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Matrix Effects (matrix + effects)
Kinds of Matrix Effects Selected AbstractsPolymer Matrix Effects on the Nonlinear Optical Response of Incorporated Chromophore: New Analytical ModelsCHEMPHYSCHEM, Issue 10 2006Marina Yu. Abstract A new approach aimed at the modeling of the nonlinear optical (NLO) response of a dipole chromophore incorporated into a locally anisotropic, deformable, polarizable polymer matrix is suggested. The general continuum methodology is used with a specific cavity ansatz being employed; the cavity is chosen to be conformal to the characteristic ellipsoid of the generalized permittivity tensor of the polymer medium. The suggested ansatz allows the electrostatic boundary value problem to be solved analytically, and the local field experienced by the chromophore in the polymer electret to be found. Four analytically solvable models, which correspond to two singular and two nonsingular models, are considered; in two of them the chromophore is characterized by singular dipole and quadrupole moments; the other two use the approximation of the electric moment of the chromophore with that of the polarized ellipsoid. The relation between the macroscopic polymer properties and the microscopic characteristics of the NLO chromophore is established. The compliance of the obtained formulas for the local field with those of the classical Onsager approach is analyzed, and their specific features are considered. [source] Impact of activated sludge-derived colloidal organic carbon on behavior of estrogenic agonist recombinant yeast bioassayENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2005R. David Holbrook Abstract The impact of size-fractionated colloidal organic carbon (COC) originating from a biological wastewater treatment facility on the sensitivity of the yeast estrogen screen (YES) bioassay containing the human estrogen receptor (hER) gene was evaluated. Dose-response curves of serially diluted 17,-estradiol (E2), both in the presence and absence of COC, were generated by the YES bioassay. The concentration of E2 leading to a 50% YES response (effective concentration 50%, or EC50) was used to evaluate quantitatively the estrogenic activity of the different COC-E2 mixtures. The EC50 values for all COC size fractions, including COC-free samples (<1 kD), were statistically greater than the controls using Milli-Q water. Normalized EC50 values significantly increased as a function of COC concentration for the larger size fractions (>0.22 ,m), but were not significantly affected by smaller COC material at environmental levels (1,5 mg/L), while both colloidal polysaccharide concentrations and colloidal fluorophores (measured at an excitation/emission wavelength pair of 350 nm/450 nm) appear to have an important role in the sensitivity of the YES bioassay. Estimates of the colloid-associated E2 fraction did not predict accurately increases in EC50 values. Matrix effects of the specific environment being tested with the YES bioassay need to be evaluated closely due to the sensitivity of the hER and reporter plasmid. [source] Matrix effects on accurate mass measurements of low-molecular weight compounds using liquid chromatography-electrospray-quadrupole time-of-flight mass spectrometry,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 3 2006F. Calbiani Abstract Liquid chromatography (LC) with high-resolution mass spectrometry (HRMS) represents a powerful technique for the identification and/or confirmation of small molecules, i.e. drugs, metabolites or contaminants, in different matrices. However, reliability of analyte identification by HRMS is being challenged by the uncertainty that affects the exact mass measurement. This parameter, characterized by accuracy and precision, is influenced by sample matrix and interferent compounds so that questions about how to develop and validate reliable LC-HRMS-based methods are being raised. Experimental approaches for studying the effects of various key factors influencing mass accuracy on low-molecular weight compounds (MW < 150 Da) when using a quadrupole-time-of-flight (QTOF) mass analyzer were described. Biogenic amines in human plasma were considered for the purpose and the effects of peak shape, ion abundance, resolution and data processing on accurate mass measurements of the analytes were evaluated. In addition, the influence of the matrix on the uncertainty associated with their identification and quantitation is discussed. A critical evaluation on the calculation of the limits of detection was carried out, considering the uncertainty associated with exact mass measurement of HRMS-based methods. The minimum concentration level of the analytes that was able to provide a statistical error lower than 5 ppm in terms of precision was 10 times higher than those calculated with S/N = 3, thus suggesting the importance of considering both components of exact mass measurement uncertainty in the evaluation of the limit of detection. Copyright © 2006 John Wiley & Sons, Ltd. [source] Matrix effects in quantitative pesticide analysis using liquid chromatography,mass spectrometryMASS SPECTROMETRY REVIEWS, Issue 6 2006W.M.A. Niessen Abstract Combined liquid chromatography,mass spectrometry using electrospray or atmospheric-pressure chemical ionization has become an important tool in the quantitative analysis of pesticide residues in various matrices in relation to environmental analysis, food safety, and biological exposure monitoring. One of the major problems in the quantitative analysis using LC,MS is that compound and matrix-dependent response suppression or enhancement may occur, the so-called matrix effect. This article reviews issues related to matrix effects, focusing on quantitative pesticide analysis, but also paying attention to expertise with respect to matrix effects acquired in other application areas of LC,MS, especially quantitative bioanalysis in the course of drug development. © 2006 Wiley Periodicals, Inc. [source] Evaluation of ELISA for imidacloprid detection in eastern hemlock (Tsuga canadensis) wood and needle tissuesPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 2 2009Brian M Eisenback Abstract BACKGROUND: Imidacloprid is the primary insecticide used against the exotic invasive insect hemlock woolly adelgid, Adelges tsugae Annand, a pest of eastern