Determination Of Carboxylic Acids Research Articles

The Use of Piezosensors for Determination of Carboxylic Acids in the Intermediate Products of Edible Ethanol Production

The reference polymers and polymers with molecular imprints of carboxylic acids (MIPs-CA)—propionic (MIP-Propionic) and butyric (MIP-Butyric) acids—were synthesized on the surface of piezoelectric sensors using aromatic compounds by the non-covalent imprinting method. A molecularly imprinted polymer (MIP) is a polymer produced through molecular imprinting, which leaves cavities in the polymer matrix with affinity for a chosen “template” target molecule. The values of the imprinting factor and selectivity coefficients were calculated to assess the ability of MIPs-CA to recognize the target molecules. It was shown that the sensors modified by the molecularly imprinted polymers exhibited high selectivity for the acid that was a template during their synthesis. The detection limits for propionic and butyric acids were 7.40 × 10–6 and 8.81 × 10–6 g/dm3, respectively. Correctness of the carboxylic acid determination in model solutions was verified in the spike/recovery tests. The relative standard deviation was less than 10%. The modified piezoelectric sensors were tested in analysis of the intermediate products of edible ethanol production (distillate of fermentation mixture, epurate, bottom liquids of columns). The correctness of the determination of carboxylic acids in liquids was evaluated using an Agilent Technologies 7890B GC System. The difference in the results of acid determination between both methods (piezoelectric sensor and chromatography–mass spectrometry) did not exceed 6%. The modified piezosensors expand the potential of rapid determination of carboxylic acids in the intermediate products of ethyl alcohol production.

Improving liquid chromatography-tandem mass spectrometry determination of polycarboxylic acids in human urine by chemical derivatization. Comparison of o-benzyl hydroxylamine and 2-picolyl amine

Due to its high sensitivity and specificity, liquid chromatography-electrospray tandem mass spectrometry (LC–MS/MS) could be considered as the gold-standard in targeted metabolomics. Although LC–MS/MS allows for the direct detection of a large number of molecules, the proper quantification of highly polar compounds such as poly-carboxylic acids in complex matrices like urine is still a challenge. Chemical derivatization offers a suitable way to improve chromatographic behavior and sensitivity for these compounds. Several derivatizing agents have been proposed for the LC–MS/MS determination of carboxylic acids but studies dealing with their comparison in challenging scenarios are scarce. Here we present the evaluation of two different derivatization agents; o-benzylhydroxyl amine (oBHA) and 2-picolyl amine (2-PA); for the quantification of the (poly)-carboxylic acids belonging to the tricarboxylic acid cycle in urine. The suitability of both derivatizating agents was compared by validation of the two approaches. Derivatization with oBHA showed important advantages against 2-PA derivatization such as (i) providing better sensitivity, (ii) more stable derivatives and (iii) allowing for the proper validation of a larger number of analytes. Moreover, while 2-PA derivatization failed in the determination of the target analytes in some stored urine samples, oBHA derivatization successfully allowed for their appropriate determination in the same samples. A comparison between the concentrations obtained using oBHA derivatization and those provided by an external laboratory using UV and GC–MS detection revealed a satisfactory agreement between both results. Additionally, the concentrations obtained by the oBHA method for a set of 38 urines are in agreement with those previously reported in the literature. As a conclusion, our results show that the use of oBHA is preferred against 2-PA for the detection and quantification of (poly)-carboxylic acids in urine.

Determination of carboxylic acids in non-alcoholic beer samples by an ultrasonic-assisted dispersive micro-solid phase extraction based on Ni/Cu-Al layered double hydroxide nanocomposites followed by gas chromatography

Magnetically separable layered double hydroxide Ni/CuAl-LDH nanocomposites were synthesized and employed as ultrasonic-assisted dispersive micro-solid phase extraction (UA-D-μSPE) sorbent to extract several carboxylic acids (namely propionic, butyric, pentanoic, hexanoic, heptanoic, octanoic, and decanoic) from non-alcoholic beer samples. Ni/CuAl-LDH sorbent was characterized by Fourier transform-infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). Effective variables such as amount of sorbent (mg), pH and ionic strength of sample solution, volume of eluent solvent (μL), vortex, and ultrasonic times (min) were investigated via fractional factorial design (FFD). The significant variables were optimized by a Box–Behnken design and combined by a desirability function (DF). Under optimized conditions, the calibration graphs of analytes were linear in a concentration range of 0.05–100μg/mL and had correlation coefficients more than 0.997. The limits of detection and quantification were in the ranges of 16–40μg/L and 53–133μg/L, respectively. This procedure was successfully employed in the determination of target analytes in spiked beer samples, and the relative mean recoveries ranged from 87 to 110%.

