SEARCH · PubMed Health

Results for “Sample pretreatment”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21Linked to original sources

PubMed2005

Sample preconcentration with chemical derivatization in capillary electrophoresis. Capillary as preconcentrator, microreactor and chiral selector for high-throughput metabolite screening.

New strategies for integrating sample pretreatment with chemical analyses under a single format is required for rapid, sensitive and enantioselective analyses of low abundance metabolites in complex biological samples. Capillary electrophoresis (CE) offers a unique environment for controlling analyte/reagent band dispersion and electromigration properties using discontinuous electrolyte systems. Recent work in our laboratory towards developing a high-throughput CE platform for low abundance metabolites via on-line sample preconcentration with chemical derivatization (SPCD) is primarily examined in this review, as there have been surprisingly only a few strategies reported in the literature to date. In-capillary sample preconcentration serves to enhance concentration sensitivity via electrokinetic focusing of long sample injection volumes for lower detection limits, whereas chemical derivatization by zone passing is used to expand detectability and selectivity, notably for enantiomeric resolution of metabolites lacking intrinsic chromophores using nanolitre volumes of reagent. Together, on-line SPCD-CE can provide over a 100-fold improvement in concentration sensitivity, shorter total analysis times, reduced sample handling and improved reliability for a variety of amino acid and amino sugar metabolites, which is also amenable to automated high-throughput screening. This review will highlight basic method development and optimization parameters relevant to SPCD-CE, including applications to bacterial metabolite flux and biomarker analyses. Insight into the mechanism of analyte focusing and labeling by SPCD-CE is also discussed, as well as future directions for continued research.

Amino Acids↗

PubMed2026

Aflatoxins and their biosynthetic precursors in lotus seeds: simultaneous UPLC-MS/MS determination, contamination profiling, and matrix-specific accumulation during Aspergillus flavus infection.

Aflatoxin (AF) contamination poses a severe global threat to food and medicinal material safety, yet existing research focuses on terminal AF metabolites while neglecting residual biosynthetic precursors, leading to potential underestimation of contamination risks. In this study, a UPLC-MS/MS method was established for the simultaneous quantification of six AFs and their five precursors in lotus seeds, with optimization of mass spectrum parameters, chromatographic separation conditions, and sample pretreatment. Method validation confirmed linearity (R2 > 0.99), LODs (0.03-0.36 μg/kg), and recoveries (76.53%-120.0%, RSD < 15%). Analysis of 41 natural lotus seed samples revealed a 63.4% AF contamination rate, dominated by B-group AFs, while O-methylsterigmatocystin (OMST) and versicolorin hemiacetal (VOH) were identified as the primary co-residual precursors with co-occurrence rates ≥ 50%. Notably, AFM1 was predominantly detected in natural samples with AFB1 concentrations exceeding 100 μg/kg. Artificial inoculation experiments further demonstrated that sterilization and sealing conditions modulated AF biosynthesis in lotus seeds, with non-sterilized and non-sealed groups showing delayed fungal metabolism and lower toxin accumulation. A significant linear correlation was observed between AFM1 and AFB1 levels (r = 0.94) in infected samples, demonstrating their accumulation levels are coupled with fungal overall metabolic flux. Given the high co-occurrence rate of OMST/VOH with AFB1 in natural samples, their individual and combined toxicities require in-depth investigation. This work deciphers matrix-specific AF dynamics in lotus seeds, supporting regulatory standard refinement (e.g., precursor inclusion) and targeted control (e.g., time-sensitive drying after harvest). Further studies will focus on exploring the molecular mechanisms of substrate-dependent AF synthesis.

Aflatoxins↗

PubMed1985

Automated determination of amoxycillin in biological fluids by column switching in ion-pair reversed-phase liquid chromatographic systems with post-column derivatization.

