An optimized direct method for the determination of carboxylic acids in beverages by HPLC

Summary A direct method for the simultaneous determination of tartaric, malic, lactic, acetic, citric, shikimic, fumaric and succinic acids in fruit juices and wines by isocratic reversed phase HPLC is reported.The variables (pH, ionic strength, flow and temperature) have been optimized by a modification of the original simplex method. The separation factor (s) and calibrated resolution product (r^*) have been used as criteria for selectivity optimization. After validation, the method has been applied to the determination of carboxylic acids in apple, orange and lemon juices, white and red wines and musts during the fermenation process.     

Determination of inorganic anions, carboxylic acids and amino acids in plant matrices by capillary zone electrophoresis

Summary Physiological investigations of solute transport in plants affords knowledge of solute distribution between different tissues. Capillary electrophoresis using indirect UV and laser induced fluorescence (LIF) detection is demonstrated as a useful technique for the simultaneous determination of inorganic anions, amino acids and carboxylic acids in plant samples. Cell sap obtained from plant tissues as well as simple ethanolic or aqueous plant extracts can be analysed directly without any pretreatment. This matrix stability and the very small volumes required allow fast determinations of various compounds in small plant tissue sections. In the case of carboxylic acids, resolution can be optimized using calcium for selective complexation of some of the compounds. Selective and sensitive determination of amino acids is possible using precolumn derivatisation with orthophthaldialdehyde (OPA) and laser induced fluorescence detection. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Simulataneous determination of carboxylic acids and carbonyl compounds in estuaries by HPLC

Summary A method for the determination of 22 low relative molecular mass oxocarboxylic acids and carbonyl compounds in estuarine and marine samples is described. After derivatization of 5 ml samples with 2,4-dinitrophenylhydrazine separation is performed on a RP-18 column by gradient elution and with UV-detection. The detection limit ranges from 17 ngl⁻¹ (glycolaldehyde) to 500 ngl⁻¹ (cyclohexanone). The method was established for routine analysis of samples taken in an estuarine ecosystem but can be used for other aqueous systems as well.     

Simultaneous determination of inorganic and organic acids in air by use of annular denuders and ion chromatography

Summary The performance of KOH-coated annular denuders for simultaneous collection of gas-phase atmospheric organic and inorganic acids has been evaluated by ion chromatography (IC) with an NaOH−H₂O gradient. Sampling efficiency was tested for formic and acetic acids under dry and humid air conditions. With this method several mono- and dicarboxylic acids, nitric acid, and hydrogen chloride can be detected. Laboratory and field measurements confirmed the reliability of the denuder method and its superior versatility compared with other techniques (scrubbing by means of a nebulizer, cryogenic trapping) which cannot be used to determine termine gaseous inorganic acids.     

Robustness study of a reversed-phase liquid chromatographic method for the analysis of carboxylic acids in industrial reaction mixtures

The robustness study of the reversed-phase liquid chromatographic method developed for the quantitative analysis of carboxylic acids is a real asset to prepare method transfer because it provides an indication of its reliability during routine use. Indeed, it was possible to predict the consequences of small variations in operating conditions on the responses. The design of experiments approach was applied to model the effects and interactions of a high number of factors varying simultaneously with a limited number of runs. First we identified the factors which potentially affect the chromatographic responses used for carboxylic acids quantitation: detection wavelength (λ), column temperature (T), acetonitrile ratio in mobile phase (Me), duration of the plateau before the gradient (L) and gradient slope (S). Then we estimated the order of magnitude of realistic variations to assign factor levels. Finally a central composite design was carried out around the nominal conditions defined during method optimization. The statistical treatment of responses (retention factors, and concentrations) showed that the column temperature, the acetonitrile ratio in the mobile phase, the duration of the plateau before the gradient and the gradient slope were the most influent factors. The building of the robust domain from response-surfaces allowed us to give tolerance limits for the factors (216 nm < λ < 222 nm, 49.3 °C < T < 51.4 °C, 4.90% < Me < 5.18%, v/v, 4.5 min < L < 5.4 min, 9% < S < 11%) for which the performances of the method were maintained.     