Application of a Fluorescent Derivatization Reagent 9-Chloromethyl Anthracene on Determination of Carboxylic Acids by HPLC

A simple and sensitive high-performance liquid chromatography (HPLC) method is proposed for the analysis of some carboxylic acids in food samples and the environment. The use of 9-chloromethyl anthracene as a fluorescence-labeling reagent has been investigated. The derivatization reagent reacts with unitary carboxylic acids and tetrabutylammonium bromide as a catalyst within 50 min in acetonitrile to give esters, which can be separated by HPLC employing fluorescence detection at λ(ex) = 365 and λ(em) = 410 nm. The optimum conditions for derivatization, fluorescence detection and chromatographic separation are established. The method shows good sensitivity, with a detection limit from 0.18 to 2.53 pmol, and good linearity between 1-250 nmol/mL of each analyte. The practical applicability of the method was demonstrated by analyzing samples that were spiked with the acid standards, environment and food samples.

Determination of carboxylic acids in water by gas chromatography–mass spectrometry after continuous extraction and derivatisation

This paper describes a new approach for the determination of monocarboxylic, dicarboxylic and tricarboxylic acids (35 compounds) in water. The analytes, in acid medium (pH ∼1.3), were sorbed on an 80mg LiChrolut EN–Supelclean ENVI-18 (1:1) column and subsequently eluted with methanol. After evaporation of the extract to ∼10μL, the analytes were spiked with 60μL of the derivatising reagent and derivatised in a household microwave oven for 3min. Among the reagents tested (BF3/1-butanol; acetyl chloride/1-butanol; isobutyl chloroformate/1-butanol; trimethylphenylammonium hydroxide, N,O-bis-(trimethylsilyl)acetamide, N,O-bis-(trimethylsilyl)trifluoroacetamide and trimethylchlorosilane), the best results in terms of reaction yield and stability of the derivatives were obtained with the mixture of 1% trimethylchlorosilane in N,O-bis-(trimethylsilyl)trifluoroacetamide. Microwave assisted derivatisation was used as an alternative heating approach for the rapid silylation of carboxylic acids. The proposed method proved to be a suitable analytical procedure for several types of carboxylic acids in water, with limits of detection within the range 0.6–15ngL−1, precision values from 4.0 to 6.0% (as within-day relative standard deviation) and recoveries from 93 to 101% for all the target analytes.

Identification and determination of carboxylic acids in food samples using 2-(2-(anthracen-10-yl)-1 H-phenanthro[9,10- d]imidazol-1-yl)ethyl 4-methylbenzenesulfonate (APIETS) as labeling reagent by HPLC with FLD and APCI/MS

A new labeling reagent for carboxylic acids, 2-(2-(anthracen-10-yl)-1 H-phenanthro[9,10- d]imidazol-1-yl)ethyl 4-methylbenzenesulfonate (APIETS) has been designed and synthesized. It was used to label eight fatty acids (lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, oleic acid, linoleic acid and linolenic acid) and four hydroxy pentacyclic triterpene acids (oleanolic acid, ursolic acid, betulinic acid and maslinic acid), successfully. APIETS could easily and quickly label carboxylic acids in the presence of K 2CO 3 catalyst at 85 °C for 35 min in N, N-dimethylformamide solvent. The carboxylic acids derivatives were separated on a C 8 reversed-phase column with gradient elution and fluorescence detection at λ ex/ λ em = 315/435 nm. Identification of these derivatives was carried out by online mass spectrometry with atmospheric pressure chemical ionization in positive ion mode. The detection limits obtained were 13.37–30.26 fmol (signal-to-noise ratio of 3). The proposed method has been applied to the quantification of carboxylic acids in sultana raisin (Thompson seedless), hawthorn flake (Crataegus pinnatifida Bge.), Lycium barbarum seed oil and Microula sikkimensis seed oil with recoveries over 95.3%. It has been demonstrated that APIETS is a prominent labeling reagent for determining carboxylic acids with high performance liquid chromatography.

