Carboxylic Acid Analytes

One major class of analytes that has been studied repeatedly over the years is that of the fatty acids. They are conveniently separated into three classes short-chain ( C 2 chain lengths), long-chain (C12-C24), and very long-chain ( 24). 

and trichloroacetic acid and mono- and dibromoacetic acid levels were monitored in water [273]. Separation was generated on a C g column 

Pour annatto compounds (natural color conqioundsX a- and /l-bixin and a- and fi-norbixin, were extracted from high-fat daily products and resolved on a C g column X = 500 nm). Peaks were unresolved and extremely fronted when a 100% methanol mobile phase was used [277], However, the use of a 90/10 methanol/water (2% acetic acid) mobile phase produced good peak shape and excellent resolution. The addition of acetic acid obviously kept the analytes frilly protonated, therelqr generating symmetric peak shape. The analysis was complete in lOmin. Detection limits of 5ng/g and calibration ranges up to 450pg/g were reported for the all analytes. 

Eleven chlorogenic acids (e.g., p-coumaroylquinic acids, caffeoylquinlc acids, feruloylquinic acids) were extracted fiom coffee and analyzed on a Cjg column 

Ribotta et al. [281] studied a series of six catecholamine metabolites (vanilman-delic acid, homovanillic acid, 3,4-dihydroxymandelic acid, 3,4-dihydroxy- and 4-hydroxy-3-methoxyphenylacetic acid, vanillic acid). They were well resolved on a C g column (electrochemical detector, 0.75 V). A 15/85 methanol/water (2mM tetrabutylammonium bromide at pH 4.5) mobile phase eluted all compounds in 10 min. A linear range of 3 x 10 to 5 x 10 M and detection limits of 2 x 10 (S/N = 3) were reported. A considerable amount of supportive data such as retention time vs. pH, % methanol, and tetrabutylammonium bromide concentration is also given. Also, detector response versus potential from 0.3 to 0.8 V is shown. 

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The tendency of carboxylic acid analytes to form associative multimers can also be viewed as multilayer adsorption. Analysis of the concentration profiles presented in Fig. 2 reveals that for low concentrations of the analyte, peaks a and b are similar to the band profiles simulated by use of the Langmuir isotherm, whereas peaks c-f resemble profiles obtained by use of the anti-Langmuir isotherm (tailing toward the front of the chromatogram is more pronounced than tailing toward the start of the chromatogram.). 

Boronic acid-derived fluorescent chemosensors are unique in that the inter-molecular interaction is a covalent bond, and not hydrogen bonding as is the case for most conventional fluorescent molecular sensors used for the selective reeognition of hydroxyl carboxylic acids. This chapter summarizes the development of the boronic acid-based chiral fluorescent chemosensors over recent years and the enantioselective fluorescent reeognition of chiral a-hydroxyl carboxylic acids analytes in aqueous solutions. The fundamental scaffolds of these chiral sensors include a fluorophore, an arylboronie aeid binding site, and linker between the two units. The systems usually consist of a bis-boronic acid unit, which is required for enantioselective recognition of the chiral a-hydroxyl carboxylic acid analytes. However, mono-boronic acid fluorescent chemosensors have also been developed. All three components of the chiral boronic acid sensors play an important role in determining the... 

In the case of carboxylic acids, analytical procedures are quite different due to their ionic character. Ion chromatography is the method of choice for more volatile carboxyhc acids and data are regularly included with inorganic analysis of major ions such as phosphate and sulphate [65,66]. Formic, acetic and propionic acids are most commonly reported. Recent studies have only been carried out in air. Concentrations in snow were most recently reported by Kippenberger and co-workers [67], who used a liquid chromatography method with time of flight mass spectrometric detection on snow samples from the Fee glacier in Switzerland (at altitudes from 3,056 to 3,580 m asl). The authors also provided older comparison data from remote and urban sites [68-70],... 

Claisen ester condensation, 6, 279 Thiazolecarboxylic acid chlorides reactions, 6, 279-280 Thiazolecarboxylic acid hydrazides synthesis, 6, 280 Thiazolecarboxylic acids acidity, 6, 279 decarboxylation, 6, 279 reactions, S, 92 6, 274 Thiazole-2-carboxylic acids decarboxylation, S, 92 Thiazole-4-carboxylic acids stability, S, 92 Thiazole-5-carboxylic acids decarboxylation, S, 92 Thiazole-4,5-dicarboxylic acid, 2-amino-diethyl ester reduction, 6, 279 Thiazole-4,5-dicarboxylic acids diethyl ester saponification, 6, 279 Thiazolediones diazo coupling, 5, 59 Thiazoles, 6, 235-331 ab initio calculations, 6, 236 acidity, S, 49 acylation, 6, 256 alkylation, S, 58, 73 6, 253, 256 analytical uses, 6, 328 antifogging agents... 

Acylation of various oxygen functions by use of common and commercially available fluonnated carboxylic acid denvatives such as trifluoroacetic anhydride or the corresponding acyl halides have already been discussed sufficiently in the first edition [10] Therefore only exceptional observations will be described in this section In the past 15 years, many denvatizations of various nonfluonnated oxygen compounds by fluoroacylation were made for analytical purposes. Thus Mosher s acid chlorides for example became ready-to-use reagents for the determination of the enantiomeric purity of alcohols and amines by NMR or gas-liquid chromatographic (GLC) techniques [//] (equation 1)... 