2-Bromoacetyl-6-methoxynaphthalene: A useful fluorescent labelling reagent for HPLC analysis of carboxylic acids

Summary The use of 2-bromoacetyl-6-methoxynaphthalene as a fluorogenic labelling reagent in pre-column derivatization for the HPLC separation of biologically active carboxylic acids (fatty acids and bile acids) has been investigated. The compound reacts (30 min. at 70°C) with carboxylic acids to give fluorescent esters that can be separated by reversedphase HPLC and detected at ex. 300 nm, em. 460 nm. The experimental conditions for the derivatization and chromatographic separation are discussed. Applications to the determination of valproic acid and chenodeoxycholic acid in pharmaceutical formulations are described.     

Optimization of the derivatization method for the liquid-chromatographic determination of carboxylic acids in wines

Several reagents and experimental conditions were tested to optimize the yield of the derivatization procedure for determining carboxylic acids in wines. Two techniques were applied for optimization: a modified sequential simplex method and a simultaneous modelling method. The results obtained were similar; advantages of the latter method are discussed. The optimized conditions (phenacyl bromide as reagent with 18-crown-6 as catalyst with a reaction time of 90 min at 90 ° C) were used to determine the main carboxylic acids in several varietal wines of the Tarragona region.     

A rapid HPLC method for the determination of carboxylic acids in human urine using a monolithic column

A rapid HPLC method for the determination of carboxylic acids in urine samples using a Chromolith Performance RP/18e 100/4.6 with Chromolith Guard Cartridge RP/18e 10/4.6 (Merck KgaA, Darmstadt, Germany) was developed. The method facilitates the simultaneous determination of aromatic hydrocarbon metabolites mandelic acid (MA) and phenylglyoxylic acid (PGA) from styrene and ethylbenzene, hippuric acid (HA) from toluene and 2-, 3-, 4-methylhippuric acids (MHA) from xylene. 3-Hydroxybenzoic acid (3-HBA) was used as internal standard. A chromatographic run is completed within less than 5 min for styrene, ethylbenzene and toluene metabolites, and within 10 min for xylene metabolites. The detection limits are 9 mg L^–1 urine for MA, 1.25 mg L^–1 urine for PGA, 4.9 mg L^–1 urine for HA, 22 mg L^–1 urine for 2-MHA, and 18.5 mg L^–1 urine for 3-MHA.No significant differences of the MA, PGA and HA concentrations in human urine samples obtained by HPLC chromatography on LiChrosorb RP 18 and on Chromolith RP/18e columns were found. The results were evaluated by using ANOVA.Abbreviations MA mandelic acid - PGA phenylglyoxylic acid - HA hippuric acid - MHA methylhippuric acid - 3-HBA 3-hydroxybenzoic acid - ANOVA analyses of variance - GC gas chromatography - HPLC high-performance liquid chromatography     

Selection of optimal pH and solvent composition for the separation of organic acids using three-dimensional diagrams and a computer program

Summary The retention behaviour of different types of organic acids was investigated on an ODS-Hypersil column using eluents of various pH and of various methanol-water ratios. Equations introduced by Horvath and coworkers were fitted onto the experimental data, and the obtained constants were used to calculate the three-dimensional k′-surfaces for the compounds in the investigated pH and solvent composition range. Using the data of the individual surface diagrams the optimal pH and solventg composition was computed for the separation of six selected compounds. To verify the applicability of the above procedure the chromatographic separation of the six compounds was carried out with the predicted conditions, and the chromatogram obtained is presented.     

Precolumn fluorogenic labelling of carboxylic acids with the use of N-(1-pyrenyl)-bromoacetamide and phase-transfer catalysis

Summary N-(1-Pyrenyl)-bromoacetamide, which is readily synthesized from 1-aminopyrene and bromoacetyl bromide, has proved to be an excellent derivatization reagent for carboxylic acids. A technique has been developed, based upon a reaction with the carboxylate as an ion pair in ethylene dichloride at 90 °C, which gives highly fluorescent ester derivatives, permitting quantitative determination by liquid chromatography of less than one pmol using conventional fluorimetric detection. Further, the method is highly reproducible and of general utility.     

Determination of the enantiomeric composition of chiral carboxylic acids using chiral derivatization and HPLC

Summary The enantiomers of chiral carboxylic acids were separated as their diastereomeric amides with (1R,2R)-(−)-1-(4-nitrophenyl)-2-amino-1,3-propanediol (“levobase”) and with “dextrobase” (the enantiomer of levobase) by high-performance liquid chromatography using a conventional C-18 column and various solvent systems containing acetonitrile, methanol, water, and phosphoric acid.     