Determination of carboxylic acids in water by gas chromatography using several detectors after flow preconcentration

A novel analytical method is reported that combines continuous solid-phase extraction and gas chromatography for the determination of 22 carboxylic acids in water. The highly polar and hydrophilic analytes were preferentially sorbed on a mixture of LiChrolut EN–Supelclean ENVI-18 (1:1) sorbent column and eluted with methanol; this extraction process did not require derivatisation. The extract was analysed by gas chromatography coupled to a flame ionisation detector as well as a mass spectrometer with electron impact (EI) or positive chemical ionisation modes. The highest sensitivity was achieved when using MS-EI, with good linearity in calibration curves and low detection limits (2–40 ng L −1) for 50 mL of sample. The entire procedure from raw aqueous sample to a ready-to-inject methanol solution of the acids requires less than 15 min. Another benefit of this method is the good accuracy (recoveries between 93 and 102%) and precision (relative standard deviation, 3.4–6.2%), which allows the determination of carboxylic acids in environmental water and in real chlorinated and ozonated drinking water.

ChemInform Abstract: Determination of Carboxylic Acids in the Fruits of Laurocerasus officinalis Roem. and Its Cultivars.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Biosensor for determination of carboxylic acids in wines based on the inhibition of sarcosine oxidase

The flow-through amperometric biosensor is presented for determination of carboxylic acids. It is based on two sensor layers that are deposited on a platinum electrode. The inner layer serves to eliminate interferences by limiting diffusion of electrochemically active substances such as ascorbic acid. This layer is electro-polymerized using an equimolar mixture of o-phenylenediamine and resorcinol. The outer layer is prepared by cross-linking the enzyme sarcosine oxidase and bovine serum albumin using glutaraldehyde. The formation of enzymatically produced hydrogen peroxide is monitored at 600 mV vs. an Ag/AgCl reference electrode. The addition of carboxylic acids causes competitive inhibition of the enzyme and a decrease in signal. The assay was optimized for determination of carboxylic acids in wine samples. Following 10-fold dilution, most samples contain 1–10 mM individual carboxylic acids and thus a 5 mM concentration of sarcosine was chosen as being optimal for competition. In case of real samples, the biosensor measures the sum of all carboxylic acids, which serves as a parameter describing the quality of wines. Results from testing several wine samples are reported.

Capillary electrophoresis for the monitoring of carboxylic acid production by Gluconobacter oxydans

Determination of carboxylic acids in Gluconobacter oxydans fermentations of wheat straw hydrolyzate was carried out. This matrix is of complex composition containing carbohydrates, organic compounds (e.g., amino acids, toxins), and inorganic salts making the analysis challenging even with separation techniques. A method based on capillary electrophoresis with indirect UV detection was developed for the simultaneous quantification of 18 carboxylic acids. The background electrolyte solution of ammonia, 2,3-pyridinedicarboxylic acid, and Ca 2+ and Mg 2+ salts, containing myristyltrimethylammonium hydroxide as a dynamic capillary coating reagent, was validated for the robust and repeatable separation of the carboxylic acids. Intraday relative standard deviations in the optimized method were less than 1.6% for migration times and between 1.0% and 5.9% for peak area. Interday relative standard deviations were less than 5.0% for migration times and between 5.7% and 9.3% for peak area. With 11 nl injected, detection limits for the analytes were between 10 and 43 μmol/l. Detection limits ranged from 0.1 to 0.5 pmol at signal-to-noise ratio of 3. The results demonstrated that wheat straw hydrolyzate was a suitable substrate for G. oxydans with a product yield of 45% for the formation of xylonic acid from xylose and 96% for the formation of gluconic acid from glucose.

Determination of Carboxylic Acids from Plant Root Exudates by Ion Exclusion Chromatography with ESI-MS

Ion-exclusion chromatography (IEC) coupled with electrospray ionization quadrupole mass spectrometry (ESI-MS) has been used for the analysis of carboxylic acids. The use of ESI-MS provides increased specificity and sensitivity compared to existing detection methods. This paper applies IEC-ESI-MS to the analysis of carboxylic acids in commonly found root exudates and shows that the separation of nine carboxylic acids (pyruvic, oxalic, lactic, malonic, maleic, succinic, tartaric, aconitic and citric acids) can be achieved by IEC within 8 min. The ESI provided reasonable signals from negative ions, [M−H]− in the negative ionization mode. Linear plots of peak area versus concentration were obtained in the range 50–25,000 μg L−1 for MS detection under optimized MS conditions. The detection limits of target organic acids, based upon signal to noise ratio (S/N = 3), ranged from 10 to 30 μg L−1. The reproducibility of peak areas was <2.5% (n = 5). The proposed method was used for the confirmation and quantification of carboxylic acids in nutrient solutions containing root exudates.