It is well known that pMMA and pSty in THF follow ideal GPC behavior on many common GPC columns. However, many commercially important acrylate polymers contain a wide array of other monomers. In general, acrylic polymers composed of monomers that do not contain polar groups will yield well-behaved polymers, giving ideal GPC separations. Monomers that contain polar groups should prompt the analyst to carefully evaluate the possibility of adsorption of the analyte onto the column. The most common functionalities of concern are hydroxyl groups, amine groups, ethylene oxide units, and carboxylic acids. In many cases, such monomers can be tolerated. However, the acceptable level can vary considerably with even apparently minor changes in... 

A mixture of 26 parts of 3-carbethoxy-6,7-methylenedioxy-4-hydroxy-quinoline, 16 parts of sodium hydroxide and 50 parts of dimethylformamide is heated at 70° to 75°C for 2 hours, then 31 parts of ethyl iodide is added over 1 hour with continued heating and stirring. After an additional 3 to 4 hours of heating (at 70° to 75°C) and stirring, the mixture is diluted with 500 parts of water, refluxed for 3 to 4 hours, acidified with concentrated hydrochloric acid and filtered to yield 18 to 22 parts of 1-ethyl-1,4-dihydro-6,7-methylene-dioxy-4-oxo-3-quinoline-carboxylic acid, MP 309° to 314°C (decomposes). The analytical sample from dimethylformamide melts at 314° to 316°C (decomposes). 

The analytical method described is also used in following the consumption of peroxybenzoic acid or other peroxy acids during an oxidation reaction it has also been used in determining the conversion of other carboxylic acids to peroxy acids when solvent extraction has been used in the isolation. 

In comparison with other anionics, little has been published concerning methods of analysis of ether carboxylates. Gerhardt et al. [238] investigated the analytical determination of ether carboxylic acids in reaction mixtures obtained by reaction of nonylphenol ethoxylates with sodium chloroacetate as well as by cyanoethylation by different methods. Several methods, used for other surfactants as well [239], can be used for ether carboxylates. 

Then, the examples from Reference 23, that focus on retention of the selected binary mixtures of the test analytes (one comprising carboxylic acid and ketone and the other made of alcohol and ketone), chromatographed under the deliberately mild working conditions (microcrystalline cellulose was used as adsorbent and either decalin or n-octane as the monocomponent mobile phase) will be discussed. One of the test solutes in each binary mixture (either acid or alcohol) can be viewed as... 

In the ease of very immatnre organie matter, or when the main research aim is to investigate polar fractions, a different analytical scheme may be applied (Figure 15.3). Prior to the fractionation, total concentrated extracts are treated with 14% BF3 in methanol or diazomethane in ether to esterify free carboxylic acids, and then they are snbjected to silica gel TLC using methylene chloride or a mixture of... 

The scope of the multi-residue method is extended permanently by testing and then including further active substances that can be determined by GC. Acidic analytes (such as phenoxyacetic acids or RCOOH metabolites) are included into the homogeneous partitioning by acidifying the raw extracts to a pH below the pKs value of the carboxylic acids. To include these analytes in the GC determination scheme they have to be derivatized with diazomethane, diazoethane, trimethylsilyldiazomethane, acidic esterification or benzylation, or by silanizing the COOH moiety. 

At this point, the anaiyte may not be amenabie to UV, FL, or EC detection. In this case, the best course of action may be to choose LC/MS (see Section 4.2). However, one other option is to use a pre- " or post-coiumn derivatization step to increase the detectabiiity of the anaiyte with respect to FL or UV. Fluorescent or UV labels are available for carboxylic acids," amines, phenols, and thiols. The decision to use pre- or post-column derivatization is predicated upon the functionality of the analyte available for derivatization and the rate and extent of the reaction between each derivatizing agent and the analyte. 

A. Yagi, K. Mizuno, Y. Asano, and K. Ishikawa, Residue analytical method for the calcium salt of 3,5-dioxo-4-propionylcyclohexane-l-carboxylic acid (prohexadione-calcium) in crops, in Abstracts of the 16th Annual Meeting of the Pesticide Science Society of Japan, p. 114 (1991). 

Figure 9 A synthetic mixture of water-soluble carboxylic acids separated by anion-exchange chromatography. Column 0.3 cm x 300 cm Diaoion CA 08, 16-20 p (Mitsubishi Kasei Kogyo). Eluant 200 mM HC1. Detection reaction with Fe3-benzohy-droxamic acid-dicyclohexy carbodiimide-hydroxylamine perchlorate-triethyl amine with absorbance at 536 nm. Analytes (1) aspartate, (2) gluconate, (3) glucuronate, (4) pyroglutamate, (5) lactate, (6) acetate, (7) tartrate, (8) malate, (9) citrate, (10) succinate, (11) isocitrate, (12) w-butyrate, (13) a-ketoglutarate. (Reprinted with permission from Kasai, Y., Tanimura, T., and Tamura, Z., Anal. Chem., 49, 655, 1977. 1977 Analytical Chemistry).

Biological and Analytical Applications. - Phosphorus-31 n.m.r. continues to expand its application in the medical and biological fields20 and is now being applied to soil analysis.21 The problems involved in the use of FT 31P n.m.r. for quantitative determinations have been discussed.22 Samples of phosphinic carboxylic acids were cooled to -40°Cfor quantitative estimations.23... 

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