Simple gas chromatographic method for furfural analysis

A new, simple, gas chromatographic method was developed for the direct analysis of 5-hydroxymethylfurfural (5-HMF), 2-furfural (2-F) and 5-methylfurfural (5-MF) in liquid and water soluble foods, using direct immersion SPME coupled to GC-FID and/or GC-TOF-MS. The fiber (DVB/CAR/PDMS) conditions were optimized: pH effect, temperature, adsorption and desorption times. The method is simple and accurate (RSD<8%), showed good recoveries (77-107%) and good limits of detection (GC-FID: 1.37 microgL(-1) for 2-F, 8.96 microgL(-1) for 5-MF, 6.52 microgL(-1) for 5-HMF; GC-TOF-MS: 0.3, 1.2 and 0.9 ngmL(-1) for 2-F, 5-MF and 5-HMF, respectively). It was applied to different commercial food matrices: honey, white, demerara, brown and yellow table sugars, and white and red balsamic vinegars. This one-step, sensitive and direct method for the analysis of furfurals will contribute to characterise and quantify their presence in the human diet.     

Development of gas chromatographic method for determination of cholesterol oxides in meat products

Summary A method of extraction, purification and gas chromatographic analysis of five cholesterol oxidation products (COPs) (7β-hydroxycholesterol, 5α, 6α-epoxycholesterol, 25-hydroxycholesterol, 7-ketocholesterol and cholestane-3β, 5α, 6β-triol) has been developed. The method is aimed at the determination of COPs in meat and meat products, in particular dry sausages, where large differences in the content of cholesterol and its oxidation derivatives may occur. Linearity of response of trimethylsilyl ethers was defined. The minimum concentration tested was 2.5 μg g⁻¹ in the injected solution. The main feature of the present work is the addition of a purification step of unsaponifiables by SPE on silica cartridges. Extraction recoveries of COP standard mixtures, performed with or without the SPE step, are evaluated. The introduction of the clean-up step results in high purity samples without further losses in the entire process.     

Micromethod for the gas chromatographic quantification of blood ethanol

A microadaptation for the head space analysis of ethanol in 20-μl blood samples is described. Ethanol concentration is determined by comparison of the derivatized ethanol peak area with that of a 1-propanol internal standard. Reaction of the alcohols with nitrous acid followed by a warming of the mixture greatly enhances peak sizes. The method is rapid, sensitive, and highly reproducible for the concentrations encountered during the linear phase of the ethanol elimination curve in laboratory rats.     

Simple gas chromatographic method for the determination of medicagenic acid in alfalfa (Medicago sativa)

A gas chromatographic method for the determination of medicagenic acid in alfalfa leaves, stems, entire plant (tops) and roots and also in leaf protein concentrates is described. The method is based on extraction of lucerne saponins followed by hydrolysis of the triterpene glycosides. After derivatization of the liberated sapogenins to silylated products, the trimethylsilylated medicagenic acid was determined by gas chromatography. The sensitivity of the method permits the detection of 50 ng of medicagenic acid.     

Simple gas chromatographic method for the stereodifferentiation of methyl nilate, a chiral alpha-methyl-beta-hydroxy ester

The four stereoisomers of methyl nilate, methyl 3-hydroxy-2-methylbutanoate, have been separated and analyzed by the direct simultaneous achiral-chiral high-resolution gas chromatography (HRGC) and also by the chiral high-resolution gas chromatography-time-of-flight mass spectrometry (HRGC-TOF-MS). The method involved the use of DB-5 and CP Chirasil-Dex CB columns. The elution sequences on the two columns were determined and are reported. The one-step GC method allows the identification by retention data and simultaneously to determine unequivocally the absolute configuration of nilic acid moieties contained in minor complex natural products without previous isolation, as part of a general strategy for the structure determination of the compounds.     

A chromatographic method for baicalin quantification in rat thalamus

A rapid reversed-phase high-performance liquid chromatographic (rp-HPLC) assay for the determination of baicalin in rat thalamus was developed. This was carried out on a Hypersil -C(18) column using 4-nitro-benzoic acid as the internal standard with a mobile phase of methanol-water-H(3)PO(4) (45:55:0.2, v/v/v). Detection was by UV at 277 nm. The calibration curve for baicalin was linear (r=0.9992) over the concentration range of 0.05--4.0 microg/mL and the limit of detection was 10 ng/mL. The coefficients of variation of intra- and inter-day assays were 2.64, 5.19 and 3.19% and 3.46, 6.21 and 5.58% at concentrations of 0.5, 1.0 and 3.0 microg/mL, respectively. The recoveries of baicalin from rat thalamus were 85.4+/- 5.62, 90.7+/- 2.43 and 89.1+/- 4.75% at concentrations of 0.5, 1.0 and 3.0 microg/mL, respectively. The method was applied to determine the time course of baicalin in rat thalamus, following a single dosage of intravenous administration of Scutellariae radix extract at 90 mg/kg of baicalin to male Wistar rats.     

An on-column capillary gas chromatographic method for the analysis of synthetic pyrethroid residues on fish eggs

A sensitive and reproducible residue method is described for the determination of cypermethrin and deltamethrin in fish eggs. The limit of determination of 0.0005 mg kg^?1 is achieved using only a very small sample size; typical sample weights lie in the range of 0.1-1 g of fathead minnow or trout eggs. The method involves tissue homogenization (tube homogenizer) followed by hot acetonitrile extraction, then sequential C₈, aluminum oxide, and silica gel clean-up. The clean-up is carried out in glass columns using cotton wool plugs in order to minimize potential sample contamination by plasticizers. Residues are determined by capillary chromatography using automated on-column injection with electron-capture detection. Confirmation of residues by gas chromatography-mass spectrometry using selected ion monitoring (SIM), is also described.     

