9(chloromethyl)anthracene: a useful derivatizing reagent for enhanced ultraviolet and fluorescence detection of carboxylic acids with liquid chromatography

Fluorescent palladium(II) and platinum(II) NHC/1,2,3-triazole complexes: antiproliferative activity and selectivity against cancer cells

Fluorescent Pd(ii) and Pt(ii) complexes bearing 4-methylene-7-methoxycoumarin (MMC) and 2,6-diispropylphenyl (Dipp) substituted NHC/1,2,3-triazole hybrid ligands are described. Depending on the reaction conditions two different ligand coordination modes are observed, i.e., bidentate solely coordinating via NHCs or tetradentate coordinating via NHCs and 1,2,3-triazoles. All Dipp substituted complexes show antiproliferative activity against cervix (HeLa) and breast (MCF-7) human carcinoma cells. The activity significantly depends on the coordination mode, with the tetradentate motif being notably more effective (HeLa: IC50 = 3.9 μM to 4.7 μM; MCF-7: IC50 = 2.07 μM to 2.35 μM). Amongst the MMC series, only the Pd(ii) complex featuring the bidentate coordination mode is active against HeLa (IC50 = 6.1 μM). In contrast to its structurally related Dipp derivative (SI = 0.6), it shows a high selectivity for HeLa (SI > 16) compared to healthy skin cells (HaCaT). According to fluorescence microscopy, this compound is presumably located in late endosomes or lysosomes.

Design of Pyrene-Fatty Acid Conjugates for Real-Time Monitoring of Drug Delivery and Controllability of Drug Release

Fluorescence probes are usually employed to analyze pharmacokinetics of drug carriers; however, this method using usual probes is not suitable to monitor drug carriers in detail because fluorescence spectra do not change by the disruption of drug carriers. In this study, pyrene-fatty acid conjugates were investigated as probes to monitor the state of drug carriers in real time. 1-Pyrenemethanol was conjugated with fatty acids, such as lauric acid, stearic acid, and behenic acid, and the conjugates were stirred in ethanol, resulting in the formation of submicron particles; these particles exhibited excimer emission. When J774.1 and Colon 26 cells were treated with these particles, the associated fluorescence spectra shifted from excimer emission to monomer emission. Moreover, the degree of change was controlled by the type of fatty acid. These results support the design of drug carriers that can be used to monitor pharmacokinetics in real time and to control the disruption time.

Development and validation of a novel derivatization method for the determination of lactate in urine and saliva by liquid chromatography with UV and fluorescence detection

We developed a novel and straightforward derivatization method for the determination of lactate by reversed phase high-performance liquid chromatography (RP-HPLC) with fluorescence and UV detection in biological matrices as urine and saliva. The derivatization of lactate was achieved employing 9-chloromethyl anthracene (9-CMA) as fluorescence reagent, which has never been previously used to obtain a lactate derivative. Lactate reacts with 9-CMA with high selectivity in a very short time, without requiring extraction procedures from the aqueous solution, and the reaction reaches 70% completion in 30 min. The ester derivative obtained can be easily determined by RP-HPLC with fluorescence detection at 410 nm (λ ex=365 nm) and UV detection at 365 nm. The method was also optimized in order to allow for the simultaneous determination of lactate and creatinine for the application to urine samples. The lactate calibration curve was linear in the investigated range 2 × 10(-4)-3 × 10(-2)mM and the limit of detection, calculated as three times the standard deviation of the blank divided by the calibration curve slope, was 50 nM for both fluorescence and UV detection. Intra-day and inter-day repeatability were lower than 5% and 6%, respectively. The method proposed was successfully applied to the analysis of urine and saliva samples.

Determination of fatty acids in vegetable oil by reversed-phase liquid chromatography with fluorescence detection

The effect of temperature and organic solvent composition (acetonitrile and methanol) on the reversed-phase separation of coumarin-derivatized fatty acids according to their carbon number (C14 to C22), the degree of unsaturation, as well as cis/trans (C18:1 c/t, C18:2 cc/tt, C18:3 ccc/ttt) configuration was investigated to find out the effective separation condition. Based on the linear plots of the logarithm of the capacity factor of saturated fatty acids versus their carbon number, the equivalent chain length (ECL) of unsaturated fatty acids was calculated. The ECL values were found to be significantly altered and the differentiation between cis and trans fatty acids was increased when either the temperature or organic solvent composition was decreased. These results generally led to a better resolution at the expense of separation time. A ternary gradient composed of water, acetonitrile, and methanol was then developed to elute the solutes at 55 degrees C within a separation time of 40 min with a minimum resolution of 1.0 for the worst pair. This method was demonstrated to resolve the fatty acids in a vegetable shortening.