Amoxycillin, a polar aminopenicillin, is rather unstable in biological fluids. Degradation can be prevented by fast sample pretreatment and storage at -70 degrees C or below. After pH adjustment, it is stable in biological fluids for over 16 h. The samples were handled by automated chromatography overnight. The chromatographic system consisted of a small guard column, two analytical columns separated by a switching valve, a post-column reactor and a fluorescence detector. The chromatographic events and the calculation of results were handled by a computing integrator. The chromatography was based on ion-pairing principles. An efficient clean-up of the biological fluids was obtained by a heart cut from the first column, where the neutral mobile phase contained hexyl sulphate. In the second column the organic anion was exchanged for a large quaternary ammonium compound; amoxycillin was then retained as an ion pair. The composition of the mobile phases had to be designed carefully in order to avoid a disturbance of the chromatographic performance on the last column. An adequate selectivity and sensitivity was obtained by a post-column derivatization with fluorescamine. Detection limits were 10 and 25 ng/ml for plasma and urine, respectively, and the inter-assay precisions at low levels (350 and 2000 ng/ml for plasma and urine, respectively) were ca. 5% (R.S.D.).

Amoxicillin↗

PubMed2002

Microsequential injection: anion separations using 'lab-on-valve' coupled with capillary electrophoresis.

Microsequential injection (microSI) has been successfully coupled with capillary electrophoresis (CE). Presented is the microSI-CE system, interfaced with an integrated Lab-on-Valve (LOV) manifold that provides an efficient sample delivery conduit and a versatile means of sample pretreatment along with total automation of the separation process. Programmable microSI protocols control all critical system peripherals to perform various types of CE sample injections automatically such as electrokinetic (EK) injection, hydrodynamic (HD) injection, and head column field amplification (HCFA) sample stacking injection. Novel features of the microSI-CE technique are demonstrated on assays of samples containing 10 anions that had been used previously as a model system. Calibration studies by EK sample injection yielded linear concentration ranges of 0.5-3.0 mM with linear regression responses of r2 = 0.9999 for both chloride and sulfate using conductivity corrected peak area (CCPA) as concentration responses. Calibration using an internal standard was studied at the same concentration range giving r2 = 0.9992 for both chloride and sulfate and r2 = 0.9997 for both when CCPA correction was deployed. With HCFA sample stacking injection, a linear concentration dynamic range of 0.034-3.419 mM for chloride and 0.014-1.408 mM for sulfate were produced with linear regression responses of r2 = 0.9999 for chloride and r2 = 0.9998 for sulfate.

Anions↗

PubMed1982

Changes in the proteins of wool following treatment of sheep with epidermal growth factor.

Administration of epidermal growth factor (EGF) extracted from mouse submaxillary gland to Merino sheep resulted in a temporary inhibition of the activity of the wool follicles. Subsequently, either complete discontinuities appeared in the fibers resulting in shedding of the entire fleece, or incomplete, in which case the fleece was retained but bore a zone of weakness. The protein composition of the first sample of wool harvested from 1 sheep following infusion for 66 hr with 27.5 mg EGF (0-2 weeks posttreatment) was similar to pretreatment wool. This represented wool fibers which were already present in the follicles at the beginning of infusion. Thereafter, the composition of the wool changed progressively, reaching a maximum divergence from the control in the 3-4 week regrowth period followed by a return to normal by about 10 weeks. Over this period the content of high-sulfur proteins first rose from an initial 19% to a maximum of 30%, then returned to 19%, while the high-tyrosine protein content initially decreased from 12% to 5% and then slowly increased to 12%. In addition to changes in overall protein composition, two-dimensional electrophoresis revealed alterations in the proportions of some individual protein components. These changes were similar to those observed with many other wool growth inhibitors. Smaller doses of EGF (5.8 and 2.9 mg but not 1 mg) had similar effects on wool composition but these were of lower magnitude and there was a delay in reaching a maximum response. Even after 16-18 weeks the wool from these treated sheep differed slightly in composition from the pretreatment samples.

