Liquid chromatographic retention and separation of phenols and related aromatic compounds on reversed phase columns

Summary Isocratic column liquid chromatographic systems with UV absorbance detection at 280 nm have been developed for the separation of 29 phenolics and related compounds.The selectivity was investigated on silica-, carbon- and polymer-based separation columns for the separation of phenolic type of components. The effects of various acetonitrile/buffer mixtures, and pH of the mobile phase, and their impact on the retention of the phenols was assessed. Tables of retention times on the four columns for the 29 phenols with two different acetonitrile/buffer mixtures, together with the retention times at three pHs from 6.5 to 2.3 with varying levels of organic modifier on the LiChrospher RP 18 column are presented.As an application, the analysis of real river water samples from the Ebro river is described using a solid phase extraction step prior to injection into the chromatographic system.     

Gas chromatographic determination of vapour pressure and related thermodynamic properties of monoterpenes and biogenically related compounds

The (subcooled) liquid vapour pressure, heat of vapourization and gas-liquid heat capacity difference of monoterpenes and biogenically related compounds were determined by a gas-liquid chromatographic method based on Kovats retention indices. Compared to those used in previous studies using the same method, these compounds are structurally diverse and have relatively low boiling points. Despite of this and even though the difference in activity coefficients in the chromatographic column stationary phase between the test and reference compounds were ignored, results for vapour pressure compare favorably with experimental literature data. The results indicate that the method can be improved by introducing temperature dependent activity coefficients, preferably based on a physicochemical model for gas-liquid partitioning.     

Development and validation of an RP-HPLC method for quantitative determination of vanillin and related phenolic compounds in Vanilla planifolia

A simple and fast method was developed using RP-HPLC for separation and quantitative determination of vanillin and related phenolic compounds in ethanolic extract of pods of Vanilla planifolia. Ten phenolic compounds, namely 4-hydroxybenzyl alcohol, vanillyl alcohol, 3,4-dihydroxybenzaldehyde, 4-hydroxybenzoic acid, vanillic acid, 4-hydroxybenzaldehyde, vanillin, p-coumaric acid, ferulic acid, and piperonal were quantitatively determined using ACN, methanol, and 0.2% acetic acid in water as a mobile phase with a gradient elution mode. The method showed good linearity, high precision, and good recovery of compounds of interest. The present method would be useful for analytical research and for routine analysis of vanilla extracts for their quality control.     

RP-HPTLC densitometric determination and validation of vanillin and related phenolic compounds in accelerated solvent extract of Vanilla planifolia*

A simple, fast and sensitive RP-HPTLC method is developed for simultaneous quantitative determination of vanillin and related phenolic compounds in ethanolic extracts of Vanilla planifolia pods. In addition to this, the applicability of accelerated solvent extraction (ASE) as an alternative to microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE) and Soxhlet extraction was also explored for the rapid extraction of phenolic compounds in vanilla pods. Good separation was achieved on aluminium plates precoated with silica gel RP-18 F(254S) in the mobile phase of methanol/water/isopropanol/acetic acid (30:65:2:3, by volume). The method showed good linearity, high precision and good recovery of compounds of interest. ASE showed good extraction efficiency in less time as compared to other techniques for all the phenolic compounds. The present method would be useful for analytical research and for routine analysis of vanilla extracts for their quality control.     

Liquid chromatographic determination of the enantiomeric composition of amphetamine and related drugs by diastereomeric derivatization

A procedure is described for the derivatization of amphetamine and methamphetamine enantiomers with 4-nitrophenylsulfonyl-(S)-prolyl chloride. The resulting diastereomeric amphetamine derivatives were resolved by a reversed-phase procedure. The derivatization yield was maximized in the 95% range using a five-fold molar excess of the chiral derivatizing agent and an approximate 18 to 1 ratio of base (NaHCO3) to total acid generated in the reaction.     

Automated sample preparation and chromatographic analysis: determination of CGS 10787B and related compounds

An automated method is described for analyzing biological samples originating from CGS 10787B drug disposition studies. The method incorporates a laboratory robot to prepare plasma and urine samples and a high performance liquid chromatographic system to simultaneously analyze for CGS 10787B, as well as metabolites and drug-related compounds (CGS 12094, CGS 17000, and CGS 17001). The robot allquots the biological sample, adds an internal standard, and performs all the steps necessary for the liquid-liquid extraction and concentration of the drug and related components, while operating unattended around the clock. Recovery and reproducibility assessments indicate good accuracy and precision for the method. The limits of detection for the method are 0.2 microgram/mL in plasma and 0.5 microgram/mL in urine, for all components.     

