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At least 19 recordsLinked to original sources
PubMed1995

Sample pretreatment with nitrate reductase and glucose-6-phosphate dehydrogenase quantitatively reduces nitrate while avoiding interference by NADP+ when the Griess reaction is used to assay for nitrite.

An assay for the simultaneous measurement of nitrite and nitrate, products of nitric oxide metabolism, is described. Others have reported pretreating sample by using nitrate reductase (NR) and NADPH to reduce endogenous NO3- before assaying the resultant NO2- using the Griess reaction. However, we found that the NADP+ formed during pretreatment interfered with the Griess reaction when NADPH was used at concentrations necessary to drive the NR reaction. For instance, 500 microM NADP+ in 100 microM NaNO3- (without NR) causes a 90% interference with the formation of Griess reaction product. To limit interference, we modified the method by decreasing the NADPH concentration to 1 microM. NADPH was regenerated by coupling the NR reaction with that catalyzed by glucose-6-phosphate dehydrogenase (GD). Using this method, NaNO3- standard curves were linear up to 100 microM and coincided with control curves obtained using NaNO2- incubated in parallel. Addition of urine up to a strength of 20% did not interfere with the assay. Comparison with an alternative assay based on cadmium reduction resulted in the following linear regression: [Cd method] = 0.915*[NR-GD method] + 0.37, r2 = 0.997. Coupling GD to NR to recycle NADPH allows this cofactor to be used at a low concentration so that interference with the Griess reaction is negligible.

Animals↗
PubMed2004

Miniaturized and automated sample pretreatment for determination of PCBs in environmental aqueous samples using an on-line microporous membrane liquid-liquid extraction-gas chromatography system.

A new, fast, and automated sample pretreatment technique for determination of lipophilic organic compounds in aqueous samples has been developed and applied to the determination of polychlorinated biphenyls (PCBs) in environmental river water. It is based on miniaturized microporous membrane liquid-liquid extraction coupled on-line to gas chromatography (GC) with electron capture detection. The heart of the system that simultaneously connects the sample pretreatment step to the final GC analysis has been named the extracting syringe (ESy). The ESy carries a miniaturized membrane extraction card attached to an electrically and mechanically designed installment and is mounted directly over a GC injector for fully automated injection of the extract. A method was developed to extract 10 PCB congeners from 1-mL water samples (after addition of 40% acetonitrile) with an extraction time of 10 min. The optimized methodology showed good linearity (in the dynamic concentration range of 5 ng L(-)(1)-1 microg L(-)(1)), enrichment factors of 33-40 times, repeatable extractions (RSD 2-5%, n = 4), and low detection limits (2-3 ng L(-)(1)). Acetonitrile had to be added to the samples in order to overcome the influence of PCB adsorption on the repeatability of extraction and enrichment and to minimize the overall memory effect (OME). OME and carryover depended not only on the concentration of the organic solvent added to the sample and that used in the washing procedure but also on whether the extracting card was changed or not. When an optimized washing procedure was applied, the OME was approximately 0.2% at high concentrations (i.e., 1 microg L(-)(1)). When each extraction took place in a new extraction card, no OME was detected. Additionally, no significant adsorption onto glass surfaces or a matrix effect on extraction was noticed. The main features of this methodology are good extraction repeatability, low detection limits at short extraction time, and the unsurpassed characteristic of no detectable OME in the entire system when each sample is processed in a new card. The total consumption of organic (nonchlorinated) solvents is less than 5 mL per sample.

Journal Article↗
PubMed1997

Automated on-line sample pretreatment system for the determination of trace metals in biological samples by inductively coupled plasma mass spectrometry.

A fully automated on-line sample pretreatment system combining microwave digestion with sample preconcentration/matrix separation for the determination of trace metals (Fe, Ni, Cu, Zn, and Pb) in blood and serum samples by inductively coupled plasma mass spectrometry (ICPMS) was designed and evaluated. The samples were mixed with an appropriate reagent and digested in a flow-through, focused microwave-heated oven. After digestion, the sample solution was transferred on-line to a column packed with iminodiacetate-based resin for separation of matrix elements like Na, K, Ca, Mg, Cl, P, and S that might interfere with the measurement by ICPMS. The analytes chelated on the resin were subsequently eluted and led to ICPMS for multielement determination. The whole sample pretreatment process was automatically controlled by a self-designed expert system. The analytical reliability of data from this on-line system was confirmed to be good with the analysis of SRM samples (Seronorm Whole Blood and NIST SRM 1598 Bovine Serum), and the limits of detection (3 sigma) for Fe, Ni, Cu, Zn, and Pb were 68, 0.34, 3.5, 13.4, and 0.22 microgram/L, respectively. With this fully automated on-line system, the determination of analytes in biological fluid samples down to micrograms-per-liter levels has been proven to be feasible, and the sample throughput can achieve up to 6 samples/h.

