Home About us Contact
|
Home About us Contact | ||
|
|
||
Quantification Limit (quantification + limit)
Selected AbstractsIon-pairing reversed-phase liquid chromatography/electrospray ionization mass spectrometric analysis of 76 underivatized amino acids of biological interest: a new tool for the diagnosis of inherited disorders of amino acid metabolismRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2005Monique Piraud Seventy-six molecules of biological interest for the diagnosis of inherited disorders of amino acids (AA) metabolism have previously been demonstrated to be detectable in electrospray ionization tandem mass spectrometry (ESI-MS/MS) positive mode without derivatization. Reversed-phase liquid chromatography (RPLC) separation on different C18 columns using various perfluorinated carboxylic acids as ion-pairing agents has been found suitable for coupling with MS/MS, and for the separation of AA. A new procedure was optimized in order to replace the usual ion-exchange chromatographic, post-column ninhydrin derivatization, time-consuming routine method. This procedure allowed an adequate separation of all the molecules from other known interfering compounds, and a throughput of two samples per hour. Quantification limits for each molecule were found to be compatible with their measurement in plasma and urine. We validated the qualitative part of the method by analyzing plasma and urine samples from patients affected with several inherited disorders of AA metabolism. We validated the quantification of 16 AA using their stable isotopes as internal standard. The calibration curves were linear over the range 0,3,mM. The quantitative results obtained with the new method on 105 plasma and 99 urine samples were in good agreement with those obtained by the established routine method. Spiking experiments and precision results were also satisfactory. Copyright © 2005 John Wiley & Sons, Ltd. [source] Electrocatalytic Reduction of Nitrite Ion on a Toluidine Blue Sol-Gel Thin Film Electrode Derived from 3-Aminopropyl Trimethoxy SilaneELECTROANALYSIS, Issue 22 2007K. Thenmozhi Abstract An organically modified sol-gel electrode using 3-aminopropyltrimethoxy silane for covalent immobilization of a redox mediator namely toluidine blue has been reported. Cyclic voltammetric characterization of the modified electrode in the potential range of 0.2,V to ,0.6,V exhibited stable voltammetric behavior in aqueous supporting electrolyte with a formal potential of ,0.265,V vs. SCE, corresponding to immobilized toluidine blue. The electrocatalytic activity of the modified electrode when tested towards nitrite ion exhibited a favorable response with the electrocatalytic reduction of nitrite occurring at a reduced potential of ,0.34,V. A good linear working range from 2.94×10,6,M to 2.11×10,3,M with a detection limit of 1.76×10,6,M and quantification limit of 5.87×10,6,M was obtained for nitrite determination. The stable and quick response (4,s) of the modified electrode towards nitrite under hydrodynamic conditions shows the feasibility of using the present sensor in flow systems. Significant improvements in the operational stability by overcoming the leachability problem and repeatability with a relative standard deviation of 1.8% of the TB thin film sensor have been obtained by the strategy of immobilization of the mediator in the sol-gel matrix. [source] Quantification of free and esterified steryl glucosides in vegetable oils and biodieselEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 8 2009Florence Lacoste Dr. Abstract Steryl glucosides (SG) are minor components that dramatically modify the low temperature performance of fatty acid methyl esters (FAME) used as biodiesel. SG are naturally present in vegetable oils but they may also be the result of the transesterification of esterified steryl glucosides (ESG). These are present in vegetable oils at a level of a few hundred milligrams per kilogram, depending on the nature of the feedstock. We developed an analytical method to quantify SG and ESG in vegetable oils and in FAME. The purification of SG and ESG was performed by liquid chromatography on silica gel, and the analysis of the trimethylsilyl derivatives was achieved by gas chromatography and flame ionization detection. The filterability of biodiesel is affected when the SG content is higher than 20,mg/kg. Therefore, the sensitivity of this new method is adapted for this purpose since the quantification limit is 10,mg/kg of SG and ESG. The recoveries are acceptable, between 75% and 90% depending on the species and content, and the reproducibility relative standard deviation, evaluated at 10%, is comparable to other studies. [source] Free Amino Acids in Botanicals and Botanical PreparationsJOURNAL OF FOOD SCIENCE, Issue 5 2008B. Carratů ABSTRACT:, Numerous studies were carried out about aminoacidic