialysis sampling. [source] On-line biosensors for simultaneous determination of glucose, choline, and glutamate integrated with a microseparation systemELECTROPHORESIS, Issue 18 2003Guoyue Shi Abstract An effective microseparation system integrated with ring-disc electrodes and two microfluidic devices was fabricated for in vivo determination using a microdialysis pump. The major interference of ascorbic acid (AA) was excluded by direct oxidation with ascorbate oxidase. Glucose, glutamate, and choline were successfully determined simultaneously through the biosensors modified with a bilayer of osmium-poly(4-vinylpyridine)gel-horseradish peroxidase (Os-gel-HRP)/glucose oxidase (GOD), glutamate oxidase (GlutaOD) or choline oxidase (ChOD). To stabilize the biosensors, 0.2% polyethylenimine (PEI) was mixed with the oxidases. The cathodic currents of glucose, glutamate, and choline biosensors started to increase after the standard solutions were injected into the microseparation system. The on-line biosensors show a wide calibration range (10,7,10,5 mol/L) with a detection limit of 10,8 mol/L at the working potential of ,50 mV. The variations of glucose, glutamate, and choline were determined simultaneously in a free moving rat when we perfused the medial frontal cortex with 100 ,mol/L N -methyl- D -aspartate (NMDA) solution, which is the agonist of the NMDA receptor. [source] Development of Cu and Zn Isotope MC-ICP-MS Measurements: Application to Suspended Particulate Matter and Sediments from the Scheldt EstuaryGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 2 2008Jérôme C.J. Petit isotopes de Cu et Zn; interférences spectrales et non spectrales; fractionnement de masse instrumental; MC-ICP-MS; sédiments The present study evaluates several critical issues related to precision and accuracy of Cu and Zn isotopic measurements with application to estuarine particulate materials. Calibration of reference materials (such as the IRMM 3702 Zn) against the JMC Zn and NIST Cu reference materials were performed in wet and/or dry plasma modes (Aridus I and DSN-100) on a Nu Plasma MC-ICP-MS. Different mass bias correction methods were compared. More than 100 analyses of certified reference materials suggested that the sample-calibrator bracketing correction and the empirical external normalisation methods provide the most reliable corrections, with long term external precisions of 0.06 and 0.07, (2SD), respectively. Investigation of the effect of variable analyte to spike concentration ratios on Zn and Cu isotopic determinations indicated that the accuracy of Cu measurements in dry plasma is very sensitive to the relative Cu and Zn concentrations, with deviations of ,65Cu from ,0.4, (Cu/Zn = 4) to +0.4, (Cu/Zn = 0.2). A quantitative assessment (with instrumental mass bias corrections) of spectral and non-spectral interferences (Ti, Cr, Co, Fe, Ca, Mg, Na) was performed. Titanium and Cr were the most severe interfering constituents, contributing to inaccuracies of ,5.1, and +0.60, on ,68/64Zn, respectively (for 500 ,g l,1 Cu and Zn standard solutions spiked with 1000 ,g l,1 of Ti or Cr). Preliminary isotopic results were obtained on contrasting sediment matrices from the Scheldt estuary. Significant isotopic fractionation of zinc (from 0.21, to 1.13, for ,66Zn) and copper (from ,0.38, to 0.23, for ,65Cu), suggest a control by physical mixing of continental and marine water masses, characterized by distinct Cu and Zn isotopic signatures. These results provide a stepping-stone to further evaluate the use of Cu and Zn isotopes as biogeochemical tracers in estuarine environments. L'étude présentée ici porte sur l'évaluation critique d'un certain nombre de paramètres contrôlant la précision et la justesse des mesures des isotopes de Cu et Zn, dans le cadre d'une application à du matériel particulaire estuarien. Une calibration de matériaux de référence (tels que le Zn IRMM 3702) par rapport aux matériaux de référence JMC Zn et NIST Cu a été effectuée avec des plasmas humides et secs (avec Aridus I et DSN-100) sur un MC-ICP-MS Nu. Différentes méthodes de correction de biais de masse ont été comparées. Plus de 100 analyses de matériaux de référence certifiés ont montré que la correction par l'intercalation d'un calibrateur entre chaque échantillon et la calibration externe empirique fournissaient les corrections les plus fiables, avec des précisions externes sur le long terme de 0.06 et 0.07, (2SD) respectivement. Les effets de la variation des rapports de concentrations entre analyte et spike sur les mesures des rapports isotopiques de Cu et Zn ont montré que la justesse des mesures pour Cu en plasma sec est très tributaire