Animals↗

PubMed1983

Simultaneous determination of tryptophan and its 5-hydroxy metabolites in human cerebrospinal fluid by reversed phase liquid chromatography with electrochemical detection.

A sensitive ion-pair reversed phase liquid chromatographic method for determining tryptophan, 5-hydroxytryptophan, 5-hydroxytryptamine (serotonin) and 5-hydroxyindole acetic acid has been developed. To separate these indoles in cerebrospinal fluid both octadecyl- and phenyl-bonded columns were tested. The effect of an ion-pair reagent (n-heptyl sulphonate) and pH of the mobile phase on the separation was examined. With the method described the concentrations of the four indoles can be determined within 45 min without sample pretreatment. The sensitivity obtained with electrochemical detection is 0.45 mumol/l for tryptophan and 2-4 nmol/l for 5-hydroxyindoles in human cerebrospinal fluid samples.

5-Hydroxytryptophan↗

PubMed1996

P-glycoprotein expression in canine lymphoma: a relevant, intermediate model of multidrug resistance.

BACKGROUND: Despite extensive investigation, the role of MDR of human cancer remains unclear. Canine lymphoma is a spontaneously arising correlate of human non-Hodgkin's lymphoma that may complement other in vivo models for investigation of issues related to MDR. METHODS: Immunoreactivity of primary antibodies to the human MDR1 gene product, p-glycoprotein 170 (Pgp), were determined in both a retrospective (n=76) and prospective (n=15) survey of canine lymphoma. Known prognostic factors and response to chemotherapy were correlated with categorical designations of Pgp expression. RESULTS: When combined, 61 of 91 samples (67%) were negative for Pgp, 16 of 91 (17.5%) had strong Pgp immunoreactivity in >50% of the malignant population and 14 of 91 (15.5%) had Pgp reactivity in 10-50% of cells. Pgp expression was greater after relapse compared with pretreatment samples [C494 83% vs. 25%; P=0.012 and C219 73% vs. 27%; P=0.04]. Pretreatment Pgp expression was an independent negative predictor of overall survival (median=225d vs. 367d; P=0.02). CONCLUSIONS: Pgp expression in spontaneous canine lymphoma is similar to that reported in human non-Hodgkin's lymphoma. Use of this model may expedite investigation of novel strategies for MDR prevention or modulation.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1984

An automated method to measure monoamines and metabolites using elevated temperature reversed phase HPLC with electrochemical detection. Application to striatal dopamine and hippocampal serotonin turnover.

High pressure liquid chromatography with electrochemical detection has been successfully used for the analysis of noradrenaline, dopamine(DA), serotonin(5-HT), and selected metabolites in brain. Automated sample injection allows up to 100 samples per day to be analyzed; precise thermostatic control of the chromatography at 45 degrees C increases both method reproducibility and separation efficiency while increasing column life. The method requires minimal sample pretreatment and is rapid and inexpensive. It has been applied to the analysis of rat and mouse whole brain and, in particular, to milligram samples of rat striatum and hippocampus, thus permitting the measurement of regional DA and 5-HT turnover. Effects of selected psychotropic drugs on these processes illustrate the value of the method to either DA or 5-HT turnover studies.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1991

Determination of clenbuterol in urine of calves by high-performance liquid chromatography with in series ultraviolet and electrochemical detection.