hemlock [Tsuga canadensis (L.) Carrière] trees in the eastern United States. A competitive enzyme-linked immunosorbent assay (ELISA) was evaluated for quantification of imidacloprid in eastern hemlock wood and needle tissues. RESULTS: Matrix effects in the form of false positives and overestimated imidacloprid concentrations were observed in both wood and needle extracts. Tissues required a 100,1000-fold dilution with water in order to reduce matrix effects. Standard curves in 1% wood or needle extract were not significantly different from standard curves prepared in water. Matrix effects were more pronounced at concentrations in the lower working range of the kit, with recovery of 5 µg L,1 imidacloprid more accurate than recovery of 0.2 µg L,1. CONCLUSION: ELISA remains a valuable tool for semi-quantitative imidacloprid detection within the hemlock system because of its sensitivity, cost and ease of use. However, a 1000-fold dilution of hemlock tissue extract is recommended to ensure accurate imidacloprid determinations. Copyright © 2008 Society of Chemical Industry [source] Determination of nickel, calcium and magnesium in xylem sap by flame atomic absorption spectrometry using a microsampling techniquePHYTOCHEMICAL ANALYSIS, Issue 5 2009Sheila Alves Abstract Introduction Knowledge of xylem sap chemical composition is important to the understanding of translocation, detoxification and tolerance mechanisms. However, the small amount of sample available often hampers its characterisation. Hence, low volume consumption techniques are needed for xylem sap analysis. Objective To develop a microsampling technique for the determination of elements in xylem sap from different plants by flame atomic absorption spectrometry (FAAS). Methodology The microsampling device was optimised in terms of sample volume and integration time. The analytical characteristics of the microsampling technique (µ -FAAS) were established and compared with those of FAAS with traditional continuous nebulisation. The method was validated by means of an independent technique. Results Ca, Mg and Ni were determined in a 50 µL aliquot of xylem sap solution/element that was introduced directly into the flame via the microsampling accessory. Good precision was obtained with relative standard deviations of 1.1, 0.6 and 2.3% for Ca, Mg and Ni, respectively. Matrix effects resulting from the physical characteristics of the samples and possible chemical interferences caused by phosphate and/or sulphate were ruled out. Conclusion A simple, rapid and reproducible microsampling technique coupled to FAAS was developed and successfully applied in the determination of Ca, Mg and Ni in xylem sap. Copyright © 2009 John Wiley & Sons, Ltd. [source] Matrix effects during analysis of plasma samples by electrospray and atmospheric pressure chemical ionization mass spectrometry: practical approaches to their eliminationRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2003Joachim Schuhmacher Some cases of occurrence of matrix effects (mostly ion suppression) in protein-precipitated plasma samples, and their influence on the validity of plasma concentrations and pharmacokinetic parameters, are discussed. The comparison of matrix effects using either electrospray (TurboIonspray, TISP) or atmospheric pressure chemical ionization (APCI) indicated that APCI is less prone to matrix effects. Nevertheless, TISP is usually the first choice of ionization technique since unknown thermally labile metabolites might be present in the plasma samples causing erroneous results. A high impact of ion suppression on the plasma concentrations after intravenous (i.v.) administration was found, depending on the drug formulation (vehicle). Since ion suppression caused significantly lower plasma concentrations (by a factor of up to 5.5) after i.v. dosing, the area under the curve (AUC) was underestimated and the plasma clearance was consequently erroneously high, with an impact on drug candidate selection. By simple stepwise dilution (e.g. 10-fold and 50-fold) of the supernatant of protein-precipitated plasma samples, including all calibration and quality control samples, the matrix effects were recognized and eliminated. Copyright © 2003 John Wiley & Sons, Ltd. [source] Arsenic and thallium data in environmental samples: Fact or fiction?REMEDIATION, Issue 4 2010Susan D. Chapnick Matrix effects may increasingly lead to erroneous environmental decisions as regulatory limits or risk-based concentrations of concern for trace metals move lower toward the limits of analytical detection. A U.S. Environmental Protection Agency Office of Technical Standards Alert estimated that environmental data reported using inductively coupled plasma spectrometry (ICP-AES) has a false-positive rate for thallium of 99.9 percent and for arsenic of 25 to 50 percent. Although this does not seem to be widely known in the environmental community, using three case studies, this article presents data in environmental samples that demonstrate severe matrix effects on the accuracy of arsenic and thallium results. Case Study 1 involves soil results with concentrations that approached or exceeded the applicable regulatory soil cleanup objectives of 13 mg/kg for arsenic and 2 mg/kg for thallium. Reanalysis using ICP coupled with a mass spectrometer (ICP-MS) confirmed all thallium results were false positives and all arsenic results were biased high, concluding no action was required for soil remediation. Case Study 2 involves groundwater results for thallium at a Superfund site, where thallium was detected in groundwater up to 21.6 , g/L using ICP-AES. Reanalysis by ICP-MS reported thallium as nondetect below the applicable regulatory level in all samples. ICP-MS is usually a more definitive and accurate method of analysis compared to ICP-AES; however, this is not always the case, as we demonstrate in Case Study 3, using data from groundwater samples at an industrial site. Through a weight-of-evidence approach, it is demonstrated that although method quality control results were acceptable, interferences in some groundwater samples caused biased high results for arsenic using ICP-MS, which were significantly lower when reanalyzed using hydride generation atomic fluorescence spectrometry. Causes of these interference effects and conclusions from the three case studies to obtain accurate metal data