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At least 649 records · Page 36Linked to original sources
PubMed2004

Separation of stereoisomers of some terpene derivatives by capillary gas chromatography-mass spectrometry and high-performance liquid chromatography using beta-cyclodextrin derivative columns.

Gas chromatographic separations of the stereoisomers of menthol derivatives, important intermediates in the synthesis of physiologically active natural products, were carried out on several substituted beta-cyclodextrin (CD) columns, including per-O-methyl-beta-cyclodextrin (PME-beta-CD), heptakis(2,3-di-O-acetyl-6-tert-butyldimethylsilyl)-beta-CD (DIAC-6-TBDS-beta-CD), and heptakis(2,3-di-O-methyl-6-tert-butyldimethylsilyl)-beta-CD (DIME-6-TBDS-beta-CD) as chiral stationary phases (CSPs). With the DIME-6-TBDS-beta-CD column, a separation of the Z- and E-isomers of methylidenementhol was accomplished; no separation was achieved with the other columns. The stereoisomers of methylidenementhol and the corresponding tert-butyldimethylsilyl (TBS) ether were separated on both the beta-CD and the heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TME-beta-CD) columns by high-performance liquid chromatography (HPLC) with a mobile phase involving acetonitrile and H(2)O. For the separation of the Z- and E-isomers of methylidenementhol, the TME-beta-CD column was superior. In contrast, the beta-CD column was preferable in the case of the corresponding TBS ether.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Lipids in blood-brain barrier models in vitro I: Thin-layer chromatography and high-performance liquid chromatography for the analysis of lipid classes and long-chain polyunsaturated fatty acids.

The objectives of this study were to optimize a sensitive high-performance liquid chromatography (HPLC) method for fatty acid (FA) analysis for the quantification of polyunsaturated FAs (PUFAs) in cell lipid extracts and to analyze the lipid and FA patterns of three cell lines used in blood-brain barrier (BBB) models: RBE4, ECV304, and C6. Thin-layer chromatographic analysis revealed differences in the phosphatidylcholine-phosphatidylethanolamine (PC:PE) ratios and the triglyceride (TG) content. The PC:PE ratio was <1 for RBE4 cells but >1 for ECV304 and C6 cells. ECV304 cells displayed up to 9% TG depending on culture time, whereas the other cell lines contained about 1% TG. The percentages of docosahexaenoic acid were 9.4 +/- 1.7% of the unsaturated FAs in RBE4 cells (n = 5; 4 d in culture; 9.9% after 10 d), 8.1 +/- 2.0% in ECV304 cells (n = 11; 10 to 14 d), and 6.7 +/- 0.6% in C6 cells (n = 6; 10 to 14 d) and were close to the published values for rat brain microvascular endothelium. The percentage of arachidonic acid (C20:4) was about half that in vivo. ECV304 cells contained the highest fraction of C20:4, 17.8 +/- 2.2%; RBE4 cells contained 11.6 +/- 2.4%; and C6 cells 15.8 +/- 1.9%. It is concluded that a sensitive HPLC method for FAs is now optimized for the analysis of long-chain PUFAs. The results provide a useful framework for studies on the effects of lipid modulation and give reference information for the development of further BBB models.

Animals↗
PubMed2004

The determination and quantification of photosynthetic pigments by reverse phase high-performance liquid chromatography, thin-layer chromatography, and spectrophotometry.

Chorophylls and carotenoids are functionally important pigment molecules in photosynthetic organisms. Methods for the determination of chlorophylls a and b, beta-carotene, neoxanthin, and the pigments that are involved in photoprotective cycles such as the xanthophylls are discussed. These cycles involve the reversible de-epoxidation of violaxanthin into antheraxanthin and zeaxanthin, as well as the reversible de-epoxidation of lutein-5,6-epoxide into lutein. This chapter describes pigment extraction procedures from higher plants and green algae. Methods for the determination and quantification using high-performance liquid chromatograpy (HPLC) are described as well as methods for the separation and purification of pigments for use as standards using thin-layer chromatography (TLC). In addition, several spectrophotometric methods for the quantification of chlorophylls a and b are described.

