Determination of trace levels of fatty acid metal salts by high-performance liquid chromatography with fluorescence prelabeling

Determination of insoluble soap in agricultural soil and sewage sludge samples by liquid chromatography with ultraviolet detection

We have developed a new analytical procedure for determining insoluble Ca and Mg fatty acid salts (soaps) in agricultural soil and sewage sludge samples. The number of analytical methodologies that focus in the determination of insoluble soap salts in different environmental compartments is very limited. In this work, we propose a methodology that involves a sample clean-up step with petroleum ether to remove soluble salts and a conversion of Ca and Mg insoluble salts into soluble potassium salts using tripotassium ethylenediaminetetraacetate salt and potassium carbonate, followed by the extraction of analytes from the samples using microwave-assisted extraction with methanol. An improved esterification procedure using 2,4-dibromoacetophenone before the liquid chromatography with ultraviolet detection analysis also has been developed. The absence of matrix effect was demonstrated with two fatty acid Ca salts that are not commercial and are never detected in natural samples (C₁₃:₀ and C₁₇:₀). Therefore, it was possible to evaluate the matrix effect because both standards have similar environmental behavior (adsorption and precipitation) to commercial soaps (C₁₀:₀) to C₁₈:₀). We also studied the effect of the different variables on the clean-up, the conversion of Ca soap, and the extraction and derivatization procedures. The quantification limits found ranged from 0.4 to 0.8 mg/kg. The proposed method was satisfactorily applied for the development of a study on soap behavior in agricultural soil and sewage sludge samples.

Design and synthesis of a novel fluorescent reagent, 6-oxy-(ethylpiperazine)-9-(2'-methoxycarbonyl) fluorescein, for carboxylic acids and its application in food samples using high-performance liquid chromatography

A novel derivatization reagent for carboxylic acids, 6-oxy-(ethylpiperazine)-9-(2'-methoxycarbonyl)fluorescein (EPMF) has been well designed and synthesized. It was used to label 13 fatty acids, n-butyric acid (C4), n-valeric acid (C5), n-hexanoic acid (C6), n-heptanoic acid (C7), n-octanoic acid (C8), n-nonanoic acid (C9), n-decanoic acid (C10), lauric acid (C12), myristic acid (C14), palmitic acid (C16), stearic acid (C18), oleic acid (C18:1) and linoleic acid (C18:2), successfully. The derivatization reaction with fatty acids was completed at 50 degrees C, 50 min. The derivatives of fatty acids were separated on a C18 reversed-phase column with gradient elution and fluorescence detection at lambda(ex)/lambda(em)=469/518 nm. The detection limits obtained were 0.4-2 nmol L(-1) (signal-to-noise ratio of 3). The proposed method has been applied to the quantification of fatty acids in edible oil with recoveries over 93%. It has been demonstrated that EPMF is a prominent derivatization reagent for fatty acids and is suitable for HPLC.

Determination of long-chain fatty acids in bryophyte plants extracts by HPLC with fluorescence detection and identification with MS

A sensitive method for the determination of long-chain fatty acids (LCFAs) (>C20) using 1-[2-(p-toluenesulfonate)-ethyl]-2-phenylimidazole-[4,5-f]-9,10-phenanthrene (TSPP) as tagging reagent with fluorescence detection and identification with post-column APCI/MS has been developed. The LCFAs in bryophyte plant samples were obtained based on distillation extraction with 1:1 (v/v) chloroform/methanol as extracting solvent. TSPP could easily and quickly label LCFAs at 90 degrees C in the presence of K2CO3 catalyst in DMF. Eleven free LCFAs from the extracts of bryophyte plants were sensitively determined. Maximal labeling yields close to 100% were observed with a five-fold excess of molar reagent. Separation of the derivatized fatty acids exhibited a good baseline resolution in combination with a gradient elution on a reversed-phase Eclipse XDB-C8 column. Calculated detection limits from 1.0 pmol injection, at a signal-to-noise ratio of 3, were 26.19-76.67 fmol. Excellent linear responses were observed with coefficients of >0.9996. Good compositional data were obtained from the analysis of the extracted LCFAs containing as little as 0.2g of bryophyte plant samples. Therefore, the facile TSPP derivatization coupled with HPLC/APCI/MS analysis allowed the development of a highly sensitive method for the quantitation of trace levels of LCFAs from biological and natural environmental samples.

Fatty acid profiles of lipid samples

Most lipids are best characterized by their fatty acids which differ in chain length, the degree of unsaturation, configuration and position of the double bonds, and the presence of other functionalities. The fatty acid profiles are currently most frequently determined by capillary gas chromatography of the methyl esters which are prepared by a variety of methods. These are discussed with an emphasis on more recent developments, along with the stationary phases used for the separations and the methods employed for identification of the fatty acids. HPLC is applied less frequently for ascertaining fatty acid profiles than GC, but a very large number of derivatives for ultraviolet and fluorescence detection have been proposed. This method continues to evoke increasing interest, particularly in conjunction with fluorescence detection. This technique enables attainment of greater sensitivities than with standard GC methods employing flame ionization detection. Extensive applications of it to the analysis of free fatty acids in blood and other biomedical samples are clearly discernible. Other methods, including supercritical fluid chromatography, have found only limited application for fatty acid profiling.