Animals↗
PubMed2000

Use of nitric acid in sample pretreatment for determination of trace elements in various biological samples by ETAAS.

Trace elements in liquid biological samples may be determined by direct electrothermal atomic absorption spectrometry (ETAAS). In our previous work it was found that samples containing proteins or DNA may leak out of the graphite tube before the drying step, despite the addition of various modifiers. In order to keep the sample to the graphite tube, samples were diluted before analysis 1 + 1 with 32% v/v nitric acid, or 5 microl of 32% v/v nitric acid was added to the graphite tube before ETAAS determination. Applying the proposed procedure, the concentrations of lead in eluted fractions after gel chromatographic separation of human cerebellar nucleus dentatus supernatant and platinum in isolated DNA samples were determined. The use of nitric acid in sample pretreatment prevent sample leakage out of the graphite tube, provided for even drying and considerably reduced nonspecific absorption in lead determination. The repeatability of measurements was better than + 6%. The accuracy of the procedure was checked by spiking samples. The recoveries for both elements lay between 93--104%. Nitric acid was found to be a better modifier than TRITON X-100.

Calibration↗
PubMed2003

Capillary isotachophoresis of cystine in urine with on-line isotachophoresis sample pretreatment.

Capillary isotachophoresis (ITP) with on-line isotachophoresis sample pretreatment and conductivity detection has been proposed as a method for the separation, detection and determination of cystine present in urine. Sample pretreatment was achieved using a 90 mm FEP capillary tube with a 800 microm internal diameter. ITP separations and conductivity detection were carried out in a 160 mm capillary tube with a 300 microm internal diameter, filled with a hydrochloric acid leading electrolyte and glycine terminating electrolyte, at 50 microA and 25 degrees C. The results show that the proposed method is suitable for resolution of cystine from matrix interferents present in the urine samples and is able to detect it at 10(-4) mol/l concentrations by a universal detection technique after removal of a significant part of the anionic constituents of the sample migrating in the on-line coupled capillary isotachophoresis stack. This simple ITP procedure for monitoring cystine in urine samples requires no sample preparation. This makes it an alternative to the currently used procedures.

Adult↗
PubMed1984

Systematic comparison of three basic methods of sample pretreatment for high-performance liquid chromatographic analysis of antiepileptic drugs using gas chromatography as a reference method.

Sera of epileptic patients which were routinely examined by gas chromatography (GC) were also analysed using high-performance liquid chromatography (HPLC). Three basic methods for the pretreatment of samples for HPLC analysis were compared: protein precipitation by adding acetonitrile to the serum, direct serum extraction using ethylacetate, and partitioning of serum and buffer solution over a stationary phase and extraction with dichloromethane/2-propanol. The analytical performance and practicability of the three methods were tested under routine conditions. The following anti-epileptic drugs and metabolites were used in the comparison of HPLC with GC: ethosuximide, primidone, phenobarbital, phenytoin, carbamazepine, N-desmethylmethsuximide, and phenylethylmalonediamide.

Anticonvulsants↗
PubMed1995

Biocompatible sample pretreatment for immunochemical techniques using micellar liquid chromatography for separation of corticosteroids.

Micellar liquid chromatography (MLC) using Tween 20 as surfactant was evaluated as a biocompatible sample pretreatment preceding immunoassay in order to obtain an increased selectivity of the assay and a simplification of the sample pretreatment procedure. Different stationary phases and chromatographic conditions were studied for the separation of budesonide and cortisol and some steroids known to interfere in immunoassay of these compounds. The separation was dependent on several parameters, for example, temperature, the concentration of Tween 20, pH and ionic strength of the mobile phase, and nature of the stationary phase. A precolumn venting system was used, which allowed for 140 direct injections of 25 microliters of human blood plasma, without loss of chromatographic performance. Results obtained from the coupling of MLC to an immunoassay for cortisol illustrates the selectivity which can be obtained, and that simplification of the sample pretreatment is possible using this technique.

Adrenal Cortex Hormones↗
PubMed2001

Capillary zone electrophoresis of orotic acid in urine with on-line isotachophoresis sample pretreatment and diode array detection.