Arabidopsis↗
PubMed1997

The optimized use of gas chromatography-mass spectrometry and high performance liquid chromatography to analyse the serum bile acids of patients with metabolic cholestasis and peroxisomal disorders.

We have measured the bile acids in human serum as methyl ester-trimethylsilyl ethers by gas chromatography-mass spectrometry (GC-MS) using an electron ionization procedure. The overall method was validated and the detection limit (0.4 mumol/l), linearity (2-30 mumol/l), intra-day and inter-day precision, accuracy and recovery (96.2% for nor-23-deoxycholic acid as internal standard) were measured. Serum C24-bile acids profiles from 43 cholestatic patients were measured by GC-MS and by HPLC. The results obtained with the two methods were well correlated and the criteria for selecting either HPLC or GC-MS identified. The serum C24- and C27-bile acids and C29 dicarboxylic bile acid profiles for patients with generalized peroxisomal deficiencies, like Zellweger syndrome (n = 5), neonatal adrenoleukodystrophy (n = 1), infantile Refsum disease (n = 2) and from a single peroxisomal deficiency (n = 1) were also measured by GC-MS.

Adrenoleukodystrophy↗
PubMed2026

Exploring the potential mechanism of Huang'e capsule against spontaneous benign prostatic hyperplasia in beagle dogs using high-performance liquid chromatography-quadrupole-time-of-flight tandem mass spectrometry, gas chromatography-mass spectrometry, and network pharmacology.

OBJECTIVE: To investigate the therapeutic efficacy and potential mechanisms of Huang'e capsule (, HEC) against benign prostatic hyperplasia (BPH). METHODS: The chemical profile of HEC was characterized using high-performance liquid chromatographyquadrupole-time-of-flight tandem mass spectrometry (HPLC-Q-TOF-MS/MS) and gas chromatography-mass spectrometry (GC-MS) techniques. Network pharmacology was employed to analyze potential active compounds, core targets, and key signaling pathways. A spontaneous canine BPH model was used to evaluate the efficacy of HEC and to validate the predictions from network pharmacology. RESULTS: A total of 51 chemical components of HEC were identified, comprising 19 from HPLC-Q-TOF-MS/MS and 32 from GC-MS analyses. The "components-targets-pathways-disease" network analysis predicted active compounds including (s)-coriolic acid, ethyl linoleate, peroxysimulenoline, physcion, and kaempferol. Core targets identified included cytochrome P450 family 19 subfamily A member 1, estrogen receptor 2 (ESR2), ESR1, and androgen receptor (AR). Kyoto Encyclopedia of Genes and Genomes enrichment analysis suggested that HEC's effects on BPH involve pathways related to cancer, phosphatidylinositol 3-kinase (PI3K) -protein kinase B (Akt)-signaling, proteoglycans in cancer, and prostate cancer signaling. Animal experiments showed that HEC significantly improved maximum urinary flow rates, reduced prostate weight, volume, and prostate index, and ameliorated histopathological changes. HEC regulated the balance between apoptosis and proliferation by downregulating AR and estrogen receptor alpha expression, while upregulating estrogen receptor beta expression. CONCLUSION: These findings indicate that HEC effectively ameliorates spontaneous BPH in beagle dogs, likely by regulating the balance between cell apoptosis and proliferation through multiple signaling pathways.

Animals↗
PubMed2001

[Determination of sucralose in foods by anion-exchange chromatography and reverse-phase chromatography].