composition of vegetable proteins, but information about the free amino acid pool and the role of these substances is very incomplete. The aim of this paper was to contribute to the scarce knowledge concerning the composition of free amino acids in botanicals and botanical preparations widely used as food, in dietary supplements, and in pharmaceutical products. This work studied the composition of free amino acids, identified the major components of 19 species of plants, and evaluated the influence of different types of extraction on the amino acid profile. Amino acids were determined using an automatic precolumn derivatization with fluorenylmethyl-chloroformate and reversed-phase liquid chromatography with fluorescence and ultraviolet detection. The amounts of total free amino acids varied widely between plants, from approximately 12 g in 100 g of Echinacea pallida extract to less than 60 mg in the same amount of Coleus forskohlii, Garcinia cambogia, and Glycine max. In 13 plants arginine, asparagine, glutamine, proline, and ,-aminobutyric acid were the free amino acids found in preponderant quantities. The levels of free amino acids above the quantification limit in 36 assayed samples of botanicals, extracts, and supplements are shown. [source] High concentrations of the melatonin metabolite, N1 -acetyl- N,2 -formyl-5-methoxykynuramine, in cerebrospinal fluid of patients with meningitis: a possible immunomodulatory mechanismJOURNAL OF PINEAL RESEARCH, Issue 3 2005Sueli De Oliveira Silva Abstract:, We evaluated the presence of the melatonin metabolite N1 -acetyl- N2 -formyl-5-methoxykynuramine (AFMK), in cerebrospinal fluid (CSF) of patients with viral meningitis (n = 20) and control samples (n = 8) and correlate AFMK levels with inflammatory markers such as cellularity, protein, tumor necrosis factor (TNF)- ,, interleukin (IL)-8 and IL-1, levels. A portion of the CSF was extracted with dichloromethane (1:5) and analyzed by high-performance liquid chromatography (HPLC) under standardized conditions for AFMK. AFMK was detected in 16 of 20 CSF samples of patients with viral meningitis; the concentration of AFMK was found to be above the quantification limit (50 nmol/L) in six of these samples. AFMK was not detected in any of the eight control samples. The samples were classified into groups according to AFMK levels: undetectable (<10 nmol/L, group I), detectable but below the quantification limit (< 50 nmol/L, group II), and quantified (>50 nmol/L, group III). Group II presented the highest levels of proteins and IL-8, whereas group III showed the lowest levels of the inflammatory parameters. This study supports our hypothesis that inflammation favors the formation of AFMK and that this compound has immunomodulatory activity in vivo. [source] Quantitative determination of haloperidol in tablets by high performance thin-layer chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 5 2007Sigrid Mennickent Abstract A densitometric high performance thin-layer chromatography (HPTLC) method was developed and validated for the quantitative analysis of haloperidol in tablets. Chromatographic separation was achieved on precoated silica gel F 254 HPTLC plates using a mixture of acetone/chloroform/n -butanol/acetic acid glacial/water (5:10:10:2.5:2.5 v/v/v/v/v) as the mobile phase. Quantitative analysis was carried out at a wavelength of 254 nm. The method was linear in the 10,100 ng/,L range, with a determination coefficient of 0.999. The coefficients of variation for precision were not higher than 2.35%. The detection limit was 0.89 ng/,L, and the quantification limit was 2.71 ng/,L. The accuracy ranged from 97.76 to 100.33%, with a CV not higher than 4.50%. This method was successfully applied to quantify haloperidol in real pharmaceutical samples, including the comparison with HPLC measurements. The method was fast, specific, with a good precision and accuracy for the quantitative determination of haloperidol in tablets. [source] Quantitative assay of plasma homocysteine thiolactone by gas chromatography/mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 4 2003Parham Daneshvar Enzymatic cyclization of homocysteine forms a reactive thiolactone that may play an important role in its cardiovascular toxicity, but reliable quantitation of the free thiolactone metabolite in physiological fluids has not been reported. We have therefore used a highly selective gas chromatography/mass spectrometry (GC/MS) technique combined with the sensitivity of negative chemical ionization (NCI) to develop a quantitative method for the detection of homocysteine thiolactone (HcyTL) in plasma. To improve accutacy the deuterated isomer d4 -HcyTL was synthesized and added to plasma as internal standard. The plasma was then treated with silica solid-phase extraction and derivatized with heptafluorobutyric anhydride. The derivative