A method for the determination of clenbuterol in calf urine is described. After a simple two-step sample pretreatment, involving an Extrelut-3 column and a solid-phase extraction column (C2), the separation of clenbuterol from interfering compounds present in urine samples was performed with ion-pair chromatography on a LiChrospher RP-Select-B column with a mixture of acetonitrile and sodium dodecyl sulphate/acetate buffer (pH 3.5) as mobile phase. To obtain a higher specificity, two different physico-chemical detection techniques, i.e. UV-absorption (244 nm) and electrochemical detection (+1250 mV), were applied in series. The lowest limit of determination was 0.5 ng ml-1 and the mean recovery of clenbuterol spiked at 10 ng ml-1 level was 79.9% (RSD = 6.3%; n = 9). The analysis of one urine sample, including sample preparation, took less than 2 h. Results obtained with this method correlated well with GC-MS analysis. With the described method about 400 urine samples were analysed. In a pilot experiment, in which a calf received orally 4 micrograms clenbuterol.HCl per kilogram body weight twice a day (five times the therapeutic dose for oral application) for 5 days, the highest concentration of clenbuterol found in urine was 73 ng ml-1. In a second experiment, in which two calves received the therapeutic dose of clenbuterol.HCl twice a day over a period of 2 weeks, the highest concentration of clenbuterol was 75 ng ml-1 of urine. Eight days after the final application, concentrations of clenbuterol were lower than 0.5 ng ml-1. From this excretion study for clenbuterol a half-life value of approximately 1.5 days was calculated.

Administration, Oral↗

PubMed2005

Detection of Aspergillus fumigatus hyphae in respiratory secretions by membrane filtration, fluorescent labelling and laser scanning.

The detection of Aspergillus fumigatus hyphae in bronchoalveolar lavage fluid (BAL) and sputum is diagnostically useful in patients at risk of invasive aspergillosis. We report a dedicated enzymatic-chemical sample pretreatment that allows the application of a previously described solid phase cytometry (SPC) method for detection of A. fumigatus hyphae in sputum and BAL samples. Non-specific detection of fungal hyphae by SPC is based on a 'viability' staining using carboxyfluorescein diacetate. For a specific detection of A. fumigatus hyphae by SPC, viability staining is combined with a pre-incubation at 45 degrees C, immunofluorescent labelling and microscopic recognition of the characteristic hyphal morphology. Low numbers of A. fumigatus hyphae (2-10 hyphae/sample) have now been demonstrated in spiked sputum using the non-specific and specific staining in 2.5 and 8.5 h, respectively.

Aspergillosis↗

PubMed1998

Preconcentration and separation of antisense oligonucleotides by on-column isotachophoresis and capillary electrophoresis in polymer-filled capillaries.

Small, single-stranded, chemically modified oligonucleotides, complementary to a specific gene section, commonly referred to as antisense compounds, are being investigated as potential therapeutic drugs. A number of modified oligonucleotides, in particular phosphorothioates, are in clinical development. Shorter fragments are found as metabolic products. Isotachophoresis (ITP) allows the introduction of large, diluted sample plugs into the separation capillary. In this work, ITP and capillary electrophoresis (CE) in polymer solutions were successfully coupled in a single capillary in a commercial instrument to increase sensitivity with UV detection and to shorten the time for sample pretreatment. It was shown that ITP-CE can be used as a preconcentration and clean-up method for phosphodiester- and phosphorothioate-containing samples. Up to 3 microL sample could be injected into the capillary without significantly disturbing the separation performance. ITP-CE of phosphodiesters directly out of salt- and protein-containing samples could be demonstrated. For phosphorothioates in serum samples an additional sample clean-up was necessary, due to oligonucleotide-protein binding. An optimized replaceable polymer solution was developed to increase the separation performance for heterogeneous phosphorothioates. A dextran-based sieving medium showed a good separation performance in ITP-CE of phosphorothioates. A concentration detection limit of 8.10(-9) mol/L for the 20-mer phosphorothioate ISIS5132, isolated from rat serum, was found.

Animals↗

PubMed1990

Determination of trace selenium in human body by anodic stripping voltammetry at gold-disc electrode.

For determination of trace Se we used high-pressure wet digester to pretreat the specimens obtained from the human body. This method is very effective in preventing loss of Se by volatilization which often occurs in the sample pretreatment. We studied the method of using anodic stripping voltammetry at gold-disc electrode to measure the trace Se present in the human body and found it to be the optimal procedure. The detection limitation was about 2 x 10(-8) g/L, the recovery rate of Se about 96.6 +/- 6.7% (chi +/- s), and the coefficient of variation CV = 7.0%.