Simple and rapid methods for the determination of sucralose in foods were developed using anion-exchange chromatography (AEC) with pulsed amperometric detection and reverse-phase HPLC with refractive index detection. Sucralose was extracted with water or methanol, and the extracted solution was cleaned up on a Sep-Pak C18 cartridge and a Sep-Pak Alumina N cartridge. The AEC separation was performed on a CarboPac PA1 column (4.0 mm i.d x 250 mm) using 100 mmol/L sodium hydroxide-50 mmol/L sodium acetate solution as the mobile phase at a flow rate of 1.0 mL/min. The recoveries of sucralose from foods were 80.6-102.0%, and quantitation limits from foods except chewing gum were 0.5 microgram/g (2 micrograms/g from chewing gum). The reverse-phase HPLC separation was performed on an Inertsil ODS-3V column (4.6 mm i.d x 150 mm) using methanol-water (25:75) as the mobile phase at a flow rate of 1.0 mL/min. The recoveries of sucralose from foods were 80.2-121.2%, and quantitation limits from foods except chewing gum were 5 micrograms/g (20 micrograms/g from chewing gum).

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Assay of tinidazole in human serum by high-performance thin-layer chromatography--comparison with high-performance liquid chromatography.

Determination of tinidazole in human serum by high-performance thin-layer chromatography (HPTLC) is presented. It includes use of 10 x 10 cm plates coated with silica gel 60 and chloroform-acetonitrile-acetic acid (60 + 40 + 2) as mobile phase. Quantitation was performed by densitometry at 320 nm. The linearity (1-10 ng), precision (6%), reproducibility (5%), recovery (96%), and detection limit (1 mg/L) of tinidazole determination by HPTLC were comparable with corresponding method parameters by reversed-phase HPLC. A satisfactory correlation was found between the 2 analytical methods. The procedure was used to quantitate tinidazole in patient sera.

Antitrichomonal Agents↗
PubMedDate not supplied

Multiresidue determination of 19 fungicides in processed fruits and vegetables by capillary gas chromatography after gel permeation chromatography.

A gas chromatographic (GC) method was developed for simultaneous determination of 19 fungicides (chlorothalonil, vinclozolin, dichlofuanid, triadimefon, penconazole, chlozolinate, captan, procymidone, triadimenol, folpet, hexaconazole, myclobutanil, cyproconazole, propiconazole, nuarimol, captafol, iprodione, fenarimol, and bitertanol) and the acaricide tetradifon in tomato puree, peach nectar, orange juice, and canned peas. Samples were extracted with acetone, partitioned with ethyl acetate-cyclohexane (50 + 50, v/v), and cleaned using gel permeation chromatography with ethyl acetate-cyclohexane (50 + 50, v/v) as eluant. The final extract was analyzed by GC with ion trap mass spectrometry (ITMS) using a DB5 capillary column. Recoveries from fortified samples ranged from 74.6 to 99.3%, except for triadimenol and bitertanol. Quantitation limits for most analytes were between 0.005 and 0.050 mg/kg. The purified extracts were analyzed further by GC with electron capture and nitrogen phosphorus detection, and the results were compared with those obtained by ITMS.

Chromatography, Gas↗
PubMed2000

Evaluation of ursodeoxycholic acid bioavailability from immediate- and sustained-release preparations using gas chromatography-mass spectrometry and high-performance liquid chromatography.

An improved procedure is presented for the determination of ursodeoxycholic acid (CAS 128-13-2, UDCA) in human plasma and bile after oral administration of UDCA-containing dosage forms. The plasma samples after solid-phase extraction with silica-based C18- and strong anion exchange cartridges were assayed by gas chromatography-mass spectrometry (GC-MS) using selected-ion monitoring. The hexafluoroisopropyl trifluoroacetate ester derivative of UDCA was selected for GC analysis since it is easily and rapidly prepared by a one-step reaction. Biliary UDCA levels were determined by a rapid and simple high-performance liquid chromatographic (HPLC) method with on-line sample purification. This analytical protocol was used to investigate the pharmacokinetic of a new sustained-release capsule of UDCA in comparison with a reference immediate-release preparation after single oral administration. Statistical evaluation of the area under the plasma concentration-time curves indicated that two formulations are equivalent with regard to the amount of drug absorbed. However, pharmacokinetic data showed that with the sustained-release preparation a significantly delayed mean peak plasma level was reached compared with the reference preparation. Moreover, the immediate- and extended-release capsules were found to achieve a comparable degree of biliary enrichment with UDCA.