Potentialities of capillary zone electrophoresis with on-line isotachophoresis sample pretreatment and diode array detection (ITP-CZE-DAD) to the separation, detection and identification of trace analytes present in biological matrices were investigated. Urine represented a multicomponent, variable and high ionic strength matrix while orotic acid was chosen as a model analyte of a practical clinical relevance in this investigation. Using the ITP-CZE combination in the column-coupling configuration of the separation system ITP provided an enhanced sample load capacity to the separation system (a 30 microl sample injection volume), concentrated the analyte and served as an on-line sample clean up technique. On the other hand, CZE performed a final separation of the analyte from matrix constituents present in the ITP pretreated sample and provided favorable conditions for its detection and identification by DAD. Using current correction and smoothing procedures analytically relevant DAD spectra of orotic acid could be obtained also in instances when this was injected in a model sample at a 2 x 10(-7) mol/l concentration (an estimated limit of determination of orotic acid at a 218 nm detection wavelength). ITP-CZE separations of urine samples (based on differences in acid-base properties and host-guest complexations of the analyte and matrix anionic constituents) led to significant sample clean ups. Consequently, DAD spectra of orotic acid matching its reference spectrum, could be acquired also in instances when the acid was present in urine matrices (loaded in 30 microl injection volumes of 20-fold diluted urine samples) at 4-6 x 10(-7) mol/l concentrations. Here, residual trace matrix interferents prevented a closer approach to the above value attainable for model samples. Although this work was focused only on one analyte and urine matrix it implies very promising potentialities of the ITP-CZE-DAD combination in the identification and quantitation of trace analytes present in biological matrices, in general.

Adult↗
PubMed1997

Capillary zone electrophoresis of nitrophenols with off-line isotachophoretic sample pretreatment.

Preparative capillary isotachophoresis (ITP) operating in a discontinuous fractionation mode was studied as a sample pretreatment technique for capillary zone electrophoresis (CZE) trace analysis of a group of ten nitrophenols. Different separation mechanisms employed by these capillary electrophoresis techniques made possible a group isolation of the studied analytes by ITP while their CZE resolutions based on differences in the interactions with polyvinylpyrrolidone (PVP) provided suitable conditions for a final analytical evaluation. Experiments with model and practical water samples revealed high and reproducible recovery rates of the ITP pretreatment of nitrophenols when sample loadability limits of the preparative ITP equipment were met. A main disadvantage of the studied ITP-CZE combination was an inefficient use of the pretreated sample as only 0.5% of the fraction containing nitrophenols was used in the final CZE step. Despite these limitations associated with the CZE sample injection, the concentration limit of detection (LOD) for nitrophenols in practical water samples could be reduced to 2-8 ppb concentrations (photometric absorbance detector operating at a 254 nm wavelength) when 200 microL sample volumes were taken for the ITP pretreatment. This was accompanied by an efficient sample clean-up as no other trace ionic constituents originating from the samples were detected on CZE.

Electrophoresis, Capillary↗
PubMed1998

A literature assessment of sample pretreatments and limits of detection for capillary electrophoresis of drugs in biological fluids and practical investigation with some antimalarials in plasma.

A literature survey on published reports of the determination of drugs in biological fluids shows that all methods of sample pretreatment have been used and that the limits of detection achieved vary widely, ranging from low ngcm(-3) to microgcm(-3). The most widely used injection method was hydrodynamic and, in the majority of cases, whenever low detection limits were achieved, this was a result of preconcentration during the sample pretreatment. Only a small proportion of the reported methods employed electrokinetic injection and utilised the field amplified sample injection (FASI) techniques. An experimental investigation of the alternative hydrodynamic and electrokinetic injection methods for a small set of antimalarial drugs is reported. It was found that electrokinetic injection with FASI from an acetonitrile-water matrix produced dramatic improvements in detection limits. This improvement could not, however, be achieved when the drugs were in plasma using protein precipitation, liquid-liquid extraction or solid phase extraction pretreatment methods. This highlights the importance of sample pretreatment in utilising the potential sensitivity of capillary electrophoresis with electrokinetic injection.

Antimalarials↗
PubMed1998

Influence of Cremophor EL on the quantification of paclitaxel in plasma using high-performance liquid chromatography with solid-phase extraction as sample pretreatment.