Ultraviolet and fluorescence derivatization reagents for carboxylic acids suitable for high performance liquid chromatography: a review

Pre- and postcolumn derivatization with a suitable chromophore or fluorophore have often been utilized to enhance the sensitivity and selectivity of detection for analytes possessing a carboxyl group. The major classes of UV and fluorescent derivatization reagents include the coumarin analogues, alkyl halides, diazoalkanes, and amines. The derivatization reaction conditions, HPLC systems for separation of the conjugates and detection limits of various analytes are presented in this review. High mass sensitivity for various carboxylic acids have been achieved with the hydrazides, anthracenes, and diazoalkanes.

Liquid chromatographic determination of okadaic acid and dinophysistoxin-1 in shellfish after derivatization with 9-chloromethylanthracene

The reagent 9-chloromethylanthracene was evaluated for derivatization of the diarrhetic shellfish poisons, okadaic acid and dinophysistoxin-1 (DTX-1), to form fluorescent products separable by liquid chromatography. The toxins were reacted with the reagent in acetonitrile in the presence of tetramethylammonium hydroxide for 1 h at 90 degrees C. The products were purified by using two silica solid-phase extraction cartridges before being determined by reversed-phase liquid chromatography with fluorescence detection. The results are comparable to those obtained using 9-anthryldiazomethane (ADAM) for okadaic acid and DTX-1 in mussel tissue. Detection limits were estimated to be about 70-100 ng/g hepatopancreas (equivalent to 12-20 ng/g whole tissue) for each toxin.

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.

General strategies and selection of derivatization reactions for liquid chromatography and capillary electrophoresis

The general strategies, reasons and the different possibilities for the derivatization of biomedically important compounds are reviewed. Different approaches apply for small versus large analyte molecules, different advantages and disadvantages are visualized with pre- and post-column arrangements. Particular interest is focused upon solid-phase derivatization reagents.

Highly sensitive determination of imidapril, a new angiotensin I-converting enzyme inhibitor, and its active metabolite in human plasma and urine using high-performance liquid chromatography with fluorescent labelling reagent

A method for the simultaneous determination of imidapril and its active metabolite in human plasma and urine has been developed using high-performance liquid chromatography with a fluorescent labelling reagent, 9-anthryldiazomethane. Imidapril and its active metabolite were extracted from human plasma and urine using a solid-phase extraction cartridge (Bond Elut C18). Two compounds in the eluate were derivatized with 9-anthryldiazomethane and purified with a solid-phase extraction cartridge (Bond Elut SI). The derivatives were analysed using high-performance liquid chromatography with fluorometry. The detection limits of imidapril and its active metabolite were 0.2 ng/ml in plasma and 10 ng/ml in urine. This method could be applied to the pharmacokinetic study of imidapril.

Determination of fatty acids in fish oil dietary supplements by capillary chromatography with laser-induced fluorescence detection

The 4-bromomethyl-7-methoxycoumarin derivatives of 14 saturated and unsaturated fatty acids, including the omega-3 fatty acids, were separated by reversed-phase liquid chromatography and detected by laser-induced fluorescence. Baseline resolution was obtained by using a high-efficiency packed capillary column with 240,000 theoretical plates, together with a systematic optimization of the mobile phase composition. The retention indices of the fatty acid derivatives correlated well with a predictive empirical model, showing accuracy better than 0.46% relative error and reproducibility better than +/- 0.1% relative standard deviation. The physiologically important fatty acids with 12-22 carbon atoms and 0-6 double bonds were determined at the femtomole level in fish oil dietary supplements by using this methodology.