Confirmation and determination of carboxylic acids in root exudates using LC–ESI‐MS

Reversed-phase liquid chromatography with UV detection is of limited applicability in the separation and identification of carboxylic acids because of the column's poor separation efficiency and the non-selective nature of the UV detector. To address this issue, RP-LC with electrospray ionization mass spectrometry has been explored for the confirmation and determination of carboxylic acids in plant root exudates, with ESI-MS providing structural information, high selectivity, and high sensitivity. The separation of 10 carboxylic acids (pyruvic, lactic, malonic, maleic, fumaric, succinic, malic, tartaric, trans-aconitic, and citric acid) was performed on a C(18) column using an eluent containing 0.1% (v/v) acetic acid within 10 min, where the acidic eluent not only suppressed the ionization of the carboxylic acids to be retained on the column, but was also compatible with ESI-MS detection. In addition, an additional standard was used to overcome the matrix effect. The results showed that peak areas correlated linearly with the concentration of carboxylic acids over the range 0.05-10 mg/L. The detection limits of target acids (signal-to-noise S/N ratio of 3) ranged from 20 to 30 microg/L. Finally, the proposed method was used for the confirmation and determination of low-molecular-weight carboxylic acids in plant root exudates, and provided a simple analytical procedure, including sample processing, fast separation, and high specificity and sensitivity.

1‐Pyrenemethanol, a Useful Fluorometric Reagent for the Detection and Determination of Carboxylic Acids in Atmospheric Samples

A rapid fluorometric procedure for the selective and sensitive determination of carboxylic acids, based on pre‐column derivatization using 1‐pyrenemethanol, was optimized and applied to atmospheric sampling. The optimum conditions for derivatization were determined to be: reaction solvent–dichloromethane, temperature −44°C, reaction time −30 min, and reagent/total acid ratio −15. Separation of the derivatives of acids up to twenty carbons by reversed‐phase (C8) chromatography was achieved in 25 min using a water/acetonitrile gradient with a limit of detection for the derivatives of 20 pg for a 20 µL injection. A scanning detector with good spectral resolution allows qualitative identification of the components in complex samples. When used in atmospheric analysis, the recoveries of carboxylic acids from spiked samples were >80% with repeatabilities below 10% RSD. Low molecular weight acids were encountered predominantly in the vapor phase (0.20 to 92 ng/m3), whereas higher molecular weight acids were found mostly in particulate form (0.15–129 ng/m3).

Determination of Carboxylic Acids in Apple Juice by RP HPLC

Low molecular weight organic acids are most predominant in apple juice among these components fumaric acid was not exceed more than 5 ppm. It was thought that the HPLC is the best method of the determination of organic acids in the apple juice. In this study, chromatographic separation of organic acids of apple juice was obtained by preparing a sample and by applying them to acid phase for extraction and various organic acids content of apple juice, fumaric acid, oxalic acid, tartaric acid and shikimic acids were commented as qualitative and quantitative, too.The organic acids, of which the chromatographic separations were examined, were the acids of fumaric acid, oxalic acid, tartaric acid, ascorbic acid, lactic acid, malic acid, succinic acid and shikimic acid. For this separation, the suitable value are determined by regulating the pH of mobile phase with phosphoric acid in range of pKa ±1.5 (This is the space in which the capacity factors are effectively changed). The concentration of juice was distilled to 11.2 Brix and same pH was applied to cartridge by adjusting with the phosphate buffer at 8.00, and the cartridge was washed with the same buffer and the phase was combined with the first eluant. A suitable distilled percentage of samples were injected and injection volume were determined. In this study, the cartridges of Supelco C18 and Waters C18 were used, datas obtained by both types of cartridges were compared. In this study, the methods of external calibration and added method of standards were applied and slopes were compared.

Isotachophoretic determination of carboxylic acids in biodegradation samples

In the current study a method of isotachophoretic separation of selected carboxylic acids was developed. The method was used for the determination of carboxylated oligo(ethylene glycol)s and their degradation products in biodegradation tests of PEG 250 DA [a mixture of dicarboxylated oligo(ethylene glycol)s]. Two tests were performed in the studies: the Organization for Economic Cooperation and Development (OECD) screening test and the river water die-away test. Both the biodegradation tests proved relatively fast biodegradation of the studied compounds. In the OECD screening test the biodegradation was faster than in the river water die-away test which can be ascribed to a higher concentration of bacteria in the biodegradation liquor. The minimal sample pretreatment and relatively low cost of analysis by the isotachophoretic method used here make it a good alternative to existing methods of carboxylic acids analysis.