Adult↗
PubMedDate not supplied

Determination of paraffins in food simulants and packaging materials by liquid chromatography with evaporative mass detection and identification of paraffin type by liquid chromatography/gas chromatography and fourier transform infrared spectroscopy.

A liquid chromatographic method with evaporative mass detection (EMD) is described for the determination of paraffins in food contact materials that do not contain polyolefin oligomers, or paraffins migrating from these materials into fatty food simulants or certain simple foods. A normal-phase column operating at maximum column efficiency separates nonparaffinic and paraffinic materials without resolving the latter into individual components, and EMD is used to quantitate the paraffins. An on-line qualitative method that uses liquid chromatography/gas chromatography with flame ionization detection discriminates between paraffin waxes and oils in food contact materials, food simulants, and certain simple foods; a Fourier transform infrared spectrophotometric qualitative method also discriminates between waxes and oils, but is usually restricted to food contact materials that do not contain polyolefins and to migration experiments with organic solvents as fatty food simulants (with some other fatty food simulants, paraffin type must then be identified in the food contact material).

Chromatography, Gas↗
PubMedDate not supplied

Determination of chloramphenicol residue in chicken tissues by immunoaffinity chromatography cleanup and gas chromatography with a microcell electron capture detector.

A rapid and sensitive gas chromatography (GC) method was developed to detect chloramphenicol in chicken tissues. The extracted samples were cleaned up using the immunoaffinity column prepared by coupling antichloramphenicol monoclonal antibody with cyanogen bromide-activated Sepharose 4B. The dynamic column capacity of chloramphenicol was 3265 ng/mL gel. The eluate was evaporated to dryness, and residues were derivatized and determined by GC with a microcell electron capture detector. Average recoveries were 86.6 to 96.9% for chicken muscle and 74.3 to 96.1% for chicken liver. The limit of quantitation of the method was 0.05 ng/g for chicken muscle and 0.1 ng/g for chicken liver.

Animals↗
PubMedDate not supplied

Determination of residues of 446 pesticides in fruits and vegetables by three-cartridge solid-phase extraction-gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry.

A method was developed for determination of residues of 446 pesticides in fruits and vegetables through the use of cleanup by a 3-cartridge solid-phase extraction-gas chromatography/ mass spectrometry (GC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS). Fruit and vegetable samples (20 g) were extracted with 40 mL acetonitrile, salted out, and centrifuged. Half of the supernatant was passed into an Envi-18 cartridge, eluted with acetonitrile, and cleaned up with Envi-Carb and aminopropyl Sep-Pak cartridges in series after concentration of the eluates. Pesticides were eluted with acetonitrile-toluene (3 + 1, v/v), and eluates were concentrated to 0.5 mL and then added into internal standards after solvent exchange with 2 mL hexane and used for determination of 383 pesticides by GC/MS. The other half of the supernatant was concentrated to 1 mL and cleaned up with Envi-Carb and aminopropyl Sep-Pak cartridges in series. Pesticides were eluted with acetonitrile-toluene (3 + 1, v/v), and the eluates were concentrated to 0.5 mL, dried with nitrogen gas, diluted to 1.0 mL with acetonitrile-water (3 + 2, v/v), and used for determination of 63 pesticides by LC/MS/MS. The limit of detection for the method was 0.2-600 ng/g depending on the individual pesticide. In the method, fortification recovery tests at high, medium, and low levels were conducted on 6 varieties of fruits and vegetables, i.e., apples, oranges, grapes, cabbage, tomatoes, and celery, with average recoveries falling within the range of 55.0-133.8% for 446 pesticides, among which average recoveries between 60.0-120.0% accounted for 99% of the results. The relative standard deviation was between 2.1-39.1%, of which a relative standard deviation of 2.1-25.0% made up 96% of the results. Experiments proved that the method was applicable for determination of residues of 446 pesticides in fruit and vegetables.