Liquid chromatographic monitoring of pseudocholinesterase activity: comparison of methods

In order to study the activity of pseudocholinesterase in vitro, two liquid chromatographic techniques have been developed. One is based on phase transfer-catalyzed (PTC) esterification of the carboxylic acid formed during hydrolysis of the substrate, and the other on the use of a radioisotopically labeled substrate. In both cases, the substrate used was a long-chain choline ester. The PTC method, utilizing (N-9-acridinyl)bromoacetamide as a fluorogenic labeling reagent in an aqueous-organic two-phase system, gives esters with very high fluorescence intensity. The radiochromatographic method makes use of on-line radioactivity monitoring of the substrate and product in order to follow the hydrolysis reaction. In both methods reversed-phase liquid chromatography is used. A method for the synthesis of 3H-labeled choline esters is also described. Both techniques are compared with regard to sensitivity, reproducibility and practical considerations.

High-performance liquid chromatographic determination of biotin in biological materials after crown ether-catalyzed fluorescence derivatization with panacyl bromide

This paper reports a high-performance liquid chromatographic (HPLC) technique to determine biotin in biological samples. Biotin and the internal standard dethiobiotin are converted into fluorescent derivatives by using panacyl bromide [p-(9-anthroyloxy)phenacyl bromide] as a fluorescence label. Biotin is extracted from biological tissue with trichloroacetic acid and the extract is purified by a combination of solid-phase extraction on C18 cartridges, ion-exchange chromatography on DOWEX formate resin, and thin-layer chromatography. The purified sample extract is derivatized in the presence of a crown ether. The resulting panacyl esters can be separated on reversed-phase as well as on normal-phase HPLC. Normal phase HPLC is preferable because it provides higher sensitivity and demands less sample pretreatment. Analysis of rat intestinal tissue revealed that only about 13% of the biotin is present in free form whereas 87% is bound in proteins from which it can be released by hydrolysis. Biotin values determined by this method are comparable to those obtained by other techniques.

Pre-column derivatization of free bile acids for high-performance liquid chromatographic and gas chromatographic-mass spectrometric analysis

Pentachlorophenyl (PCP) esters of five free bile acids (FBA) were obtained by reacting the FBA and Kovacs' complex (KC) in a 1:8 molar ratio in acetone at 65 degrees C, and were purified by column chromatography on silica gel. The esters were crystallized from benzene-hexane, derivatized as trimethylsilyl ethers for gas chromatography on a DB-1 capillary column and for gas chromatography-mass spectrometry with a DB-5 column, and mass spectrometry (MS) in the electron-impact (EI) positive-ion mode at 70 eV. The reaction is specific for FBA even in the presence of glycine and taurine conjugates of bile acids. The PCP esters were treated with benzylamine in chloroform or methanol to produce N-benzyl derivatives of FBA. The N-benzylamides were separated by high-performance liquid chromatography (HPLC) on a 4-microns Nova-Pak C18 column, studied by thermospray-LC-MS, and in the direct insertion probe-EI positive-ion mode.

N-(9-acridinyl)-bromoacetamide--a powerful reagent for phase-transfer-catalyzed fluorescence labeling of carboxylic acids for liquid chromatography

Phase-transfer-catalyzed esterification of various carboxylic acids has been carried out on a microanalytical scale with a new reagent, N-(9-acridinyl)-bromoacetamide, in aqueous/organic two-phase systems. The procedure gives esters showing very high fluorescence intensity in acid solution. The large Stokes' shift (greater than 120 nm) means that a low background can be achieved even when using a large emission bandwidth. These derivatives show very good chromatographic behavior on reversed-phase liquid chromatographic columns with the use of aqueous acetonitrile, containing 0.2% of phosphoric acid, as the mobile phase. Detection limits (S/N = 2) as low as 10 fmol can be obtained under optimal conditions.

New ultraviolet labelling agents for high-performance liquid chromatographic determination of monocarboxylic acids

New UV-labelling agents have been synthesized, which are designed to convert monocarboxylic acids into their highly UV-absorbing derivatives for enhancement of the sensitivities of UV detection in high-performance liquid chromatography. The reagents are p-nitrobenzyl, 3,5-dinitrobenzyl and 2-(phthalimino)ethyl p-toluenesulphonates. Each has been prepared by reaction of p-toluenesulphonyl chloride with p-nitrobenzyl alcohol, 3,5-dinitrobenzyl alcohol or N-(hydroxyethyl)phtalimide, respectively, in the presence of sodium hydroxide, and they are stable in the solid state for at least 6 months. Monocarboxylic acids were derivatized to their p-nitrobenzyl, 3,5-dinitrobenzyl or 2-(phthalimino)ethyl esters with each of the above reagents, respectively, then determined by high-performance liquid chromatography with UV detection. In the UV-labelling with each reagent, 18-crown-6 was used as the catalyst. The effects of the reaction solvent, reaction temperature and time and the concentrations of each reagent and the catalyst were also examined.