For the quantitative determination of paclitaxel in human plasma reversed-phase high-performance liquid chromatographic (HPLC) methods with solid-phase extraction (SPE) as sample pretreatment procedure are frequently used. Recovery problems arose during the quantification of paclitaxel in plasma samples of patients. The major problems were a large batch-to-batch difference in performance of the SPE columns and the effects of the pharmaceutical vehicle Cremophor EL on the performance of the SPE. Cremophor EL concentrations exceeding 1.0% (v/v) had a great impact on the absolute recovery of paclitaxel from human plasma with the SPE procedure. The recoveries decreased approximately 10 to 40% depending on the quality of the batch SPE columns. The problems are avoided by using 2'-methylpaclitaxel as the internal standard. This study points out the importance of including the effects of a pharmaceutical vehicle, like Cremophor EL, in the validation programme of a bioanalytical assay and the use of an internal standard in HPLC paclitaxel assays preceded by SPE as sample pretreatment procedure.

Antineoplastic Agents, Phytogenic↗
PubMed1995

Solid-phase extraction on Styrosorb cartridges as a sample pretreatment method in the stereoselective analysis of propranolol in human serum.

Sample pretreatment using solid-phase extraction (SPE) on cartridges filled with small-particle Styrosorb porous polystyrene-based sorbent has been used in the analysis of propranolol enantiomers in human serum by high-performance liquid chromatography (HPLC) with fluorescent detection. SPE on Sep-Pak C18 cartridges was used as a reference pretreatment method. The propranolol content of the samples was determined by achiral normal-phase HPLC and the enantiomeric ratio of propranolol (S/R) was then determined by chiral HPLC on a column with silica-bonded cellulose-tris(3,5-dimethylphenyl carbamate). Recoveries of propranolol from serum using SPE on Styrosorb and C18 phases were 97 +/- 5% and 96 +/- 5%, respectively. Detection and quantification limits for propranolol enantiomers were 4 and 7 ng/ml, respectively.

Chromatography, High Pressure Liquid↗
PubMed1982

Determination of dopamine and its acidic metabolites in brain tissue by HPLC with electrochemical detection in a single run after minimal sample pretreatment.

A method, based on reverse-phase liquid-liquid chromatography, has been developed for the determination, in a single run, of dopamine (DA) and its acidic metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), combined with electrochemical detection (ECD). If applied to brain tissue, sample pretreatment can be reduced to centrifugation, filtration and adjustment of pH and perchlorate concentration prior to introduction into the liquid chromatograph. The relation between the perchlorate (counterion) concentration of the mobile phase and the retention (k') of the amines is linear, as is the relation between the H+ concentration of the mobile phase and the retention of the acidic metabolites. This flexible phase system, combined with a simple and therefore reproducible sample pretreatment, warrants a high throughput of samples. The procedure offers good possibilities for routine analysis of catecholamines and their acidic metabolites in the picogram range. Some typical examples of the behaviour of this phase system and the electrochemical detector are presented and discussed.

Animals↗
PubMed2002

Analysis of polycyclic aromatic hydrocarbons in soil: minimizing sample pretreatment using automated Soxhlet with ethyl acetate as extraction solvent.

A simplified sample pretreatment method for industrially PAH-contaminated soils applying automated Soxhlet (Soxtherm) with ethyl acetate as extraction solvent is presented. Laborious pretreatment steps such as drying of samples, cleanup of crude extracts, and solvent exchange were allowed to be bypassed without notable performance impact. Moisture of the soil samples did not significantly influence recoveries of PAHs at a wide range of water content for the newly developed method. However, the opposite was true for the standard procedure using the more apolar 1:1 (v/v) n-hexane/acetone solvent mixture including postextraction treatments recommended by the U.S. EPA. Moreover, ethyl acetate crude extracts did not appreciably effect the chromatographic performance (HPLC-(3D)FLD), which was confirmed by a comparison of the purity of PAH spectra from both pretreatment methods. Up to 20% (v/v) in acetonitrile, ethyl acetate proved to be fully compatible with the mobile phase of the HPLC whereas the same concentration of n-hexane/acetone in acetonitrile resulted in significant retention time shifts. The newly developed pretreatment method was applied to three historically contaminated soils from different sources with extraction efficiencies not being significantly different compared to the standard procedure. Finally, the certified reference soil CRM 524 was subjected to the simplified procedure resulting in quantitative recoveries (>92%) for all PAHs analyzed.

Acetates↗
PubMed2003

Effects of organic solvents on sample pretreatment and separation performances in capillary electrophoresis.