was analyzed by GC/MS in NCI mode with methane as the reagent gas and quantified by analyzing for the HcyTL ion [M, HF] and its d4 -HcyTL counterpart in single-ion monitoring mode. The calibration curve showed a dynamic linear range up to 40 nmol/L. Within-day precision (n,=,20, nominal concentration 5.2 nmol/L) was 0.96% and between-day precision was 3.9%, with a detection limit of 1.7 nmol/L and quantification limit of 5.2 nmol/L. Two human plasma samples had HcyTL concentrations of 18 and 25 nmol/L. This facile method for quantitation of homocysteine thiolactone opens the way for more detailed clinical studies of its potential role in homocysteine-induced arteriosclerosis and vaso-occlusive disease. Copyright © 2003 John Wiley & Sons, Ltd. [source] Rapid determination of short-chain fatty acids in colonic contents and faeces of humans and rats by acidified water-extraction and direct-injection gas chromatographyBIOMEDICAL CHROMATOGRAPHY, Issue 8 2006Guohua Zhao Abstract Short-chain fatty acids (SCFAs) have attracted much attention recently because of their positive physiological effects. In this work, a rapid and reliable gas chromatographic method for determination of eight SCFAs, in colonic and faecal samples from rats and humans has been developed and validated. The methodology involves extraction of the SCFAs in water before a direct injection procedure on a FFAP capillary column. A stock standard solution containing acetic acid, propionic acid, n -butyric acid, i -butyric acid, n -valeric acid, i -valeric acid, n -caproic acid and n -heptanoic acid was prepared and used. A high line-arity (r2 > 0.9990), low quantification limit (2.38,30.14 µm) and high recovery for most acids were obtained. Acidification of faecal samples was found to be crucial for quantitative determination of the SCFAs, and adjustment of pH to 2,3 was regarded as necessary. Glass wool inserted in the glass liner of the injection port proved effective in preventing the contamination of the column by non-volatiles, and 12% formic acid reduced the ghost peak that appeared gradually after several injections. After validation, the methodology was applied on two faecal samples from rats fed diets containing different amount of dietary fibre and one faecal sample from human fed a normal diet to test the accuracy of the developed method. Copyright © 2005 John Wiley & Sons, Ltd. [source] Effect of age and single versus multiple dose pharmacokinetics of letrozole (Femara®) in breast cancer patientsBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 5 2001Christian U. Pfister Abstract Letrozole (trademark Femara®) is a new orally active, potent and selective aromatase inhibitor for the hormonal treatment of advanced breast cancer in postmenopausal women. The pharmacokinetics of letrozole and the suppression of peripheral estrogens were studied in 28 breast cancer patients after a single dose and at steady state. The pharmacokinetics of two distinct age groups (,50, ,65, N=15 and ,70 years old, N=9) were compared. There were no significant differences in area under the curve (AUC) or terminal half-life between the two age groups neither after a single dose nor at steady state. However, when comparing steady state to single dose kinetics, half-life and AUC increased significantly by 42% (90% CI: 1.13, 1.78) and 28% (90% CI: 1.12, 1.47), respectively. This deviation from linearity was probably due to a partial saturation or auto-inhibition of the dominant metabolic clearance mechanism of letrozole. At steady state, approximately 70% of the administered dose was excreted in urine as unchanged letrozole (6.0±3.8%) or as the glucuronide of the major, pharmacologically inactive metabolite CGP44645 (64.2±22.7%). A single dose of letrozole caused suppression of serum estrogen levels close to the quantification limit of the assay. No difference between single dose suppression and suppression at steady state could be detected. Copyright © 2001 John Wiley & Sons, Ltd. [source] Improved RP-HPLC determination of quinine in plasma and whole blood stored on filter paperBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 9 2000J.A. Kolawole Abstract Analysis of quinine in plasma and whole blood samples dried on filter paper is described. Sample preparation involves liquid extraction of plasma and whole blood from the filter paper and subsequent solid-phase extraction using C8 Bond Elut cartridges. A reverse-phase liquid chromatography system with UV detection and fluorescence detection was used. The analytical characteristics of the method are reported, with a quantification limit of 0.1 µg mL,1 and within an assay coefficient of variation of 5.6,8.4% in plasma and 6.5,12% in whole blood. Representative chromatograms are shown as a function of time for samples from human subjects after ingestion of a single 400-mg dose of quinine