New preparation method for 9-anthryldiazomethane (ADAM) as a fluorescent labeling reagent for fatty acids and derivatives

A preparation method for 9-anthryldiazomethane (ADAM) as a fluorescent labeling reagent for carboxylic acids is described. 9-Anthraldehyde hydrazone is oxidized with an organic oxidant, N-chlorosuccinimide, in an organic solvent such as ethyl acetate to give ADAM, and then the reaction mixture is directly used as the reagent solution for the derivatization of carboxylic acids. Both the oxidation and the derivatization reaction are carried out at room temperature, and an aliquot of the derivatization mixture is directly injected into a chromatograph. 9-Anthrylmethyl ester derivatives formed from ADAM and various carboxylic acids are sufficiently separated on a reversed-phase column and are sensitively detected fluorometrically. The present method was applied to the high-performance liquid chromatographic determination of long and short chain fatty acids, keto acids, and hydroxy acids.

Benzyl esters of C2-C20 fatty acids and metabolically relevant carboxylic acids. Preparation and gas chromatography-mass spectrometry

Short-, medium- and long-chain fatty acids, and other types of metabolically relevant carboxylic acids like hydroxy-, keto-, aromatic and dicarboxylic acids, were analyzed by capillary gas chromatography. For separation, benzyl ester derivatives were used, prepared by reaction of the potassium carboxylates with benzyl bromide in acetonitrile catalyzed by a crown ether. The reaction conditions for quantitative benzylation were studied. Keto groups of ketocarboxylic acids were stabilized prior to benzylation by formation of O-methyl oximes using methoxyamine hydrochloride in aqueous-ethanolic solution. The separation of more than 45 carboxylic acids was achieved on a CP-Sil 5 CB fused-silica capillary column in less than 70 min. The electron impact mass spectra of ketocarboxylic acid O-methyl oxime benzyl esters

Analysis of fatty acids as their anthrylmethyl esters by high-performance liquid chromatography with fluorescence detection

A reversed-phase high-performance liquid chromatographic method for the analysis of free fatty acids in plasma has been developed which allows the resolution of the major plasma fatty acids in man. A mixture of thirteen fatty acid anthrylmethyl esters is resolved on a Spherisorb 3-micron C8 column at a flow-rate of 1 ml/min by gradient elution. The solvent system consists of acetonitrile-water (93:7) for 12 min, followed by 5 min at acetonitrile-water (86:14) and 23 min at 100% acetonitrile. The eluent is monitored with a fluorescence detector (excitation 360 nm, emission 420 nm). Three different C18 columns were evaluated, and none were able to resolve all the esters. To optimize the separation on the C8 columns it was necessary to construct plots of log capacity factor vs. percent water in the mobile phase. The slope of the line for arachidonic acid (C20:4) was markedly different from that for the saturated acid derivatives. The method was applied to the analysis of plasma free fatty acids in normal and diabetic subjects. As expected, elevated levels of free fatty acids were found in diabetic subjects. The results were shown to correlate well with an established gas chromatographic assay.

Improved high-performance liquid chromatographic analysis of some carboxylic acids in food and beverages as their p-nitrobenzyl esters

An improved, straightforward and accurate method for the derivatization and quantitative high-performance liquid chromatographic analysis of carboxylic acids in food and beverages is presented. Thirty-two p-nitrobenzyl esters were prepared in high yields by direct reaction of the free acid with O-(4-nitrobenzyl)-N,N'-diisopropylisourea in dioxane-water (9:1). Benzylmalonic acid was used as a new internal standard. Excess of reagent was removed on a strong cation-exchange resin. The advantage of this original and very convenient procedure over the usual clean-up step involving filtration through a disposable silica cartridge is discussed. The p-nitrobenzyl ester derivatives were readily separated using a single linear gradient of solvent (acetonitrile in water). With a high-performance liquid chromatography column of conventional size (20-25 cm X 4.6 mm I.D.), the analysis lasted for less than 20 min. This analysis time was even shorter (less than 12 min) when using modern small-bore (100 X 2.1 mm I.D.) columns. Applications of the method to the analysis of the main carboxylic acids in coffee, wine and fruit juices are presented.