Simple thin-layer chromatographic purification procedure for the determination of cholesterol ester fatty acid compositions

A mild procedure for the purification of methyl esters of the fatty acid components of cholesterol esters, from interfering free cholesterol and other contaminating residues, is described. Methyl esters and free cholesterol are formed during the methylation of cholesterol esters. When co-extracted, cholesterol and other contaminating residues interfere with the methyl esters because minute proportions of these residues tend to elute at the same retention times as palmitoleic and stearic acids, to yield unreliable but significantly higher values for palmitoleic (p less than 0.001) and stearic acids (p less than 0.0001), and correspondingly lower values for oleic acid (p less than 0.0001). Purification of methyl esters by thin-layer chromatography eliminates this problem and yields reliable analysis of cholesterol ester fatty acids, without measurable oxidation of unsaturated fatty acids.     

A gas chromatographic method for the microdetermination of iodine

Summary Iodine was quantitatively converted by reaction with acetone to a form which was easily separated by gas chromatography and which was easily detected with an electron capture detector. Linear response of the detector was obtained for solutions which contained up to 1g/ml with an uncertainty of 8%. Milligram amounts of chloride or bromide andg amounts of iodide do not interfere. Amplification of the amount of reaction product and the determination of both iodine and iodide was accomplished by the addition of KIO₃.

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Zusammenfassung Jod wird quantitativ mit Aceton umgesetzt und läßt sich dann gaschromatographisch abtrennen und mit einem Elektroneneinfangdetektor nachweisen. Dessen Anzeige ist bis zu 1g/ml linear mit einer Unsicherheit von 8%. Milligrammengen Chlorid oder Bromid bzw. Mikrogrammengen Jodid stören nicht. Die Menge Reaktionsprodukt läßt sich vervielfachen. Die Bestimmung von Jod und Jodid wird durch Zusatz von Kaliumjodat zu Ende geführt.

     

Simple ion chromatographic method for the determination of chlormequat residues in pears

Current methods for quantitative determination of chlormequat residues in food crops are characterized by rather low recoveries and the need for derivatization (in case of gas chromatography, GC), or by high capital investment (in case of liquid chromatography–mass spectrometry, LC–MS). We propose a cation-exchange chromatography method for the analysis of chlormequat in pears. The method is based on extraction of the target compound with 40 mM HCl, followed by centrifugation and filtration. The filtrate is directly injected into an ion chromatograph equipped with a commercially available cation-exchange column and a suppressed conductivity detection system. While the limit of detection (LOD) (0.5 mg/kg) may not be small enough to allow dietary analysis, the method meets all validation requirements and is an alternative for the existing GC and LC–MS methods in quality control.     

Simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method for the quantification of lacidipine in human plasma

A simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method was developed and validated for the quantification of lacidipine in human plasma using its structural analogue, amlodipine, as internal standard (IS). The method involves a simple single-step liquid-liquid extraction with tert-butyl methyl ether. The analyte was chromatographed on an Xterra MS C(18) reversed-phase chromatographic column by isocratic elution with 20 mM ammonium acetate buffer-acetonitrile (10:90, v/v; pH 6) and analyzed by mass spectrometry in the multiple reaction monitoring mode. The precursor to product ion transitions of m/z 456.4 --> 354.4 and m/z 409.3 --> 238.3 were used to measure the analyte and the I.S., respectively. The chromatographic run time was 1.5 min and the weighted (1/x(2)) calibration curves were linear over the range 0.1-25 ng ml(-1). Lacidipine was sensitive to temperature in addition to light. The method was validated in terms of accuracy, precision, absolute recovery, freeze-thaw stability, bench-top stability and re-injection reproducibility. The limit of detection and lower limit of quantification in human plasma were 50 and 100 pg ml(-1), respectively. The within- and between-batch accuracy and precision were found to be well within acceptable limits (<15%). The analyte was stable after three freeze-thaw cycles (deviation <15%). The average absolute recoveries of lacidipine and amlodipine (IS) from spiked plasma samples were 51.1 +/- 1.3 and 50.3 +/- 4.9%, respectively. The assay method described here could be applied to study the pharmacokinetics of lacidipine.     

Comparison of cholesterol oxidation product preparation methods for subsequent gas chromatographic analysis

An evaluation was made of the stability of cholesterol hydroperoxides (CHPs) under the analytical conditions and preparation methods commonly used for determination and quantification of cholesterol oxidation products (COPs). CHPs were prepared by photoxidation and separated by silica thin-layer chromatography. CHPs were individually collected by normal-phase liquid chromatography and then subjected either to reduction or to cold saponification. The corresponding hydroxyl derivatives were generated by reduction, whereas cold saponification gave rise predominantly to 7-ketocholesterol. In another test, silylated and non-silylated CHPs were separately injected into a gas chromatograph at 310 degrees C, collected, and re-injected into a gas chromatography-mass spectrometry system. The silylated CHPs were more stable than the non-silylated ones, giving 7-ketocholesterol, 7alpha- and 7beta-hydroxycholesterol as main degradation products. Two unknown degradation peaks were detected in both silylated and nonsilylated CHPs, having 384 as main m/z fragment. The study of their mass spectra led to the conclusion that peaks A and B correspond to 6alpha- and 6beta-hydroxycholesterol, respectively.