for site assessment, risk characterization, and remedy selection are discussed. © 2010 Wiley Periodicals, Inc. [source] Simultaneous assay of sildenafil and desmethylsildenafil in neonatal plasma by ultra-performance liquid chromatography,tandem mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 2 2010Bregje C. Witjes Abstract Sildenafil is used to treat pulmonary hypertension in neonatal and pediatric patients. Pharmacokinetic studies in these patients are complicated by the limited sample volume. We present the validation results of an assay method to quantitate sildenafil and desmethylsildenafil simultaneously in 50,µL of plasma. Deuterated sildenafil was used as an internal standard. After liquid,liquid extraction, analytes were separated on an ultra-performance liquid chromatography (UPLC)-column and quantified via tandem mass spectrometry. The calibration range was linear, with acceptable accuracy and a precision of <15% for both compounds. The lower limits of quantification were 1,ng/mL. Matrix effects were present, but inter-plasma batch variability was under 12%. The method was successfully applied to samples from a pharmacokinetic study into sildenafil pharmacokinetics in neonates, making maximum use of the limited number and amount of plasma samples available. Copyright © 2009 John Wiley & Sons, Ltd. [source] Development of liquid chromatography/mass spectrometry methods for the quantitative analysis of herbal medicine in biological fluids: a reviewBIOMEDICAL CHROMATOGRAPHY, Issue 1 2010Michael J. Gray Abstract The development of liquid chromatography,mass spectrometry (LC-MS) and tandem MS/MS for the analysis of bioactive components and their metabolites of herbal medicines in biological fluids is reviewed with the aim of providing an overview of the current techniques and methods used. The issues and challenges associated with various stages of the analytical method development are discussed using Ginkgo biloba and Panax ginseng as case studies. LC-MS offers selectivity and specificity in both the chromatographic separation and detection steps. This is necessary in order to measure compounds at extremely low concentrations as is often observed in plasma and urine samples. Traditional methods of detection (UV,visible) do not offer sufficient selectivity and specificity needed. The strategies and pitfalls involved with the measurement of such compounds are discussed in this review. Matrix effects, ,unseen' matrix suppression and enhancement ionization effects can significantly reduce the accuracy and precision of the measurement. The impact of the correct choice of chromatography column formats on signal-to-noise ratio is also discussed. Analytical methods from sample preparation to mass spectrometric detection is outlined in order to provide good direction for analysts intent on the measurement of bioavailable compounds from herbal medicines in plasma and urine samples. Copyright © 2009 John Wiley & Sons, Ltd. [source] Assessment of matrix effects and determination of niacin in human plasma using liquid,liquid extraction and liquid chromatography,tandem mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 11 2008Michael C. Peoples Abstract A simple, sensitive and rapid liquid,liquid extraction method for the analysis of nicotinic acid (niacin) and its labeled internal standard nicotinic acid-d4 (niacin-d4) in human plasma was developed and validated. The analyte and its internal standard were isolated from acidified plasma using a single liquid,liquid extraction procedure with methyl- t -butyl ether. The extracted samples were analyzed by liquid chromatography,tandem mass spectrometry in positive electrospray ionization mode with multiple reaction monitoring. The calibration curves were linear in the measured range between 5 and 1000 ng/mL and the limit of detection was calculated as 122 pg/mL. The method required 250 µL of human plasma and the total run time between injections was 3.5 min. Matrix effects were assessed by post-column infusion experiments, phospholipids monitoring and post-extraction addition experiments. The extraction of phospholipids and niacin from plasma was studied under acidic, neutral and basic conditions. Acidic conditions were optimal for both the recovery of niacin and the removal of phospholipids; the degree of matrix effects for niacin was determined to be 2.5%. It was concluded that effective removal of matrix components can overcome low recovery issues associated with liquid,liquid extractions of polar analytes. Copyright © 2008 John Wiley & Sons, Ltd. [source] Direct injection horse-urine analysis for the quantification and confirmation of threshold substances for doping control.DRUG TESTING AND ANALYSIS, Issue 8 2009Abstract Levodopa and dopamine have been abused as performance-altering substances in horse racing. Urinary 3-methoxytyramine is used as an indicator of dopaminergic manipulation resulting from dopamine or levodopa administration and is prohibited with a urinary threshold of 4 µg mL,1 (free and conjugated). A simple liquid chromatographic (LC)/mass spectrometric (MS) (LCMS) method was developed and validated for the quantification and identification of 3-methoxytyramine in equine urine. Sample preparation involved enzymatic hydrolysis and protein precipitation. Hydrophilic interaction liquid chromatography (HILIC) was selected as a separation technique that allows effective retention of polar substances like 3-methoxytyramine and efficient separation from matrix compounds. Electrospray ionization (ESI) in positive mode with product ion scan mode was chosen for the detection of the analytes. Quantification of 3-methoxytyramine was performed with fragmentation at low collision energy, resulting in one product ion, while a second run at high collision energy was performed for confirmation (at least three abundant ions). Studies on matrix effects showed ion suppression depending on the horse urine used. To overcome the variability of the results originating from the matrix effects, isotopic labelled internal standard was used and linear regression calibration methodology was applied for the quantitative determination of the analyte. The tested linear range was 1,20 µg mL,1. The relative standard deviations of intra- and inter- assay analysis of 3-methoxytyramine in horse urine were lower than 4.2% and 3.2%, respectively. Overall