des concentrations relatives de Cu et Zn, avec des déviations de ,65Cu allant de ,0.4, (Cu/Zn = 4) à+0.4, (Cu/Zn = 0.2). Une estimation quantitative des interférences spectrales et non spectrales (Ti, Cr, Co, Fe, Ca, Mg, Na) a été faite. Ti et Cr se sont révélés être les constituants interférents les plus importants pouvant entraîner des erreurs de ,5.1, et +0.60, sur ,68/64Zn respectivement (pour des solutions standards à 500 ,g l,1 de Cu et Zn dopées avec 1000 ,g l,1 de Ti ou Cr). Des données isotopiques préliminaires ont été obtenues sur des matrices sédimentaires très différentes provenant de l'estuaire de Scheldt. Les fractionnements significatifs du zinc (de 0.21,à 1.13, pour ,66Zn) et du cuivre (de ,0.38,à 0.23, pour ,65Cu) suggèrent un contrôle par un processus physique de mélange entre des masses d'eaux continentales et marines ayant des signatures isotopiques de Cu et Zn distinctes. Ces résultats constituent un tremplin vers une utilisation future des isotopes de Cu et Zn comme traceurs biogéochimiques des environnements estuariens. [source] Arbutin determination in medicinal plants and creamsINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 2 2009W. Thongchai Synopsis A simple flow injection (FI) manifold with spectrophotometric detection was fabricated and tested for arbutin determination. It is based on the measurement of a red-coloured product at 514 nm formed by the complexation reaction between arbutin and 4-aminoantipyrine (4-AP) in the presence of hexacyanoferrate (III) in an alkaline medium. On injecting 300 ,L standard solutions at various concentrations of arbutin into the FI system under optimum conditions, a linear calibration graph over the range of 1.0,30.0 ,g mL,1 arbutin was established. It is expressed by the regression equation y = 0.2188 ± 0.0036x + 0.1019 ± 0.0366 (r2 = 0.9990, n = 5). The detection limit (3,) and the limit of quantitation (10,) were 0.04 ,g mL,1 and 0.13 ,g mL,1, respectively. The RSD of intraday and interday precisions were found to be 1.2,1.4% and 1.7,2.7%, respectively. The method was successfully applied in the determination of arbutin in four selected fruits and three commercial whitening cream extracts with the mean recoveries of the added arbutin over the range of 96.2,99.0%. No interference effects from some common excipients used in commercial whitening creams were observed. The method is simple, rapid, selective, accurate, reproducible and relatively inexpensive. Résumé Un collecteur simple pour injection en flux (FI) avec détection spectrométrique a été fabriqué et testé pour le dosage de l'arbutine. Son principe repose sur la mesure à 514 nm du produit rouge formé par la réaction de complexation entre l'arbutine et le 4-aminoantipyrine (4-AP) en présence d'hexacyanoferrate (III) en milieu alcalin. On procède à une injection de 300 ,L des solutions standards à diverses concentrations d'arbutine dans le système FI aux conditions optimales, puis on réalise un graphe de calibration linéaire dans l'intervalle de 1,0 à 30,0 ,g mL,1 d'arbutine. Le graphe correspond à l'équation de régression y = 0.2188 ± 0.0036x + 0.1019 ± 0.0366 (r2 = 0.9990, n = 5). La limite de détection (3,) et la limite de quantification (10,) sont respectivement de 0.04 ,g mL,1 et 0.13 ,g mL,1. La RSD des précisions intra et inter jours sont respectivement de 1.2,1.4% et 1.7,2.7%. La méthode a été appliquée avec succès à la mesure de l'arbutine dans 4 fruits sélectionnés et 3 extraits de crèmes de blanchiment commercialisées avec une recouvrance moyenne de l'arbutine ajoutée de 96.2 à 99%. Aucune interférence avec les excipients communément utilisés dans les crèmes de blanchiment commerciales n'a été observée. La méthode est simple, rapide, sélective, précise, reproductible et relativement bon marché. [source] The use of colloidal gas aphrons as novel downstream processing for the recovery of astaxanthin from cells of Phaffia rhodozymaJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2008Maria Dermiki Abstract BACKGROUND: There is an increasing interest in obtaining natural products with bioactive properties, using fermentation technology. However, the downstream processing consisting of multiple steps can be complicated, leading to increase in the final cost of the product. Therefore there is a need for integrated, cost-effective and scalable separation processes. RESULTS: The present study investigates the use of colloidal gas aphrons (CGA), which are surfactant-stabilized microbubbles, as a novel method for downstream processing. More particularly, their application for the recovery of astaxanthin from the cells of Phaffia rhodozyma is explored. Research carried out with