Amniotic Fluid↗

PubMed2006

Highly selective micro-sequential injection lab-on-valve (muSI-LOV) method for the determination of ultra-trace concentrations of nickel in saline matrices using detection by electrothermal atomic absorption spectrometry.

A highly selective procedure is proposed for the determination of ultra-trace level concentrations of nickel in saline aqueous matrices exploiting a micro-sequential injection Lab-On-Valve (muSI-LOV) sample pretreatment protocol comprising bead injection separation/pre-concentration and detection by electrothermal atomic absorption spectrometry (ETAAS). Based on the dimethylglyoxime (DMG) reaction used for nickel analysis, the sample, as contained in a pH 9.0 buffer, is, after on-line merging with the chelating reagent, transported to a reaction coil attached to one of the external ports of the LOV to assure sufficient reaction time for the formation of Ni(DMG)(2) chelate. The non-ionic coordination compound is then collected in a renewable micro-column packed with a reversed-phase copolymeric sorbent [namely, poly(divinylbenzene-co-N-vinylpyrrolidone)] containing a balanced ratio of hydrophilic and lipophilic monomers. Following elution by a 50-muL methanol plug in an air-segmented modality, the nickel is finally quantified by ETAAS. Under the optimized conditions and for a sample volume of 1.8 mL, a retention efficiency of 70 % and an enrichment factor of 25 were obtained. The proposed methodology showed a high tolerance to the commonly encountered alkaline earth matrix elements in environmental waters, that is, calcium and magnesium, and was successfully applied for the determination of nickel in an NIST standard reference material (NIST 1640-Trace elements in natural water), household tap water of high hardness and local seawater. Satisfying recoveries were achieved for all spiked environmental water samples with maximum deviations of 6 %. The experimental results for the standard reference material were not statistically different to the certified value at a significance level of 0.05.

Journal Article↗

PubMed1995

Analysis of basic antimalarial drugs by CZE; Part 2. Validation and application to bioanalysis.

This report describes some of the quantitative aspects of the CZE separation of proguanil, chloroquine and their respective metabolites, the separations of which, by CE and MEKC, were reported in Part 1. Results obtained on the precision of migration time and peak areas using the alternative injection methods of vacuum and electrokinetic are described and discussed. The increase in concentration sensitivity using electrokinetic injection with an organic injection solvent reported in Part 1 is confirmed and the resultant limits of detection in urine reported. An assay method for these compounds in urine is described which incorporates a pretreatment stage of solid phase extraction and the main analytical parameters used in the validation of such an assay are reported. The limitation of the sample pretreatment used when applied to matrices of plasma and saliva are reported and discussed in the context of the electrokinetic injection method used.

Antimalarials↗

PubMed2000

Determination of fumaric acid in apple juice by on-line coupled capillary isotachophoresis-capillary zone electrophoresis with UV detection.

An on-line coupled capillary isotachophoresis-capillary zone electrophoresis (cITP-CZE) method for the determination of the fumaric acid content in apple juice is presented. A clear separation of fumaric acid in real samples is achieved within 20 min. The leading, terminating and background electrolyte of the employed system consist of 10 mM HCl+beta-alanine+5 mM beta-cyclodextrin+0.05% hydroxypropylmethylcelullose (HPMC), pH 3, 10 mM citric acid and 20 mM citric acid+beta-alanine+5 mM beta-cyclodextrin+0.1% HPMC, pH 3.3, respectively. The linearity, recovery, repeatability and detection limit of the developed method are 25-1000 ng/ml, 1.07%, 95.4+/-3.5 (+/-s)% and 10 ng/ml, respectively. Low laboriousness (no sample pretreatment), sufficient sensitivity and low running cost are the important attributes of the cITP-CZE method which was successfully applied to analyses of real samples of apple juices.