accuracy (relative percentage error) was less than 6.2%. The method was applied to case samples, demonstrating simplicity, accuracy and selectivity. Copyright © 2009 John Wiley & Sons, Ltd. [source] Evaluation of Cu,Ethylenediamine Metal Ion Buffers as Calibrants for Ion-Selective Electrode Measurement of Copper in Fresh Water SystemsELECTROANALYSIS, Issue 10 2005Ling Zeng Abstract An investigation was made into the accuracy of cupric ion selective electrode (ISE) measurement of Cu in solutions approximating acidic freshwaters with Cu-ethylenediamine buffers used as the calibrants. This method overestimates the free Cu compared with calibration using Cu(NO3)2 standards, the standard addition method, and speciation modelling calculations. Statistical tests showed a small, but significant, difference between the intercepts of the linear Nernstian regressions of the calibration plots of Cu-en buffer standardisation and direct calibration with Cu(NO3)2 standards in matrix that matches the samples. The difference in the intercepts, which corresponds with Eo values of the electrode, is not well understood, but is possibly caused by potentially interfering cations such as Fe2+. The results of this study showed that down to 10,8,M Cu2+, where a linear Nernstian response is possible, the Cu ISE is probably better calibrated using Cu standards prepared in the same matrix as the sample solutions to avoid potential matrix effects. [source] Capillary electrophoresis-time of flight-mass spectrometry using noncovalently bilayer-coated capillaries for the analysis of amino acids in human urineELECTROPHORESIS, Issue 12 2008Rawi Ramautar Abstract A capillary electrophoresis-time of flight-mass spectrometry (CE-TOF-MS) method for the analysis of amino acids in human urine was developed. Capillaries noncovalently coated with a bilayer of Polybrene (PB) and poly(vinyl sulfonate) (PVS) provided a considerable EOF at low pH, thus facilitating the fast separation of amino acids using a BGE of 1,M formic acid (pH,1.8). The PB,PVS coating proved to be very consistent yielding stable CE-MS patterns of amino acids in urine with favorable migration time repeatability (RSDs <2%). The relatively low sample loading capacity of CE was circumvented by an in-capillary preconcentration step based on pH-mediated stacking allowing 100-nL sample injection (i.e. ca. 4% of capillary volume). As a result, LODs for amino acids were down to 20,nM while achieving satisfactory separation efficiencies. Preliminary validation of the method with urine samples showed good linear responses for the amino acids (R2 >0.99), and RSDs for peak areas were <10%. Special attention was paid to the influence of matrix effects on the quantification of amino acids. The magnitude of ion suppression by the matrix was similar for different urine samples. The CE-TOF-MS method was used for the analysis of urine samples of patients with urinary tract infection (UTI). Concentrations of a subset of amino acids were determined and compared with concentrations in urine of healthy controls. Furthermore, partial least squares,discriminant analysis (PLS,DA) of the CE-TOF-MS dataset in the 50,450,m/z region showed a distinctive grouping of the UTI samples and the control samples. Examination of score and loadings plot revealed a number of compounds, including phenylalanine, to be responsible for grouping of the samples. Thus, the CE-TOF-MS method shows good potential for the screening of body fluids based on the analysis of endogenous low-molecular weight metabolites such as amino acids and related compounds. [source] On-line automatic SPE-CE coupling for the determination of biological markers in urineELECTROPHORESIS, Issue 5 2007José Ruiz-Jiménez Abstract Automatic SPE has been coupled on-line to CE by a transfer tube and the replenishment system of the CE instrument. The approach allows the target analytes (viz. creatinine, creatine, xanthine, hypoxanthine, uric acid, p -aminohippuric acid and ascorbic acid in urine samples) to be removed from the sample matrix, cleaned up, preconcentrated and injected into the capillary. The detection limits range between 0.14 and 4.50,,g/mL, the quantification limits between 0.45 and 15.0,,g/mL, and linear dynamic ranges , which include the reference healthy human values , from the quantification limits to 1332,,g/mL. The precision, expressed as RSD, ranges between 0.38 and 2.22% for repeatability and between 1.79 and 7.61% for within-laboratory reproducibility. The errors, expressed as RSD for all compounds, range between 0.20 and 6.90%. The time for automatic SPE and that necessary for the individual separation,detection of the target analytes are 13 and 12,min, respectively; the analysis frequency is 5,h,1. The accuracy of the method and potential matrix effects were studied by using spiked samples and recoveries between 96.00 and 103.07 % were obtained. The proposed method was applied to samples from healthy young students. [source] Benzo[a]pyrene bioavailability from pristine soil and contaminated sediment assessed using two in vitro modelsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2007Luba Vasiluk Abstract A major route of exposure to hydrophobic organic contaminants (HOCs), such as benzo[a]pyrene (BaP), is ingestion. Matrix-bound HOCs may become bioavailable after mobilization by the gastrointestinal fluids followed by sorption to the intestinal epithelium. The purpose of this research was to measure the bioavailability of [14C]-BaP bound to pristine soils or field-contaminated sediment using an in vitro model of gastrointestinal digestion followed by sorption to human enterocytes (Caco-2 cells) or to a surrogate membrane, ethylene vinyl acetate (EVA) thin film. Although Caco-2 cells had a twofold higher lipid-normalized fugacity capacity than EVA, [14C]-BaP uptake by Caco-2 lipids and EVA thin film demonstrated a linear relationship within the range of BaP concentrations tested. These results suggest that EVA thin film is a good membrane surrogate for passive uptake of BaP. The in vitro system provided enough sensitivity to detect matrix effects on bioavailability; after 5 h, significantly lower concentrations of [14C]-BaP were sorbed into Caco-2 cells from soil containing a higher percentage of organic matter compared to soil with a lower percentage of organic matter. The [14C]-BaP desorption rate