A review of recent developments in theoretical as well as application studies concerning the use of organic solvents, either as purely nonaqueous solvents, hydro-organic mixtures, or a combination of an organic solvent with another organic modifier(s), in the sample matrix and/or separation buffer for effecting sample pretreatment and/or improving separation performances in capillary electrophoresis (CE) is presented. In particular, recent advances made in furthering the basic understanding of selectivity changes that occur in capillary zone electrophoresis due the presence of organic solvents in the separation medium, based on in-depth studies of fundamental processes, such as acid-base chemistry, ion-ion and ion-solvent interactions, were discussed in detail. The utilization of organic solvents for improving the resolution of highly challenging and important separations, i.e., those involving the separation of positional and optical isomers, was also critically reviewed. Furthermore, a comprehensive survey of the use of organic solvents for on-line sample pretreatment, e.g., minimizing aggregation and maximizing solubilization of hydrophobic analytes, improving concentration detection sensitivity for analytes via the use of sample stacking, was presented and discussed. Moreover, recent applications involving the use of organic solvents for improving the CE separations of a variety of molecular species with significance in various disciplines, including biological, environmental and pharmaceutical areas, were summarized and tabulated.

Electrophoresis, Capillary↗
PubMed1999

Micellar electrokinetic capillary chromatography as a powerful tool for pharmacological investigations without sample pretreatment: a precise technique providing cost advantages and limits of detection to the low nanomolar range.

A number of pharmaceuticals (e.g., acetaminophen, salicylic acid, sulfamethoxazole, theophylline, tolbutamide and trimethoprim) have been determined in human plasma by micellar electrokinetic chromatography (MEKC), without sample pretreatment, using underivatized fused-silica capillaries. The total analysis time was only 10 min. A sodium dodecyl sulfate (SDS)-containing borate buffer (60 mM with 200 mM SDS) at pH 10 was used. Between runs, proteins adsorbed to the capillary wall are removed by rinsing with SDS buffer and either acetonitrile (e.g., 50% v/v) or isopropanol (e.g., 10% v/v). Other rinsing procedures are discussed (salts, enzyme-containing solutions, organic solvents, sodium hydroxide, hydrofluoric acid). The separation system is tested in a concentration range between 10 ng/mL and 100 microg/mL; a detection limit of about 20 ng/mL can readily be obtained. The sensitivity was substantially improved using isopropanol as buffer additive. A day-to-day precision for relative peak areas of 1-2% relative standard deviation (RSD, n > 40) was reached in the upper concentration range. Under repeatability conditions, these values could also be obtained for low microg/mL concentrations. Thus, not only drug monitoring but also pharmacokinetic investigations from blood plasma become possible without further sample pretreatment.

Acetaminophen↗
PubMed1991

Bioanalysis of the neuropeptide des-enkephalin-gamma-endorphin by high-performance liquid chromatography with on-line sample pretreatment using gel permeation and solid-phase isolation.

A bioanalytical method is described that allows the determination of a number of beta-endorphin-related peptides. The method is based on the application of fluorescence detection after high-performance liquid chromatography followed by post-column derivatization with o-phthaldialdehyde. Concentrations exceeding 10-25 ng/ml could be determined by using conventional fluorescence detection, whereas lower concentrations demand the use of laser-induced fluorescence detection. The sample pretreatment includes the use of on-line gel permeation, on-line solid-phase isolation and heart cutting of a peak from reversed-phase gradient elution. The sample pretreatment procedure does not discriminate between the dodecapeptide des-enkaphalin-gamma-endorphin (DE gamma E) and its metabolites in order to obtain similar recoveries for all components. The final chromatographic phase system is based on ion-pair formation, which permits the separation of DE gamma E from its metabolites and degradation products. The optimized procedure allows the determination of these peptides in plasma at concentration levels down to about 1 ng/ml, demanding a sample volume of 1 ml.

Chromatography, Gel↗
PubMed1980

Effect of sample pretreatment on sorption of acetophenone by soils and sediments.

The effect of several sample pretreatment storage techniques, the effect of degree of grinding, and the effect or organic matter removal on the sorption of acetophenone was examined. No significant difference in the sorption of acetopheonone was observed when air-dried, freeze-dried, oven-dried, frozen, or samples kept at 2 degrees C (fresh) were compared. All pretreatment storage techniques resulted in linear sorption isotherms and gave good fits to the modified Freundlich equation (Cs = Kp . Cw). No significant differences in sorption constants (Kp) were observed for samples with a 2 mm maximum diameter when compared to samples ground to 0.6 mm maximum diameter or 0.25 mm maximum diameter. Organic matter removal resulted in decreased Kp values for samples containing more than 1% organic carbon initially but increased Kp values for samples containing less than 1% organic carbon before removal. Expandable 2:1 clay mineral content was significantly correlated with adsorption of acetophenone after organic matter removal.

Acetophenones↗