standard solutions of astaxanthin and CGA generated from the cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) showed that up to 90% recovery can be achieved under optimum conditions, i.e., pH 11 with NaOH 0.2 mol L,1. In the case of the cells' suspension from the fermentation broth, three different approaches were investigated: (a) the conventional integrated approach where CGA were applied directly; (b) CGA were applied to the clarified suspension of cells; and finally (c) the in situ approach, where CGA are generated within the clarified suspension of cells. Interestingly, in the case of the whole suspension (approach a) highest recoveries (78%) were achieved under the same conditions found to be optimal for the standard solutions. In addition, up to 97% recovery of total carotenoids could be achieved from the clarified suspension after pretreatment with NaOH. This pretreatment led to maximum cell disruption as well as optimum conditioning for subsequent CGA separation. CONCLUSIONS: These results demonstrate the potential of CGA for the recovery of bioactive components from complex feedstock. Copyright © 2008 Society of Chemical Industry [source] Detection of Explosives in Hair Using Ion Mobility SpectrometryJOURNAL OF FORENSIC SCIENCES, Issue 3 2008Jimmie C. Oxley Ph.D. Abstract:, Conventional explosives 2,4,6-trinitrotoluene (TNT), nitroglycerin (NG), and ethylene glycol dinitrate (EGDN) sorbed to hair can be directly detected by an ion mobility spectrometer (IMS) in E-mode (for explosives). Terrorist explosive, triacetone triperoxide (TATP), difficult to detect by IMS in E-mode, was detected in N-mode (for narcotics). Three modes of sample introduction to IMS vapor desorption unit were used: (i) placement of hair directly into the unit, (ii) swabbing of hair and placement of swabs (i.e., paper GE-IMS sample traps) into the unit, and (iii) acetonitrile extracts of hair positioned on sample traps and placed into the unit. TNT, NG, and EGDN were detected in E-mode by all three sample introduction methods. TATP could only be detected by the acetonitrile extraction method after exposure of the hair to vapor for 16 days because of lower sensitivity. With standard solutions, TATP detection in E-mode required about 10 times as much sample as EGDN (3.9 ,g compared with 0.3 ,g). IMS in N-mode detected TATP from hair by all three modes of sample introduction. [source] Increased vigabatrin entry into the brain by polysorbate 80 and sodium caprateJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 2 2001D. Dimitrijevic The effects of a non-ionic surfactant, polysorbate 80, and the sodium salt of the saturated fatty acid, sodium caprate (C10), as potential brain absorption enhancers for vigabatrin were studied. Vigabatrin is an enzyme-activated irreversible inhibitor of ,-aminobutyric acid (GABA) transaminase that increases brain and cerebrospinal GABA concentrations in animals and man. Before intravenous administration, a range of concentrations of the surfactants were tested using erythrocyte lysis or the red blood cell lysis test to establish the non-toxic concentration range. Vigabatrin was dissolved in 0.1% polysorbate 80 and 0.1% sodium caprate and administered intravenously in doses of 4 mL kg,1 to male Wistar rats (230,250 g; n = 3). Rats were killed 2 h after drug and surfactant administration and the brains were immediately removed and homogenized in 0.4m perchloric acid. Selected ion monitoring electrospray mass spectrometry was used to determine the concentration of vigabatrin and GABA directly from the perchloric acid extract of the rat brain. This method was developed to increase the speed and efficiency of the analysis by removing the need for complex extraction and derivatization procedures while retaining the specificity of the mass spectrometer as a detector. The stability of both vigabatrin and GABA in perchloric acid was established by monitoring their pseudo molecular ions in standard solutions at timed intervals over 24 h. Although the detection level for vigabatrin and GABA was at least 50 pg, only GABA was detected in rat brain. Vigabatrin caused a small increase in whole brain GABA. However, GABA levels were higher in the samples with vigabatrin + enhancer than in the samples where vigabatrin alone was administered. One-way analysis of variance indicated a significant effect of the surfactants on GABA levels (F (5,17) = 11.86, P < 0.01) and vigabatrin absorption was presumed. The rectal temperature of the rats is lowered by the presence of vigabatrin in the brain. Vigabatrin alone decreased rectal temperature by 6%. When given with either polysorbate 80 or sodium caprate, the extent