from Caco-2 lipids consistently was twofold higher than from EVA thin film for all matrices tested. The more rapid kinetics observed with Caco-2 cells probably were due to the greater surface area available for absorption/desorption in the cells. After 5 h, the uptake of BaP into Caco-2 lipid was similar in live and metabolically inert Caco-2 cells, suggesting that the primary route of BaP uptake is by passive diffusion. Moreover, the driving force for uptake is the fugacity gradient that exists between the gastrointestinal fluid and the membrane. [source] Determination of Lithium Contents in Silicates by Isotope Dilution ICP-MS and its Evaluation by Isotope Dilution Thermal Ionisation Mass SpectrometryGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 3 2004Takuya Moriguti Lithium; ICP-MS avec dilution isotopique; TIMS; matériaux silicatés de référence; météorites A precise and simple method for the determination of lithium concentrations in small amounts of silicate sample was developed by applying isotope dilution-inductively coupled plasma-mass spectrometry (ID-ICP-MS). Samples plus a Li spike were digested with HF-HClO4, dried and diluted with HNO3, and measured by ICP-MS. No matrix effects were observed for 7Li/6Li in rock solutions with a dilution factor (DF) of 97 at an ICP power of 1.7 kW. By this method, the determination of 0.5 ,g g -1 Li in a silicate sample of 1 mg can be made with a blank correction of < 1%. Lithium contents of ultrabasic to acidic silicate reference materials (JP-1, JB-2, JB-3, JA-1, JA-2, JA-3, JR-1 and JR-2 from the Geological Survey of Japan, and PCC-1 from the US Geological Survey) and chondrites (three different Allende and one Murchison sample) of 8 to 81 mg were determined. The relative standard deviation (RSD) was typically < 1.7%. Lithium contents of these samples were further determined by isotope dilution-thermal ionisation mass spectrometry (ID-TIMS). The relative differences between ID-ICP-MS and ID-TIMS were typically < 2%, indicating the high accuracy of ID-ICP-MS developed in this study. Nous avons développé une méthode simple et précise de détermination des concentrations en lithium dans de très petits échantillons silicatés. Elle est basée sur la méthode de dilution isotopique couplée à l'analyse par spectrométrie de masse avec couplage induit (ID-ICP-MS). Les échantillons auxquels est ajouté le spike de Li, sont mis en solution avec un mélange HF-HclO4, évaporés à sec, puis repris avec HNO3 et analysés à l'ICP-MS. Aucun effet de matrice n'est observé sur les rapports 7Li/6Li dans les solutions quand les facteurs de dilution sont 97 et qu'elles sont analysées avec une puissance du plasma de 1.7 kW. Par cette méthode, la détermination de 0.5 ,g g -1 de Li dans un échantillon silicaté de 1 mg peut être effectuée avec une correction de blanc < 1 %. Les teneurs en lithium des matériaux de référence de composition ultrabasique à acide (JP-1, JB-2, JB-3, JA-1, JA-2, JA-3, JR- 1 et JR-2 du Service Géologique du Japon, et PCC-1 du Service Géologique des USA) et de chondrites (trois échantillons différents d'Allende et un de Murchison), de poids variant entre 8 et 81 mg ont été déterminées. La déviation standard relative typique était < 1.7%. Les teneurs en lithium de ces échantillons ont été ensuite mesurées par dilution isotopique et spectrométrie de masse à thermo-ionisation (ID-TIMS). Les différences entre les résultats obtenus par ID-ICP-MS et ID-TIMS étaient < 2%, démontrant ainsi la grande justesse de la technique ID-ICP-MS développée dans cette étude. [source] FULLPAT: a full-pattern quantitative analysis program for X-ray powder diffraction using measured and calculated patternsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2002Steve J. Chipera FULLPAT is a quantitative X-ray diffraction methodology that merges the advantages of existing full-pattern fitting methods with the traditional reference intensity ratio (RIR) method. Like the Rietveld quantitative analysis method, it uses complete diffraction patterns, including the background. However, FULLPAT can explicitly analyze all phases in a sample, including partially ordered or amorphous phases such as glasses, clay minerals, or polymers. Addition of an internal standard to both library standards and unknown samples eliminates instrumental and matrix effects and allows unconstrained analyses to be conducted by direct fitting of library standard patterns to each phase in the sample. Standard patterns may include data for any solid material including glasses, and calculated patterns may also be used. A combination of standard patterns is fitted to observed patterns using least-squares minimization, thereby reducing user intervention and bias. FULLPAT has been coded into Microsoft EXCEL using standard spreadsheet functions. [source] Optimization of the ESI and APCI experimental variables for the LC/MS determination of s-triazines, methylcarbamates, organophosphorous, benzimidazoles, carboxamide and phenylurea compounds in orange samplesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2007Guilherme M. Titato Abstract In this work, ten selected pesticides of different chemical groups, indicated to orange culture, were extracted and determined by liquid chromatography,mass spectrometry using both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) operating in the positive ion detection mode. Applying a variables selection technique verified that cone voltage, source temperature and drying-gas flow-rate are the critical variables when the ESI was used, while cone voltage was found to be the only critical variable for the MS system, operating with the APCI ionization mode. After optimization of the most important parameters through the variables selection technique, the selected ion-recording (SIR) mode, monitoring the [M + H]+ species for all the compounds, was applied for the method validation of the pesticides, in both ionization modes. In orange samples, matrix effects did not interfere with the determination of the pesticides. Pesticides quantification limits ranged from 10 to 50 µg kg,1 for ESI and from 8.2 to 45 µg kg,1 for APCI. Linearity was studied from LOQ upto 200 times LOQ values (r > 0.98). Recoveries obtained were in the range of 70.2,100.5% (RSDs less than 10%). In order to guarantee that the identification and confirmation of the studied pesticides in real