sulphate. Quinidine, dihydroquinine and metabolites are well separated from quinine with a resolution of above 1 (Rs>1). Copyright © 2000 John Wiley & Sons, Ltd. [source] Bismuth Film Electrode as an Alternative for Mercury Electrodes: Determination of Azo Dyes and Application for Detection in Food StuffsELECTROANALYSIS, Issue 21 2007Benoît Claux Abstract Bismuth electrodes were investigated and exhibit electrochemical properties similar to mercury electrodes but with much lower toxicity. An electrochemical application of bismuth film modified glassy carbon electrode for azo dyes determination was investigated. The plating step was optimized in order to achieve its analytical efficiency. A plating potential of ,0.9,V in a solution of 200,mg/L Bi(NO3)3, 0.5,M HNO3 for 100,s yields to a suitable electrode (in terms of stability and detection). Azo dyes such as azorubine (i.e., carmoisine, E122), amaranth (E123), ponceau 4R (i.e., new coccine, E124) and allura red (E129) were determined by differential pulse voltammetry in a NaCl solution in the concentration range of few ppm to 100 ppm. The reproducibility of the signal, characterized by the relative standard deviation, was found to be less than 5%, the detection and quantification limits were few mg/L. The influence of other food components on the signal was studied and the applicability was tested on real beverages samples. [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] Use of liquid chromatography,tandem mass spectrometry for quantitative analysis of clopyralid in compost and forageGRASSLAND SCIENCE, Issue 3 2009Ryuichi Uegaki Abstract In this study, we first developed a technique to quantify clopyralid using liquid chromatography,tandem mass spectrometry (LC/MS/MS) and tested its performance for compost and corn plant samples. Then, we measured the uptake of clopyralid by forage corn grown on two types of soil mixed with clopyralid-contaminated compost, in order to investigate the potential of ingestion of compost clopyralid by animals through forage crops. Because of the high recovery ratios (80,82% for compost and 98% for corn), sufficient theoretical quantification limits (5.0 and 1.7 ,g kg,1 fresh matter, respectively) and close agreement with the bioassay method (73 ,g kg,1 for LC/MS/MS and 80 ,g kg,1 for bioassay), the LC/MS/MS method was considered to be of potential value for determining clopyralid in compost and plant materials. Corn plants took up clopyralid from soil (compost), with the amount and rate of uptake varying with soil types and application of activated carbon to soil. There is a need for quantifying clopyralid uptake by a range of forage crops under a range of cultivation conditions (e.g. climate, soil, management) to estimate clopyralid fluxes through the manure,forage,animal,manure pathway. [source] Detection of drug-resistant HIV minorities in clinical specimens and therapy failureHIV MEDICINE, Issue 3 2008S Louvel Objective Particularly for therapy-experienced patients, resistance assessment by genotypic or phenotypic methods produces discordances. This study seeks proof that differences may arise from the fact that genotyping produces a single summary sequence whereas replicative phenotyping (rPhenotyping) functionally detects and assigns resistances in mixed HIV populations. Methods For validation, defined mixes of wild-type and M184V mutant were analysed by rPhenotyping or standard genotyping. Allele-specific and quantitative polymerase chain reaction (PCR) set detection and quantification limits for minor virus populations in vitro and in authentic clinical samples showing geno-/pheno-discrepant lamivudine resistance. Results Allele-specific and real-time PCR methods detected down to 0.3% of mutant M184V. The functional assessment was sensitive enough to reveal <1% of mutant M184V in mixed samples. Also in discordant samples from the diagnostic routine, in which rPhenotyping had identified drug resistance, real-time PCR confirmed minute amounts of mutant M184V. Conclusion By utilizing the replication dynamics of HIV under drug pressure, a rPhenotyping format potently reveals relevant therapy-resistant minority species, even of HIV known to possess reduced replicative fitness. With its rapid turnaround of 8 days and its high sensitivity, our rPhenotyping system may be a valuable diagnostic tool for detecting the early emergence of therapy-threatening HIV minorities or the persistence of residual resistant virus. [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] Silica-based monolithic column with evaporative light scattering detector for HPLC analysis of bacosides and apigenin in Bacopa monnieriJOURNAL OF SEPARATION SCIENCE, JSS, Issue 15-16 2009Pamita Bhandari Abstract A high performance liquid chromatographic method using a silica-based monolithic column coupled with evaporative light scattering detector (HPLC,ELSD) was developed and validated for simultaneous quantification of bacosides (bacoside A, bacopaside I, bacoside A3, bacopaside II, bacopaside X, bacopasaponin C) and apigenin in Bacopa monnieri. The chromatographic resolution was achieved on a Chromolith RP-18 (100×4.6 mm) column with acetonitrile/water (30:70) as mobile phase in isocratic elution at a flow rate of 0.7 mL/min. The drift tube temperature of the ELSD was set to 95°C, and the nitrogen flow rate was 2.0 SLM (standard liter per minute). The calibration curves revealed a good linear relationship (r2 >0.9988) within the test ranges. The detection limits (S/N = 3) and the quantification limits (S/N = 10) for the compounds were in the range of 0.54,6.06 and 1.61,18.78 ,g/mL, respectively. Satisfactory average recovery was observed in the range of 95.8,99.0%. The method showed good reproducibility for the quantification of these compounds in B. monnieri with intra- and inter-day precision of less than 0.69 and 0.67%, respectively. The validated method was successfully applied to quantify analytes in nine accessions of B. monnieri and thus provides a new basis for overall quality assessment of B. monnieri. [source] Two-dimensional coordination polymer matrix for solid-phase extraction of pesticide residues from plant Cordia salicifoliaJOURNAL OF SEPARATION SCIENCE, JSS, Issue 12 2009Pedro Henrique Viana de Carvalho Abstract The 2D coordination polymer (,[Gd(DPA)(HDPA)]) was tested for extraction of acephate, chlorpropham, pirimicarb, bifenthrin, tetradifon, and phosalone from the medicinal plant Cordia salicifolia, whose extracts are commercialized in Brazil as diuretic, appetite suppressant, and weight loss products, using GC/MS, SIM. Considering that there are no Brazilian regulations concerning maximum permissible pesticide residue concentrations in medicinal herbs, recovery experiments were carried out (seven replicates), at two arbitrary fortification levels (0.5 and 1.0 mg/kg), resulting in recoveries in range of 20 to 107.7% and SDRSDs were between 5.6 and 29.1% for ,[Gd(DPA)(HDPA)] sorbent. Detection and quantification limits for herb ranged from 0.10 to 0.15 mg/kg and from 0.15 to 0.25 mg/kg, respectively, for the different pesticides studied. The developed method is linear over the range assayed, 0.5,10.0 ,g/mL, with correlation coefficients ranging from 0.9975 to 0.9986 for all pesticides. Comparison between ,[Gd(DPA)(HDPA)] sorbent and conventional sorbent (neutral alumina) showed similar performance of ,[Gd(DPA)(HDPA)] polymeric sorbent for three (bifenthrin, tetradifon, and phosalone) out of six pesticides tested. [source] Validated liquid chromatographic method for quantitative determination of allicin in garlic powder and tabletsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 16 2007Marta de Diego Abstract In the present study, an RP high performance liquid chromatographic method was developed and validated for the determination of allicin in garlic powder and tablets. Chromatographic separation was carried out on an RP-18e column (125 mm×4 mm), using a mobile phase, consisting of methanol,water (50:50 v/v), at a flow rate of 0.5 mL/min and UV detection at 220 nm. Ethylparaben was used as the internal standard. The assay was linear for allicin concentrations of 5.0,60.0 ,g/mL. The RSD for precision was <6.14%. The accuracy was above 89.11%. The detection and quantification limits were 0.27 and 0.81 ,g/mL, respectively. This method was used to quantify allicin in garlic powder samples. The results showed that the method described here is useful for the determination of allicin in garlic powder and tablets. [source] In-house validation of a high-performance liquid chromatography analytical method for quantification of ochratoxin A in unfermented grape juiceJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 11 2007Ma Teresa Murillo Abstract A validated high-performance liquid chromatography (HPLC) method with fluorescence detection for the quantitative analysis of ochratoxin A (OTA) in unfermented grape juice is described. Five millilitres of unfermented grape juice was mixed with 45 mL of PBS, and the pH was adjusted to 7.2. Then the mixture was filtered under vacuum through a glass microfibre filter and cleaned up with immunoaffinity columns prior to analysis by HPLC. Validation of the analytical method was based on the following criteria: selectivity, linearity, limit of detection and quantification, precision (within-day and between-day variability) and recovery and uncertainty estimation. Detection and quantification limits obtained were 0.02 µg L,1 and 0.05 µg L,1 respectively. The percentage recovery was 91.5% (RSD = 3.9). This method was applied to the measurement of 30 veraison stage unfermented grape juice samples. Copyright © 2007 Society of Chemical Industry [source] | ||||||||||||||||||||||||||||