Acetonitriles↗
PubMed1982

Application of gel permeation chromatography and nonaqueous reverse phase chromatography to high performance liquid chromatographic determination of retinyl palmitate and alpha-tocopheryl acetate in infant formulas.

A high performance liquid chromatographic (HPLC) method was developed for determining retinyl palmitate and alpha-tocopheryl acetate in infant formulas. The lipid-soluble components were extracted from the aqueous phase by homogenizing in a solvent mixture of isopropanol and methylene chloride with magnesium sulfate added to remove water. The vitamins were fractionated from the lipid material by using high pressure gel permeation chromatography (HP-GPC) followed by quantitation using non-aqueous reverse phase (RP)-HPLC. Three muStyragel (100A) columns connected in series were used for HP-GPC fractionation of sample extracts in methylene chloride. A Zorbax ODS (6 micron) column and methylene chloride-acetonitrile-methanol (30 + 70 + 0.2) were used for RP-HPLC quantitation. The 32 commercial infant formulas that were analyzed represent a wide variety of formulations manufactured at various fortification levels. Vitamin A results ranged from 89 to 242% of the declared levels. Vitamin E values, determined as the supplemental form alpha-tocopheryl acetate, ranged from 83 to 272% of the declared levels. Determination of vitamin A in 6 samples and vitamin E in one sample by this method and the official AOAC method gave comparable results. This method, which requires no saponification, was successfully used to determine vitamins A and E in ready-to-use, liquid concentrated, and powdered infant formulas.

Chromatography, Gel↗
PubMed1981

Evaluation of high pressure liquid chromatography and gas-liquid chromatography for quantitative determination of sugars in foods.

A method has been developed for separation and determination of 5 sugars in foods. Mixtures of sugars were separated by high pressure liquid chromatography (HPLC) with a muBondapak/carbohydrate column and acetonitrile-water (80 + 20) as the mobile phase. For the gas-liquid chromatographic (GLC) determination, the sugars were reacted with hydroxylamine hydrochloride to give the oximes, which were then converted to trimethylsilyl derivatives. The derivatives were separated on an 8 ft column containing 3% JXR as the liquid phase. The GLC preparative time was considerably longer than that for HPLC. Both methods were applied to the determination of fructose, glucose, sucrose, maltose, and lactose in processed foods. Recovery studies showed better accuracy for the HPLC method. Because of incomplete derivatization and/or the formation of anomers, the GLC method was not applicable to all foods.

Carbohydrates↗
PubMed1980

Application of gel permeation chromatography and nonaqueous reverse phase chromatography to high pressure liquid chromatographic determination of retinyl palmitate in fortified breakfast cereals.

A high pressure liquid chromatographic (HPLC) method was developed for determing retinyl palmitate in cereals. Retinyl palmitate is fractionated from other methylene chloride-soluble components by using high pressure gel permeation chromatography (HP-GPC) followed by quantitation with nonaqueous reverse phase (HPLC (RP-HPLC). HP-GPC fractionation was accomplished using 2 microStyragel (100A) columns connected in series on sample extracts in methylene chloride with methylene chloride as the mobile phase. A valve designed to facilitate the collection of the vitamin A fraction was installed in-line between the refractive index and absorbance detectors. RP-HPLC quantitation was achieved on microBondapak C18 (10 micrometers) using methylene chloride-acetonitrile (30 + 70). Based on 23 repetitive analyses, recovery of vitamin A as retinyl palmitate in cereal products was 95.4 +/- 4.2% with spiking levels between 21.4 and 140 micrograms/g. Vitamin A in 15 cereals, representing bran, corn, oats, rice, and wheat, ranged from 34 to 194% of the declared level. The HPLC procedure was compared with the AOAC official colorimetric method and with an ultraviolet spectrophotometric method.