High-performance liquid chromatographic determination of major organic acids in apple juices and ciders

Summary A reversed-phase high-pressure liquid chromatographic method is presented for the simultaneous separation and determination of malic, citric, lactic, succinic and ascorbic acids in apple juices and ciders. After filtration and/or degasification, the organic acids in the sample are separated on a LiChrosorb/C₁₈ column and quantified by using a rapid diode array detector. The method is considered to be a suitable choice for the accurate and precise determination (C.V. 5%) of these compounds.     

Simultaneous determination of cefoxitin,cefuroxime, cephalexin and cephaloridine in plasma using HPLC and a column-switching technique

Summary A new high performance liquid chromatographic method was developed using a column-switching technique for the simultaneous determination of cephalexin, cefuroxime, cefoxitin and cephaloridine in plasma. The plasma samples were injected onto a precolumn packed with Corasil RP C₁₈ (37–50 m) after simple dilution with an internal standard solution in 0.01 M acetate buffer (pH 3.5). Polar plasma components were washed out using 0.01 M acetate buffer (pH 3.5). After valve switching, the concentrated drugs were desorbed in back-flush mode and separated on a Partisil ODS-3 column using acetonitrile in 0.02 M acetate buffer (pH 4.3) (1585, v/v) as the mobile phase. The method showed excellent precision with good sensitivity and speed with a detection limit of 0.5 g/ml. The total analysis time per sample was less than 25 min, and the mean coefficients of variation for intra- and inter-assay were both less than 4.9 %.This method has been successfully applied to plasma from rats after subcutaneous injection of cefuroxime.     

离子排斥色谱用于厌氧消化处理水中脂肪族羧酸的分析（英文）

The analysis of seven aliphatic carboxylic acids(formic,acetic,propionic,iso-butyric,n-butyric,iso-valeric and n-valeric acid) in anaerobic digestion process waters for biogas production was examined by ion-exclusion chromatography with dilute acidic eluents(benzoic acid,perfluorobutyric acid(PFBA) and sulfuric acid) and non-suppressed conductivity/ultraviolet(UV) detection.The columns used were a styrene/divinylbenzene-based strongly acidic cation-exchange resin column(TSKgel SCX) and a polymethacrylate-based weakly acidic cation-exchange resin column(TSKgel Super IC-A/C).Good separation was performed on the TSKgel SCX in shorter retention times.For the TSKgel Super IC-A/C,peak shape of the acids was sharp and symmetrical in spite of longer retention times.In addition,the mutual separation of the acids was good except for iso-and n-butyric acids.The better separation and good detection was achieved by using the two columns(TSKgel SCX and TSKgel Super IC-A/C connected in series),lower concentrations of PFBA and sulfuric acid as eluents,non-suppressed conductivity detection and UV detection at 210 nm.This analysis was applied to anaerobic digestion process waters.The chromatograms with conductivity detection were relatively simpler compared with those of UV detection.The use of two columns with different selectivities for the aliphatic carboxylic acids and the two detection modes was effective for the determination and identification of the analytes in anaerobic digestion process waters containing complex matrices.     

Quantitative HPTLC analysis of carboxylic acids in wine and juice

The need for quick and specific assay of carboxylic acids in wine and non-fermented beverages is explained. The method developed in this work is based on high performance thin-layer chromatography (HPTLC) followed by densitometric evaluation. Untreated samples, with the exception of red wines which were destained, were directly sprayed onto the cellulose layer. The chromatogram was developed with ethyl acetate-toluene-water-formic acid 60:20:20:15, then stained with xylose-aniline reagent. Densitometric scanning is by absorbance at 546 nm. The method is quick, sensitive, and has a wide dynamic range for the acids analyzed.     

Full automation of serotonin determination by column-switching and HPLC

Summary A simple, fast, fully automated method for plasma serotonin determination is described. Full automation is obtained by coupling two devices: a sample processing station and a solid-phase autosampler. The sample processing station dilutes the plasma sample and is then connected, on-stream, with the solid-phase autosampler. It firstly fills a loop with all the solvents necessary for the sample clean-up, then, inverting the flow, pumps these solvents through the silica-bonded cation-exchange disposable extraction cartridge positioned on the autosampler. For the elution, the cartridge is switched on-stream with the HPLC analytical column and serotonin is eluted by the HPLC mobile-phase. The HPLC separation is performed by ion-pairing reversed-phase liquid chromatography. The column effluent is completely reduced by an electrochemical reactor and serotonin is detected in an oxidation-mode by a dual-cell electrochemical detector. The plasma sample is 50 l, the plasma sensitivity is 40 ng/l, the retention time is 6 min and the recovery is 95%. The repeatibility, the normal ranges for platelet-poor and for platelet-rich plasma have been established and correlation with manual HPLC calculated.Presented at the 17th International Symposium on Chromatography, September 25–30, 1988, Vienna, Austria.     