Liquid chromatographic method with fluorescence detection for the determination of polycyclic aromatic hydrocarbons in environmental samples

A method for the determination of some polynuclear aromatic hydrocarbons (PAHs) in water samples and air filters is presented. Samples were extracted with light petroleum-diethyl ether (85 + 15) and the extracts were concentrated before analysis. Reversed-phase liquid chromatography with fluorescence detection was applied to separate and determine the PAHs. Recoveries of individual PAHs from spiked water samples were 0.16–0.27 ng ml^?1. Detection limits in the picogram range were obtained for each compound.     

Liquid chromatographic determination of nicarbazin in feeds

A new liquid chromatographic method has been developed for determination of nicarbazin in feeds. Approximately 40 g feed is extracted with 200 mL acetonitrile-water (80 + 20, v/v). An aliquot of the extract is filtered and assayed using a reversed-phase isocratic method that measures the 4,4'-dinitrocarbanilide moiety of nicarbazin at a wavelength of 340 nm. For medicated feeds, the method uses a standard linear range of 5 to 100 microg/mL. For lower levels, a linear range of 50 to 150 ng/mL can be used. The method has a limit of detection of 250 ng/g and a limit of quantitation of 500 ng/g in a 40 g feed sample. Recovery was 99.1%, with a range of 95.2 to 101.8%. In the typical U.S. dosing range of 27 to 113.5 g/ton, the precision of the method based on one analyst, one day, and 2 weighings ranged from 2.8% (113.5 g/ton) to 4.7% (27 g/ton).     

Liquid chromatographic determination of triasulfuron in soil

Two extraction methods were developed for the determination of triasulfuron in soil. Method I included extraction with methanol-phosphate buffer at pH 7 (2 + 1, v/v), liquid-liquid partition with dichloromethane, and cleanup on a liquid chromatographic Si adsorption solid-phase extraction tube. In Method II, Extrelut was added and the sample was then extracted with acetonitrile. In both cases, the extracts were analyzed by liquid chromatography (LC) with UV detection and the LC peak was confirmed by LC/mass spectrometry (MS). The 2 methods were tested on 3 soils having different physicochemical characteristics. Method I gave 83% average recovery and a determination limit of 0.4 microg/kg soil. Method II gave 67% average recovery and a determination limit of 2 microg/kg soil. Examples of application of Method I to field samples are reported.     

Liquid chromatographic determination of trimethylamine in water

A method for the selective determination of trimethylamine (TMA) in aqueous matrices by liquid chromatography is reported. The proposed procedure is based on the derivatization of the analyte with 9-fluorenylmethyl chloroformate (FMOC) in a precolumn (Hypersil C18, 30 microm, 20 mm x 2.1 mm i.d.) connected on-line to the analytical column (LiChrosphere 100 RP18, 5 microm, 125 mm x 4 mm i.d.). Gradient elution was performed with a mixture of acetonitrile-water-0.05 M borate buffer (pH 9.0). The method has been applied to the direct determination of TMA in water within the 0.25-10.0 microg/ml concentration interval, and can also be adapted to the determination of TMA over the range 0.05-1.0 microg/ml by incorporating a preconcentration stage with C18 solid-phase extraction (SPE) cartridges. Good linearity, reproducibility and accuracy was achieved within the tested concentration intervals. The limits of detection at 262 nm were 50 and 5 ng/ml for the direct method and for the method involving preconcentration, respectively. The proposed conditions allowed the selective determination of TMA in the presence of other primary and secondary short-chain aliphatic amines. The utility of the described procedure has been tested by determining TMA in different water samples.     