Separation and quantitation of fatty acids by high-performance liquid chromatography

To facilitate the determination of the fatty acid composition of tissues and the investigation of fatty acid metabolism, we developed a method for the rapid separation by high-performance liquid chromatography and quantitation (by ultraviolet light absorption) of p-bromophenyl esters of fatty acids which vary in chain length from 10 to 22 carbon atoms. The utility of the method was demonstrated by evaluating the fatty acid composition of human uterine decidua vera tissue and human endometrial stromal cells that are maintained in monolayer culture.

A comparison of methods for the high-performance liquid chromatographic and capillary gas-liquid chromatographic analysis of fatty acid esters

A reversed-phase high-performance liquid chromatographic (RP-HPLC) method for the analysis of free fatty acids in plasma was compared with a method using capillary gas-liquid chromatography (GLC). The same extraction procedure was used for both assays. In the RP-HPLC method, the acids were separated as their anthrylmethyl esters on a C18 reversed-phase column, and detected by fluorescence. The coupling agent 2-bromo-1-methylpyridinium iodide was used with 9-(hydroxymethyl)anthracene. A mobile phase of acetonitrile-water (98:2) was used with flow programming. The derivatives of the C14:0, C16:1 and C18:2 acids could not be fully resolved. For capillary GLC, the acids were separated as their methyl esters following on-column injection into a 25-m OV-101 glass capillary column and detected using flame ionization detection. The esterifying agent used was diazomethane. The C18:2 and C18:3 esters were not fully resolved. The precision and sensitivity of both methods were similar. In an application of the methods, the free fatty acid concentrations in the plasma of a group of diabetic patients and their age-matched controls were estimated. Fatty acid concentrations tended to be higher in the diabetic group but, in the small number of patients studied, wide inter-individual variations prevented a significant difference from being detected. Estimates of individual fatty acids were higher by the RP-HPLC method. The identity of the acids in the extract was confirmed by gas chromatography-mass spectrometry of their methyl esters.

Liquid chromatography/mass spectrometry of fatty acids as their anthrylmethyl esters

The mass spectra of a series of saturated and unsaturated fatty acids have been recorded as their anthrylmethyl esters using a liquid chromatographic mass spectrometric interface. The spectra show an intense peak for the aromatic nucleus, and a molecular ion. The liquid chromatographic/mass spectrometric separation was performed on a reverse phase column using a solvent system of acetone + acetonitrile. While a complete separation of the fatty acids known to occur in man was not achieved, the recognition of all of these acids is possible using a scanning mode or by ion monitoring.

High performance liquid chromatographic separation of stereoisomeric bile acids as their UV-sensitive esters

High performance liquid chromatographic separation of a series of mono-, di- and trihydroxylated 5 beta-cholanic acids, which differ only in position and configuration of hydroxyl groups at positions C-3, C-7 and/or C-12, is reported. The C-24 free acids were derivatized to four different classes of UV-sensitive esters, i.e., p-bromophenacyl (BP), m-methoxyphenacyl (MP), 4-nitrophthalimidemethyl (NPM) and 9-anthrylmethyl (AM) esters, and chromatographed on two variants of C18 reversed-phase columns (Nova-Pak C18 and Zorbax ODS) with methanol-water systems as mobile phase. Separation efficiency and elution order of some isomeric pairs were influenced by both the structure of the C-24 ester groups and the nature of the columns used. Excellent chromatographic properties were found for those derivatives, particularly for the NPM esters.

New derivatization reactions in pharmaceutical analysis

The application of chemical reactions in conjunction with spectrometric and chromatographic methods is exemplified by the formation of 2-nitrophenylhydrazide derivatives for the spectrometric assay of carboxylic acids; silylation and trifluoroacetylation of drugs for gas chromatography; selective reduction of steroid ketones for their IR spectrometric identification; the use of epoxidation in discriminating between saturated and unsaturated steroids in gas chromatography; increasing the selectivity and sensitivity of the spectrometric and gas chromatographic determination of isomeric Delta4- and Delta5-3-ethylenedioxy steroids by treatment with hydrochloric acid; and the use of the same reagent in the difference spectrometric determination of 2,5-dimethyl-alpha-ethyl benzhydrol.