Simultaneous determination of CGP 22 848 and its major metabolite (free carboxylic acid) CGP 35 652 in plasma by HPLC

Summary A specific method for the quantitative determination of CGP 22 848 (a basic compound) and its major metabolite CGP 35 652 (a free carboxylic acid metabolite) in plasma using CGP 17 582 as internal standard is described. Separation of components is by reversed-phase chromatography using a mobile phase consisting of pH 3 phosphate buffer-acetonitrile (76:24, v/v) at a flow-rate of 1 ml/min in conjunction with a Radialpak C18 cartridge combined with a radial compression separation system or by using a mobile phase consisting of pH 3 phosphate buffer-acetonitrile (80:20, v/v) at a flow-rate of 0.8 ml/min in conjunction with a Novapak C18 column. Rapid extraction of CGP 22 848 and CGP 35 652 from plasma is achieved using reversed-phase C18 columns (Bond-Elut or Supelco). With 250 μl of plasma, concentrations down to 0.078 μM (25 ng/ml) of CGP 22 848 B and 0.326 μM (100 ng/ml) of CGP 35 652 A can be determined. A wavelength of 221 nm was used to monitor CGP 22 848, 280 nm for CGP 35 652 and 320 nm for the internal standard.     

HPLC determination of rhodamine B (C.I. 45170) in cosmetic products

Summary A method is proposed for the extraction, separation, identification and quantitative measurement of rhodamine B in cosmetics samples The colour is extracted with a solution of orthophosphoric acid in either water or DMF (depending on the type of cosmetic) adsorbed on a polyamide column, and then eluted with water and methanol. Further clean-up of the extract is performed by means of a Bond Elut C-18 cartridge, from which rhodamine B is eluted with methanol-water (82). The final eluate is examined by HPLC. Chromatography is performed on a C-18 column with a gradient elution from 5050 to 7030 of acetonitrile-water, containing 0.1 M sodium perchlorate, in 15 min. A diodearray detector enables peak purity analysis. The method gives recovery values of approximately 90%, or better, and the reproducibility is within 4%.     

HPLC method for determination of cefuroxime in plasma

Summary This paper describes an HPLC method for the determination of cefuroxime in human plasma. The method uses solid phase extraction (SPE) and has acceptable sensitivity, precision and accuracy. The limit of quantification in plasma samples is 0.1 μg mL⁻¹. Calibration curves were linear within 0.1–20 μg mL⁻¹, with mean correlation coefficient of 0.9982. Mean inter day precision and accuracy were 7.8% and 6.4%, respectively. The method was applied to determine cefuroxime levels in patients receiving cefuroxime, 3 time per day.     

HPLC determination of non-ionic surfactants used in tertiary oil recovery

Summary Having developed a chromatographic technique with a diol bonded phase for the study of the distribution versus ethylene oxide number (E.O.) for various non-ionic polyoxyethylated surfactants used in enhanced oil recovery (KL 6, ; KM 11, and KM 20, ) we report here the titration of one of these surfactants (KL 6) in the presence of an ionic surfactant (S 385, sulfonated petroleum fraction) and other non-ionic surfactants (KM 11 and/or KM 20) which are the conditions found in enhanced oil recovery. This work has been carried out in brine and in n-decane, as a model for the petroleum phase. Obviously in the case of aqueous phases it was necessary to carry out a thorough dehydration before the chromatographic analyses. We have shown that it is possible, under these conditions, to determine the KL 6 surfactant in the concentration range 500 to 6000 ppm with a precision of 70 ppm without experiencing interference from KM 11 or KM 20 non-ionic surfactants or S 385 ionic surfactant. Furthermore, from some of the samples studied which were in contact with the rock shale, we showed that strong adsorption of the KL 6 occurs. Chromatographic analyses show that this surfactant is only desorbed from the rock shale when employing a non-ionic surfactant such as KM 25 which is much more polar than the KL 6.