samples were unequivocal, characteristic fragment ions of the pesticides were obtained by varying the cone voltage (in-source CID). Copyright © 2007 John Wiley & Sons, Ltd. [source] Supported liquid membranes in hollow fiber liquid-phase microextraction (LPME) , Practical considerations in the three-phase modeJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2007Kari Folde Bårdstu Abstract In this work, three-phase liquid-phase microextraction (LPME) based on a supported liquid membrane (SLM) sustained in the wall of a hollow fiber was investigated with special focus on optimization of the experimental procedures in terms of recovery and repeatability. Recovery data for doxepin, amitriptyline, clomipramine, and mianserin were in the range of 67.8,79.8%. Within-day repeatability data for the four basic drugs were in the range of 4.1,7.7%. No single factor was found to be responsible for these variations, and the variability was caused by several factors related to the LPME extractions as well as to the final HPLC determination. Although the volume of the SLM varied within 0.4,3.1% RSD depending on the preparation procedure, and the volume of the acceptor solution varied within 4.8% RSD, both recoveries and repeatability were found to be relative insensitive to these variations. Thus, the handling of microliters of liquid in LPME was not a very critical factor, and the preparation of the SLM was accomplished in several different ways with comparable performance. Reuse of hollow fibers was found to suffer from matrix effects due to built-up of analytes in the SLM, whereas washing of the hollow fibers in acetone was beneficial in terms of recovery, especially for the extraction of the most hydrophobic substances. Several of the organic solvents used in the literature as SLM suffered from poor long-term stability, but silicone oil AR 20 (polyphenyl-methylsiloxane), 2-nitrophenyl octyl ether (NPOE), and dodecyl acetate (DDA) all extracted with unaltered performance even after 60 days of storage at room temperature. [source] Methyl benzoate as a marker for the detection of mold in indoor building materialsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2005Loay Wady Abstract A convenient analytical method to quantify volatile organic compounds (VOCs) emitted from various building materials has not been addressed yet. This work presents a new and rapid automated method using SPME combined with GC/MS. Methyl benzoate , as a metabolic biomarker for mold growth,was used to indicate VOCs and to determine and assess mold growth on damp samples. Gypsum board and wallboard paper were used as examples of common indoor building materials. Optimized extraction conditions were carried out manually, using a GC/flame ionization detector. Moldy samples were analyzed using an automated SPME-GC/MS analysis under optimized conditions. The amount of methyl benzoate emitted from the studied samples ranged from 32 to 46 ppb, where the density of the fungal biomass was found to be 8×104 cells/mL. A relationship between the amount of fungal biomass and the emitted concentration of methyl benzoate was found and assessed based upon cultured mold samples taken from indoor building sites. The analytical method shows promise for the compound methyl benzoate, which can easily be identified at low detection limits (LOD = 3 ppb) and good linearity (> 0.988), and its extraction and detection can be accomplished cleanly by current extraction techniques. Results suggest that this method with easy sample preparation can be used for quantitation and, of importance, minimal matrix effects are observed. [source] Matrix effects in quantitative pesticide analysis using liquid chromatography,mass spectrometryMASS SPECTROMETRY REVIEWS, Issue 6 2006W.M.A. Niessen Abstract Combined liquid chromatography,mass spectrometry using electrospray or atmospheric-pressure chemical ionization has become an important tool in the quantitative analysis of pesticide residues in various matrices in relation to environmental analysis, food safety, and biological exposure monitoring. One of the major problems in the quantitative analysis using LC,MS is that compound and matrix-dependent response suppression or enhancement may occur, the so-called matrix effect. This article reviews issues related to matrix effects, focusing on quantitative pesticide analysis, but also paying attention to expertise with respect to matrix effects acquired in other application areas of LC,MS, especially quantitative bioanalysis in the course of drug development. © 2006 Wiley Periodicals, Inc. [source] Recent advances in mycotoxin determination in food and feed by hyphenated chromatographic techniques/mass spectrometryMASS SPECTROMETRY REVIEWS, Issue 1 2006Stefano Sforza Abstract Mycotoxins are fungal toxins produced by molds, which occur universally in food and feed derivatives, and are produced under certain environmental conditions in the field before harvest, post-harvest, during storage, processing, and feeding. Mycotoxin contamination is one of the most relevant and worrisome problem concerning food and feed safety because it can cause a variety of toxic acute and chronic effects in human and animals. In this review we report the use of mass spectrometry in connection with chromatographic techniques for mycotoxin determination by considering separately the most diffuse class of mycotoxins: patulin, aflatoxins, ochratoxin A, zearalenone, trichothecenes, and fumonisins. Although the selectivity of mass spectrometry is unchallenged if compared to common GC and LC detection methods, accuracy, precision, and sensitivity may be extremely variable concerning the different mycotoxins, matrices, and instruments. The sensitivity issue may be a real problem in the case of LC/MS, where the response can be very different for the different ionization techniques (ESI, APCI, APPI). Therefore, when other detection methods (such as fluorescence or UV absorbance) can be used for the quantitative determination, LC/MS appears to be only an outstanding confirmatory technique. In contrast, when the toxins are not volatile and do not bear suitable chromophores or fluorophores, LC/MS appears to be the unique method to perform quantitative and qualitative analyses without requiring any derivatization procedure. The problem of exact quantitative determination in GC/MS and LC/MS