of temperature lowering was significantly greater (P < 0.001). There was no significant difference after 2 h between polysorbate 80 + vigabatrin, and sodium caprate + vigabatrin. [source] Determination of some hydroxybenzoic acids and catechins in white wine samples by liquid chromatography with luminescence detectionJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2006Rafael Carlos Rodríguez-Díaz Abstract A liquid chromatographic method with luminescence detection for the determination of eight phenolic compounds is reported. The method involves postcolumn derivatization with terbium(III). This derivatization is based on the reaction between phenolics and terbium(III) to form luminescent chelates, which were determined at ,ex 295 and ,em 545 nm using the fluorescence mode. The long wavelength emission of lanthanide chelates can minimize interferences from background sample matrix, which usually emit at shorter wavelengths. Also, the chromatographic separation allows the individual determination of phenolics, which cannot be done using the direct measurement of the fluorescence of their corresponding terbium chelates. Dynamic ranges of the calibration graphs and detection limits, obtained with standard solutions of analytes were (,g/mL): gallic acid (0.9,40, 0.3), protocatechuic acid (0.05,7, 0.016), catechin (0.2,40, 0.07), vanillic acid (0.25,40, 0.08), p -hydroxybenzoic acid (0.8,40, 0.25), syringic acid (0.17,40, 0.05), epicatechin (0.3,40, 0.09) and salicylic acid (0.07,12, 0.02). The precision was established at two concentration levels of each analyte and expressed as the percentage of RSD with values ranging between 1.0 and 6.5%. The practical usefulness of the method was demonstrated by the analysis of white wine samples, which were diluted two-fold and directly injected into the chromatographic system. The recovery values obtained ranged between 93.3 and 108.0%. [source] Determination of phenol using an enhanced chemiluminescent assayLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 1 2003A. D. Ilyina Abstract Enhanced chemiluminescence (ECL) describes the phenomenon of increased light output in the luminol oxidation reaction catalysed by horseradish peroxidase (HRP) in the presence of certain compounds, such as para -iodophenol. In this work, the effects of phenol on the para -iodophenol-enhanced HRP-catalysed chemiluninescent reaction intensity in an aqueous buffer (Tris,HCl buffer, pH 8.5) and in a surfactant,water,octane mixture were compared. Preincubation of HRP at low phenol concentrations stimulated the chemiluminescent intensity in the assay performed in an aqueous buffer, but did not have significant effect in the sodium bis(2-ethylhexyl)sulphosuccinate) (Aerosol OT, AOT) applied system. It was also observed that HRP preincubation with phenol concentration higher than 0.003,mg/mL produced an inhibitory effect on the enzyme activity for both assay systems. Only an inhibitory effect of phenol on the chemiluminescent intensity in the surfactant system in octane (as organic solvent) was observed. Three assays were developed to determine phenol concentration in water and in an organic solvent mixture. The detection limits were 0.006, 0.003 and 0.0005,mg/mL, respectively, for the buffer-containing system, the AOT-applied system with phenol standard solutions in water and for the AOT-applied system with phenol standard solutions in octane. Copyright © 2002 John Wiley & Sons, Ltd. [source] Electrospray ionisation with selected reaction monitoring for the determination of Mn-citrate, Fe-citrate, Cu-citrate and Zn-citrateRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2009Volker Nischwitz Citrate complexes of Mn and Fe, and potentially those of Cu and Zn, are considered as important low molecular mass species in human serum and cerebrospinal fluid (CSF). For example, Mn is supposed to enter the brain under excess exposure as Mn-citrate leading to neurotoxic effects. Mn-citrate has been characterised in human CSF using chromatography and electrophoresis online with inductively coupled plasma mass spectrometry, but not yet with molecular mass spectrometry. Therefore, this study explores the potential of electrospray ionisation (ESI) with selected reaction monitoring (SRM) for the detection of metal-citrate complexes, in particular Mn-citrate. The collision-induced dissociation of precursor ions with various metal:citrate stoichiometries was studied for Mn-citrate, Fe-citrate, Cu-citrate and Zn-citrate. High selectivity was achieved for Mn(II)-citrate even in respect to Fe(III)-citrate which forms isobaric precursor ions. The limit of detection for Mn-citrate was estimated to be around 