Use of derivatization to improve the chromatographic properties and detection selectivity of physiologically important carboxylic acids

In this review, tagging techniques with reagents used for ultraviolet-visible (UV-Vis), fluorescent (FL), chemiluminescent (CL) and electrochemical detection (ED) for higher carboxylic acids in HPLC are evaluated in terms of the tagging reactions, handling, flexibility, stability of the reagents and the corresponding derivatives, sensitivity and selectivity. Emphasis is given to the applications of these tagging techniques to biologically important carboxylic acids of relatively high molecular mass including free fatty acids, prostaglandins, leukotrienes and thromboxanes etc. Some typical examples are described. Although RIA and GC-MS are powerful techniques for the highly sensitive determination of carboxylic acids, tagging for these techniques is not included in this review because recent progress in tagging methods has been mainly concerned with HPLC detection.

4-Bromomethyl-7-methoxycoumarin and analogues as derivatization agents for high-performance liquid chromatography determinations: a review

A major part of modern analytical problem solving deals with the trace level determination of organic compounds and contaminants in biomedical, food and environmental samples. In the analysis of these samples chromatographic techniques play a predominant role. Unfortunately, however, even the combined force of an efficient separation plus a sophisticated mode of detection does not always create sufficient selectivity and/or sensitivity for the final goal to be attained. In such cases, special attention has to be devoted to derivatization or conversion of the analyte(s) of interest (for improved detection selectivity and/or sensitivity) and sample pretreatment (for trace enrichment and clean-up). The above is especially true when, as is often the case today, relatively polar drugs, endogenous compounds, additives or environmental pollutants and/or their (bio)-degradation products have to be determined. For such classes of compounds high-performance column liquid chromatography (HPLC) generally is the preferred method of separation. Reversed-phase HPLC with fluorescence detection is a powerful means of analysis for compounds which possess native fluorescence. They are, however, relatively few in number. In order to make the method useful for a much wider range of analytes, one can therefore resort to derivatization (labelling) or other means of analyte conversion to obtain highly fluorescent reaction products, which can then be detected with the required selectivity and sensitivity. 4-Bromomethyl-7-methoxycoumarin is often used as fluorescent label for the determination of compounds possessing a carboxylic group. About 8% of the biologically interesting analytes--ranging from polar amino acids and peptides to apolar fatty acids--possess such a group.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex- and age-related variations in the in vitro heparin-releasable lipoprotein lipase from mononuclear leukocytes in blood

An in vitro heparin release of lipoprotein lipase (LPL) from whole blood, mainly from monocytes, was demonstrated by (1) the time-course of lipolytic activity with the presence of 10 U/ml heparin at 37 degrees C, (2) the distribution of LPL activity in monocyte and lymphocyte fractions, (3) an immuno-inactivation with anti-LPL immunoglobulin (IgG) and (4) responses to various compounds such as NaCl, protamine sulfate, heparin, and serum activator. The in vitro heparin-releasable LPL activity from blood correlated well with the LPL activity of postheparin plasma obtained from both normolipidemic and hyperlipidemic rabbits. Studies in humans revealed sex- and age-related variations in the in vitro heparin-releasable LPL from monocytes in the blood of 134 normal subjects and 24 hypertriglyceridemic subjects: The mean LPL activity was significantly higher in normal females over the age of 30, than in the corresponding males. In the hypertriglyceridemic group, the LPL activity was also higher in females than in males, but it was not significant. The in vitro heparin-releasable LPL activity from monocytes in blood was comparable to the LPL activity derived from adipose tissue and postheparin plasma, and thus it reflects lipoprotein metabolism.

High-performance liquid chromatographic analysis of glucuronic acid conjugates after derivatization with 4-bromomethyl-7-methoxycoumarin

In order to enhance the detection sensitivity of various glucuronic acid conjugates (phenol, menthol borneol, estrone and testosterone) in high-performance liquid chromatography (HPLC), the compounds were esterified with 4-bromomethyl-7-methoxycoumarin in the presence of potassium carbonate and 18-crown-6 in acetone. The resulting esters were chromatographed on either a normal-phase (NP) column (LiChrospher DIOL) with hexane-ethanol mixtures as eluents or a reversed-phase column (LiChrospher CH-18) with methanol-water mixtures. They were detected by UV spectrophotometry at 328 nm. The structure of the derivatives was confirmed by mass spectrometry by direct introduction and chemical ionization. Prior to this step, their isolation on a semi-preparative scale was performed by NP-HPLC. The extraction of the studied glucuronides from microsomal solutions was tested by ion-suppression and ion-pair liquid-liquid partition and liquid-solid chromatography (on octadecylsilica cartridges). Extraction and chromatographic data are discussed with regard to the determination of glucuronyltransferase activity towards the aglycones cited above.