methods is particularly important for mycotoxin determination in food, given the high variability of the matrices, and can be solved only by the use of isotopically labeled internal standards or by the use of ionization interfaces able to lower matrix effects and ion suppressions. When the problems linked to inconstant ionization and matrix effects will be solved, only MS detectors will allow to simplify more and more the sample preparation procedures and to avoid clean-up procedures, making feasible low-cost, high-throughput determination of mycotoxins in many different food matrices. © 2005 Wiley Periodicals, Inc. [source] Evaluation of ELISA for imidacloprid detection in eastern hemlock (Tsuga canadensis) wood and needle tissuesPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 2 2009Brian M Eisenback Abstract BACKGROUND: Imidacloprid is the primary insecticide used against the exotic invasive insect hemlock woolly adelgid, Adelges tsugae Annand, a pest of eastern hemlock [Tsuga canadensis (L.) Carrière] trees in the eastern United States. A competitive enzyme-linked immunosorbent assay (ELISA) was evaluated for quantification of imidacloprid in eastern hemlock wood and needle tissues. RESULTS: Matrix effects in the form of false positives and overestimated imidacloprid concentrations were observed in both wood and needle extracts. Tissues required a 100,1000-fold dilution with water in order to reduce matrix effects. Standard curves in 1% wood or needle extract were not significantly different from standard curves prepared in water. Matrix effects were more pronounced at concentrations in the lower working range of the kit, with recovery of 5 µg L,1 imidacloprid more accurate than recovery of 0.2 µg L,1. CONCLUSION: ELISA remains a valuable tool for semi-quantitative imidacloprid detection within the hemlock system because of its sensitivity, cost and ease of use. However, a 1000-fold dilution of hemlock tissue extract is recommended to ensure accurate imidacloprid determinations. Copyright © 2008 Society of Chemical Industry [source] Photodynamic Characterization and In Vitro Application of Methylene Blue-containing Nanoparticle Platforms,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Wei Tang ABSTRACT This article presents the development and characterization of nanoparticles loaded with methylene blue (MB), which are designed to be administered to tumor cells externally and deliver singlet oxygen (1O2) for photodynamic therapy (PDT), i.e. cell kill via oxidative stress to the membrane. We demonstrated the encapsulation of MB, a photosensitizer (PS), in three types of sub-200 nm nanoparticles, composed of polyacrylamide, sol-gel silica and organically modified silicate (ORMOSIL), respectively. Induced by light irradiation, the entrapped MB generated 1O2), and the produced 1O2 was measured quantitatively with anthracene-9, 10-dipropionic acid, disodium salt, to compare the effects of different matrices on 1O2 delivery. Among these three different kinds of nanoparticles, the polyacrylamide nanoparticles showed the most efficient delivery of 1O2 but its loading of MB was low. In contrast, the sol-gel nanoparticles had the best MB loading but the least efficient 1O2 delivery. In addition to investigating the matrix effects, a preliminary in vitro PDT study using the MB-loaded polyacrylamide nanoparticles was conducted on rat C6 glioma tumor cells with positive photodynamic results. The encapsulation of MB in nanoparticles should diminish the interaction of this PS with the biological milieu, thus facilitating its systemic administration. Furthermore, the concept of the drug-delivering nanoparticles has been extended to a new type of dynamic nanoplatform (DNP) that only delivers 1O2. This DNP could also be used as a targeted multifunctional platform for combined diagnostics and therapy of cancer. [source] Small molecule detection by reflective interferometric Fourier transform spectroscopy (RIFTS)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009Claudia Pacholski Abstract A new method for the compensation of matrix effects in biosensing experiments referred to as reflective interferometric Fourier transform spectroscopy (RIFTS) has been developed recently [1]. It employs a porous silicon sensor comprised of two porous silicon layers stacked one on top of the other. The structure has a complicated reflectivity spectrum that can be resolved by FFT analysis leading to three distinctive peaks which are assigned to the layers in the porous silicon structur. If the double layer is appropriately designed, the bottom layer can act as a reference channel. In this paper the specific sensing of small molecules using RIFTS is demonstrated for the first time. Ac-L-Lys-D-Ala-D-Ala has been immobilized to the sensor surface representing the capture probe and vancomycin was used as target analyte. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Direct quantification of 11-nor-,9 -tetrahydrocannabinol-9-carboxylic acid in urine by liquid chromatography/tandem mass spectrometry in relation to doping control analysisRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2010C. Chebbah An accurate and precise method for the quantification of 11-nor-,9 -tetrahydrocannabinol-9-carboxylic acid (THCA) in urine by liquid chromatography/tandem mass spectrometry (LC/MS/MS) for doping analysis purposes has been developed. The method involves the use of only 200,µL of urine and the use of D9 -THCA as internal standard. No extraction procedure is used. The urine samples are hydrolysed using sodium hydroxide and diluted with a mixture of methanol/glacial acetic acid (1:1). Chromatographic separation is achieved using a C8 column with gradient elution. All MS and MS/MS parameters were optimised in both positive and negative electrospray ionisation modes. For the identification and the quantification of THCA three product ions are monitored in both ionisation modes. The method is linear over the studied range (5,40,ng/mL), with satisfactory intra-and inter-assay precision, and the relative standard deviations (RSDs) are lower than 15%. Good accuracy is achieved with bias less than 10% at all levels tested. No significant matrix effects are observed. The selectivity and specificity are satisfactory, and no interferences are detected. The LC/MS/MS method was applied for the analysis of 48 real urine