Liquid chromatographic determination of flumetsulam in soybeans

A liquid chromatography (LC) method with UV detection is reported for the determination of the sulfonamide herbicide flumetsulam in soybeans. The ground soybean sample was partitioned between methanol and hexane. The hexane removed the lipids, and the methanol layer containing the analyte was further partitioned between dichloromethane and aqueous phosphate buffer at pH 7.0. The aqueous layer, containing the analyte, was acidified to pH 2.2 and partitioned with fresh dichloromethane. The dichloromethane layer containing the analyte was evaporated, and the residue was dissolved in the LC mobile phase for analysis. A polar embedded C18 column was used with a mobile phase of pH 2.2 aqueous phosphate buffer-acetonitrile (68 + 32), run isocratically with detection at 225 nm. The average recovery was 82% with a relative standard deviation (RSD) of 10%. A coefficient of determination of R2 = 0.9992 was achieved for the analyte calibration curve, from 0.005 to 1 microg/mL. The limit of detection, determined from 3 times the standard deviation of 7 replicate extractions of the lowest fortification level (0.01 microg/g), was 0.005 microg/g with an RSD of 22%. LC/electrospray ionization/mass spectrometry in the positive-ion mode was used for identity confirmation of flumetsulam in the fortified soybean extract. The ions at m/z 326, 348, and 129 were observed.     

Liquid chromatographic purification and detection of anabolic compounds.

The role of liquid chromatography within methods of analysis for steroids, related compounds and beta-agonists in biological samples is discussed. Special attention is given to the application of liquid chromatography in sample preparation and extract clean-up. Different forms of liquid chromatography, including immunoaffinity chromatography, are compared and evaluated. Methods for confirmation based on gas chromatography-mass spectrometry and cryotrapping Fourier transform infrared spectrometry are discussed.     

Gas chromatographic separation of some labelled aromatic halogen compounds

Gas—liquid-chromatographic techniques for the separation of a large variety of mono-, di-and polysubstituted benzene derivatives from their multicomponent systems have been developed for the study of reactions of recoil halogen atoms with aromatic compounds. The¹⁸F,^34mCl,³⁸Cl,⁸²Br and¹²⁸I labelled benzene derivatives were produced by neutron irradiations of the corresponding liquid mixtures. Because of the short half-life of most of the isotopes in question a relatively fast method was required, therefore each of the techniques described takes less than one hour to achieve the separation.     

Liquid chromatographic methods for chloral hydrate determination

Liquid chromatographic methods, based on reversed-phase (RP) and anion-exchange mechanisms, have been developed for chloral hydrate determination. Both methods are preceeded by derivatization of chloral hydrate. For RP separations, different reagents [namely dansylhydrazine and o-(4-nitrobenzyl)hydroxylamine] have been studied, but the best results have been achieved using 1,2-benzenedithiol with UV detection at 220 nm. The anion-exchange method is based on derivatization with NaOH to form sodium formate that is then analyzed by anion-exchange, with suppressed conductivity detection. Derivatization conditions were optimized in order to reach the best yield of reaction. The optimization of the procedure allowed to determine chloral hydrate with detection limits as low as 0.2 μg/l with good linearity and reproducibility. The anion-exchange method was also applied for chloral hydrate determination in a drinking water sample. A preconcentration procedure has also been studied.     

Liquid chromatographic determination of iprovalicarb in cabbage and soil

A method was developed for the determination of iprovalicarb, a new carbamic acid-amino acid fungicide, by liquid chromatography with UV detection. The method uses a reversed-phase C18 column with lambdamax at 215 nm and methanol-water (72 + 25, v/v) as the mobile phase. Cabbage head and leaves fortified with iprovalicarb were extracted with acetone. Partitioning of the fungicide into dichloromethane was followed by column cleanup on neutral alumina. Fortified soil samples were extracted with acetonitrile, and the extract was subjected to column cleanup. The average recoveries of iprovalicarb from cabbage head, leaves, and soil were 86.50, 82.0, and 84.3%, respectively, for fortification levels of 1 and 2 microg/g for cabbage head and leaves and 2 and 4 microg/g for soil.     

Liquid chromatographic determination of sulindac and metabolites in serum

An improved liquid chromatographic procedure is described for the quantitative determination of sulindac, sulindac sulfone, and sulindac sulfide from serum. The procedure makes use of acetonitrile extraction of the compounds of interest from acidified serum samples. Under these conditions extraction efficiencies in the 85 percent range are obtained for each of the compounds. The liquid chromatographic separation of the compounds of interest and the internal standard (indomethacin) is accomplished in an isocratic elution procedure using a nitrile (CN) stationary phase. The HPLC separation procedure is completed in less than 10 minutes, giving excellent resolution and peak shape.