Beverages↗

PubMed2002

Determination of acetyl gestagenic steroids in kidney fat by automated supercritical fluid extraction and liquid chromatography ion-trap mass spectrometry.

Acetyl gestagenic steroids are isolated from animal tissues such as bovine kidney fat by automated supercritical fluid extraction (SFE). After the addition of internal standards and sample pretreatment, the analytes are extracted from the matrix by supercritical CO2 and trapped directly in-line on alumina placed in the extraction vessel. The samples are analysed by liquid chromatography combined with ion-trap mass selective detection (LC-MSn). For quantification, deuterated internal standards are added and single ions of the analytes and internal standards are monitored. For confirmation of the identity of the analytes, two transition ions (one MS2 and one MS3) were monitored and the ratios between the ions were calculated and compared with those of standards. The detection capability for the multi-analyte LC-MSn analysis of megestrol acetate (MA), medroxyprogesterone acetate (MPA), chlormadinone acetate (CMA) and melengestrol acetate (MGA) is 0.5 microg kg(-1). The mean within-laboratory reproducibility ranges from 16-19% (%RSD) at a concentration level of 0.5 microg kg(-1) (n = 9). Running the SFE procedure overnight allows the analysis of 24 samples of fat per day.

Animals↗

PubMed1998

Evolution of an inhibin A ELISA method: implications for Down's syndrome screening.

The development of a sensitive and specific enzyme-linked immunoassay (ELISA) for inhibin A stimulated the observation that inhibin A was a useful prenatal marker of Down's syndrome. Modifications of that ELISA, in terms of preassay sample treatment, detection methods and standard preparation, were subsequently introduced to improve assay performance and reduce costs. These modified formats have been validated and reported. We describe the modifications in detail, explaining the rationale for each, and report the results of a study directly comparing the various ELISA formats in terms of assay performance when applied to clinical samples and ability to differentiate between normal and Down's syndrome pregnancies. A format involving sample pretreatment with sodium dodecylsulphate at 100 degrees C was found to give better assay performance and a modest improvement in discrimination between Down's syndrome samples and controls, and we recommend this format for use by other investigators.

Down Syndrome↗

PubMed1997

Expression of epidermal growth factor receptor and c-erbB2 during the development of tamoxifen resistance in human breast cancer.

Expression of epidermal growth factor receptor (EGFR) or of c-erbB2 in primary breast cancer has been shown to predict for a poor chance of subsequent response of recurrent/metastatic disease to endocrine therapy. To assess the role of these receptors in the development of tamoxifen resistance, we examined their expression immunohistochemically on paraffin-embedded sections from breast cancers from 155 patients whose disease was progressing on tamoxifen therapy. Patients were categorized into those who initially responded to therapy (n = 56), those who never responded (n = 39), and those who relapsed while on adjuvant therapy and may or may not have "responded" (n = 60). In 61 cases, pretreatment specimens were also obtained for direct comparison with the resistance specimen for each patient. None of the 18 pretreatment samples from patients who responded to therapy expressed c-erbB2, and 1 of 18 expressed EGFR. Of the nonresponders, 7 of 18 expressed EGFR pretreatment, and 4 of 18 expressed c-erbB2 (1 patient expressed both receptors). Results confirmed previous findings that when considered independently, expression of either receptor pretreatment tended to predict for a poor chance of response (EGFR, P = 0.046; c-erbB2, P = 0.11). Importantly, patients who were either EGFR positive and/or c-erbB2 positive had a much poorer chance of response than "double negatives" (response rates of 1 of 11 and 17 of 25, respectively; P = 0.0039). At the time of disease progression compared to pretreatment, there was no significant change in expression of either receptor, irrespective of initial response. The inverse relationship between EGFR and estrogen receptor was maintained at relapse on tamoxifen. These data argue strongly against the acquired expression of these receptors during treatment playing a major role in the development of tamoxifen resistance in human breast cancer.

Adult↗