Novel stable fluorophore, 6-methoxy-4-quinolone, with strong fluorescence in wide pH range of aqueous media, and its application as a fluorescent labeling reagent

6-Methoxy-4-quinolone (6-MOQ, 1), an oxidation product derived from 5-methoxyindole-3-acetic acid, is a novel fluorophore, which has several useful characteristics for biomedical analysis. Compound 1 has strong fluorescence with a large Stokes’ shift in aqueous media, and the maximum fluorescence excitation and emission wavelengths are 243nm and 374nm, respectively. The molar absorptivity at the maximum excitation wavelength and fluorescence quantum yield in aqueous 10% (v/v) methanol are 32600Lmol−1cm−1 and 0.38, respectively. The fluorescence intensity of 1 is scarcely affected by changing the medium pH, showing strong fluorescence from pH 2.0 to 11.0. In addition, 1 is highly stable against light and heat, and no degradation was observed at 60°C for 3 days with exposure to daylight. As a fluorescent labeling reagent, [(6-methoxy-4-oxo-1,4-dihydroquinolin-3-yl)methyl]amine (6-MOQ-NH2, 2) was synthesized, and determination of carboxylic acids was demonstrated; 50pmol of standard propionic acid and isobutyric acid were derivatized, and the obtained S/N ratios for 10fmol (injection amount) of these two acids were 206 and 164, respectively.

Determination of acid and hydroxyl end-groups in endfunctionalized polystyrenes using 19F NMR

Abstract Carboxyl-terminated polystyrene was esterified with 2,2,2-trifluoroethanol using a carbodiimide-mediated room temperature reaction, and hydroxyl-terminated polystyrene was fluoro-derivatized with trifluoroacetic anhydride. The soformed fluorine-containing esters were then quantitatively determined with 19F NMR, using α,α,α-trifluorotoluene as secondary standard. This provides a technique for the reliable determination of carboxylic acid and hydroxyl groups in small samples of polymers.

Determination of carboxylic acids in wines by liquid ion-exclusion chromatography

Chromatographic behavior of aromatic and aliphatic acids was studied using an ion-exclusive column. Conditions were determined, under which the separation of the acids by single-column ion-exclusion chromatography with UV-detection was the most selective and efficient. The method developed by us was employed for determining the content of carboxylic acids in wines.

Determination of carboxylic acids, carbohydrates, glycerol, ethanol, and 5-HMF in beer by high-performance liquid chromatography and UV-refractive index double detection.

A high-performance liquid chromatographic method is proposed for the simultaneous separation of main carboxylic acids, carbohydrates, ethanol, glycerol, and 5-HMF in beer by direct injection. A column packed with a sulfonated divinyl benzene-styrene copolymer and an isocratic elution with 0.0045N sulfuric acid and acetonitrile (6%, v/v) are employed. UV and refractive index detectors connected in series are also used to reduce the matrix interference of phenolic compounds. In conditions described, nine compounds are quantitated in a single chromatographic run without any pretreatment except for sample dilution and filtration before injection. Precision, accuracy, linearity of response, limit of detection, and limit of quantitation are also evaluated for each compound. Satisfactory results are obtained to justify the application of this method to all phases of beer production for process and quality control.

Influence of organic solvents in the mobile phase on the determination of carboxylic acids and inorganic anions in grape juice by ion chromatography

Investigations have been initiated to develop a sufficiently good separation of both major and minor organic acids and inorganic anions present in grape musts using a Dionex As11 column, a sodium hydroxide gradient elution and a suppressed conductivity detection. Separation was complicated in aqueous mobile phase by co-elutions and selectivity was optimized using organic modifiers that alter ion-exchange selectivity for hydrophobic ions. In this study, the influence of three different solvents (methanol, ethanol and acetonitrile) on the efficiency of column was compared. The best separation of all ions in a synthetic solution was achieved with an eluent containing 13% (v/v) methanol and 13% (v/v) ethanol in water, the run during only 20 min. This method was next applied to grape juices with success and has shown sensitivity and reproducibility. Moreover, sample preparation was a simple 20-fold dilution with 0.45 μm filtration and direct injection without prior sample clean-up.