samples previously analysed with a routine gas chromatography/mass spectrometry (GC/MS) method. A good correlation between the two methods was obtained (r2,>,0.98) with a slope close to 1. Copyright © 2010 John Wiley & Sons, Ltd. [source] Application of hyphenated mass spectrometry techniques for the analysis of urinary free glucocorticoidsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2009Angela Cuzzola Alteration of levels of glucocorticoids in plasma and urine can be related to several diseases. In particular, the determination of endogenous glucocorticoids in urine has been reported to provide information on cortisol and cortisone status, on the activities of steroid hormone enzymes and on glucocorticoid metabolism. In this study, the application of hyphenated mass spectrometry techniques (GC/MS without derivatization and LC/MS) for the simultaneous analysis of free urinary cortisol (F), cortisone (E), tetrahydrocortisol (THF), allo-tetrahydrocortisol (A-THF) and tetrahydrocortisone (THE) was evaluated. A sample preparation protocol by solid-phase extraction, mass spectrometry parameters and chromatographic conditions for both techniques were carefully optimized in terms of extracting phase and solvents, matrix effects, recovery, sensitivity and compound resolution. Baseline separation was achieved for the five underivatized analytes both in GC and LC. The LC/MS/MS technique was more suitable for the analysis of urine samples, being less influenced by matrix effects and showing excellent sensitivity and selectivity. A preliminary application of the reported method for the diagnosis of metabolic diseases was also described. The determination of each analyte in its free form, described for the first time in the paper, offers new perspectives in the application of glucocorticoid analysis for diagnostic purposes. Copyright © 2009 John Wiley & Sons, Ltd. [source] Phospholipids in liquid chromatography/mass spectrometry bioanalysis: comparison of three tandem mass spectrometric techniques for monitoring plasma phospholipids, the effect of mobile phase composition on phospholipids elution and the association of phospholipids with matrix effectsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2009Yuan-Qing Xia Because plasma phospholipids may cause matrix effects in bioanalytical liquid chromatography/tandem mass spectrometry (LC/MS/MS) methods, it is important to establish optimal mass spectrometric techniques to monitor the fate of phospholipids during method development and application. We evaluated three MS/MS techniques to monitor phospholipids using positive and negative electrospray ionization (ESI). The first technique is based on using positive precursor ion scan of m/z 184, positive neutral loss scan of 141 Da and negative precursor ion scan of m/z 153. The second technique is based on using class-specific positive and negative selected reaction monitoring (SRM) transitions to monitor class-representative phospholipids. The third technique, previously reported, utilizes in-source collision-induced dissociation (CID)-based positive SRM of m/z 184,,,184. We recommend the all-inclusive technique 1 for use in qualitative assessment of all classes of phospholipids and technique 2 for use in quantitative assessment of class-representative phospholipids. Secondly, we evaluated the elution behaviors of the plasma phospholipids under different reversed-phase mobile phase conditions. The phospholipid-eluting strength of a mobile phase was mainly dependent on the type and amount (%) of the organic eluent and the strength increased in the order of methanol, acetonitrile and isopropyl alcohol. Under the commonly used gradient and isocratic elution schemes in LC/MS/MS bioanalysis, not all the phospholipids are eluted off the column. Thirdly, we investigated the association between phospholipids and matrix effects in positive and negative ESI using basic, acidic and neutral analytes. While the phospholipids caused matrix effects in both positive and negative ESI, the extent of ionization suppression was analyte-dependent and was inversely related to the retention factor and broadness of the phospholipids peaks. The lysophospholipids which normally elute earlier in reversed-phase chromatography are more likely to cause matrix effects compared to the later-eluting phospholipids in spite of the larger concentrations of the latter in plasma. Copyright © 2009 John Wiley & Sons, Ltd. [source] Simultaneous determination of parabens, triclosan and triclocarban in water by liquid chromatography/electrospray ionisation tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2009Iria González-Mariño A method for the determination of several household biocides in water by liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI-MS/MS) is presented. It permits the simultaneous determination of triclosan (TCS), triclocarban (TCC) and seven parabens, including the distinction between branched and linear isomers of propyl (i -PrP and n -PrP) and butyl parabens (i -BuP and n -BuP). Prior to LC/MS/MS, analytes are preconcentrated by solid-phase extraction (SPE) on Oasis HLB (60,mg) cartridges at natural sample pH and subsequently eluted with 4,mL of methanol. This simple SPE procedure provides extraction recoveries above 85% except for raw wastewater, where it falls to 65% for TCC. The performance of the method was tested with two triple-quadrupole LC/MS instruments from a low/mid and mid/high market range: a Varian 1200L and an API-4000. The latter system provided between 3 and 80 times lower limits of quantification (LOQs) than the first one, in the 0.08,0.44,ng/L range for surface water. Moreover, a comparison of matrix effects on both instruments showed a very different behaviour, particularly in the case of parabens. For these compounds signal suppression was observed in the 1200L instrument and signal enhancement with the 4000 instrument. As a result, different calibration approaches were chosen for them and this pointed to the need of matrix effect re-evaluation in method transfer between different LC/MS systems. The application of the method to real samples showed the ubiquity of methyl paraben (MeP) and n -PrP (at the 1,6,µg/L in raw wastewater) and the coexistence of i -BuP and n -BuP at similar levels (ca. 100,200,ng/L in raw wastewater). 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