Chromatography, Gel↗
PubMed1998

High performance liquid chromatography mobile phase composition optimization for the quantitative determination of a carboxylic acid compound in human plasma by negative ion electrospray high performance liquid chromatography tandem mass spectrometry.

A systematic investigation was undertaken to study the effects of varying concentrations of additives in the acetonitrile/water high performance liquid chromatography mobile phase, especially formic acid and ammonium formate, on the negative ion electrospray response of a carboxylic acid compound. The study showed that the response progressively decreased with increase in the formic acid concentration. While such a decrease in the response could be qualitatively explained by the decrease in the concentration of the ionized form of the carboxylic acid compound due to the lower pH of the mobile phase, the change in response was not as large as expected from the change of the concentration of the ionized form. The response also progressively decreased with increase in the ammonium formate concentration but the decrease cannot be explained by the change in the pH of the mobile phase. Although the best negative ion electrospray response was obtained with a water/acetonitrile mobile phase that contained no additives at all, the retention time of the analyte was not found to be adequately reproducible on repeated injections. Thus, this mobile phase was deemed unacceptable for practical, routine use. Comparing formic acid against ammonium formate, the former was preferable since it caused a smaller attenuation of the negative ion response. Equally important was the fact that addition of formic acid had the desirable effect of maintaining a reasonably high capacity factor (k') for the analyte even at a relatively high acetonitrile concentration. A concentration of 1 mM formic acid in the mobile phase was large enough to achieve the reproducible elongated retention time for the analyte, with a loss in the analyte response of about 60% only. It should be noted that the sensitivity achieved with the 1 mM formic acid mobile phase, in which the carboxylic acid is expected to be about 10% in the ionized form, is about 9 times better than the sensitivity achieved in the 1 mM ammonium formate mobile phase, in which the carboxylic acid is expected to be about 99% in the ionized form.

Carboxylic Acids↗
PubMed2005

Comparison of microemulsion electrokinetic chromatography and micellar electrokinetic chromatography as methods for the analysis of ten benzophenones.

Microemulsion electrokinetic chromatography (MEEKC) and micellar electrokinetic chromatograpy (MEKC) were compared for their abilities to separate and detect ten similar benzophenones, which are commonly used as UV filters in various plastic and cosmetic products. Sodium dodecyl sulfate (SDS) concentration and column temperature rarely affected separation resolution for MEEKC, but separation of benzophenones could be improved by changing the SDS concentration and column temperature for MEKC. Buffer pH and ethanol (organic modifier) were found to markedly influence the separation selectivity for both MEEKC and MEKC systems. In addition, a higher electric voltage improved the separation efficiency without a noticeable reduction in separation resolution for MEEKC, whereas it caused a poor separation resolution for the MEKC system.

Benzophenones↗
PubMed1978

Liquid chromatography in pharmaceutical analysis IX: Determination of muscle relaxant--analgesic mixtures using normal phase chromatography.

High-pressure liquid chromatography was used to optimize the resolution of eight widely prescribed therapeutic agents commonly found in muscle relaxant--analgesic mixtures. The compounds were chromatographed on normal phase porpous silica or cyanopropylsilane columns, using various solvent systems paired on the basis of Synder's solvent selectivity scheme to give a polarity index for each system of 3.3. A carisoprodol, phenacetin, and caffeine mixture was selected to demonstrate the utility of the separation and quantification method. The mixture was chromatographed on a porous silica column, using tetrahydrofuran--toluene (50:50) at a flow rate of 2.0 ml/min. Each determination can be achieved in approximately 8 min with an accuracy of 3--5%.

Analgesics↗