250,µg,L,1 (referring to the total Mn content in the standard) using flow injection. The sensitivity was sufficient for the determination of Mn-citrate in standard solutions and in an extract of an Mn-citrate-containing supplement. An improved ESI source design is expected to reduce the limits of detection significantly. The developed ESI-SRM method has the potential to provide complementary data for the quality control of current separation methods for metal citrates using element-selective detection, with application to biomedical samples and further matrices. Copyright © 2009 John Wiley & Sons, Ltd. [source] Using multivariate statistical methods to model the electrospray ionization response of GXG tripeptides based on multiple physicochemical parametersRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2009M. A. Raji Response factors were determined for twelve GXG peptides (where G stands for glycine and X is any of alanine [A], arginine [R], asparagine [N], aspartic acid [D], glycine [G], histidine [H], leucine [L], lysine [K], phenylalanine [F], serine [S], tyrosine [Y], valine [V]) by electrospray ionization mass spectrometry (ESI-MS). The response factors were measured using a novel flow injection method. This new method is based on the Gaussian distribution of analyte concentration resulting from band-broadening dispersion experienced by the analyte upon passage through an extended volume of PEEK tubing. This method removes the need for preparing a discrete series of standard solutions to assess concentration-dependent response. Relative response factors were calculated for each peptide with reference to GGG. The observed trends in the relative response factors were correlated with several analyte physicochemical parameters, chosen based on current understanding of ion release from charged droplets during the ESI process. These include analyte properties: nonpolar surface area; polar surface area; gas-phase basicity; proton affinity; and Log D. Multivariate statistical analysis using multiple linear regression, decision tree, and support vector regression models were investigated to assess their potential for predicting ESI response based on the analyte properties. The support vector regression model was more versatile and produced the least predictive error following 12-fold cross-validation. The effect of variation in solution pH on the relative response factors is highlighted, as evidenced by the different predictive models obtained for peptide response at two pH values (pH,=,6.0 and 9.0). The relationship between physicochemical parameters and associated ionization efficiencies for GXG tripeptides is discussed based on the equilibrium partitioning model. Copyright © 2009 John Wiley & Sons, Ltd. [source] Improved method for isotopic and quantitative analysis of dissolved inorganic carbon in natural water samplesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2006Nelly Assayag We present here an improved and reliable method for measuring the concentration of dissolved inorganic carbon (DIC) and its isotope composition (,13CDIC) in natural water samples. Our apparatus, a gas chromatograph coupled to an isotope ratio mass spectrometer (GCIRMS), runs in a quasi-automated mode and is able to analyze about 50 water samples per day. The whole procedure (sample preparation, CO2(g),CO2(aq) equilibration time and GCIRMS analysis) requires 2 days. It consists of injecting an aliquot of water into a H3PO4 -loaded and He-flushed 12,mL glass tube. The H3PO4 reacts with the water and converts the DIC into aqueous and gaseous CO2. After a CO2(g),CO2(aq) equilibration time of between 15 and 24,h, a portion of the headspace gas (mainly CO2+He) is introduced into the GCIRMS, to measure the carbon isotope ratio of the released CO2(g), from which the ,13CDIC is determined via a calibration procedure. For standard solutions with DIC concentrations ranging from 1 to 25,mmol,·,L,1 and solution volume of 1,mL (high DIC concentration samples) or 5,mL (low DIC concentration samples), ,13CDIC values are determined with a precision (1,) better than 0.1,. Compared with previously published headspace equilibration methods, the major improvement presented here is the development of a calibration procedure which takes the carbon isotope fractionation associated with the CO2(g),CO2(aq) partition into account: the set of standard solutions and samples has to be prepared and analyzed with the same ,gas/liquid' and ,H3PO4/water' volume ratios. A set of natural water samples (lake, river and hydrothermal springs) was analyzed to demonstrate the utility of this new method. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||