Microwave-assisted preparation of sugars and organic acids for simultaneous determination in citric fruits by gas chromatography

Determination of organic acids for predicting sourness intensity of tea beverage by liquid chromatography-tandem mass spectrometry and chemometrics methods

The contents of organic acids (OAs) in tea beverage and their relationship with taste intensity have not been fully understood. In this work, a rapid (10 min for a single run) and sensitive (limits of quantification: 0.0044-0.4486 µg/mL) method was developed and validated for the simultaneous determination of 17 OAs in four types of tea, based on liquid chromatography-tandem mass spectrometry with multiple reaction monitoring mode. The contents of 17 OAs in 96 tea samples were measured at levels between 0.01 and 11.80 g/kg (dried weight). Quinic acid, citric acid, and malic acid were determined as the major OAs in green, black, and raw pu-erh teas, while oxalic acid and tartaric acid exhibited the highest contents in ripe pu-erh tea. Taking the OAs composition as input features, a partial least squares regression model was proposed to predict the sourness intensity of tea beverages. The model achieved a root-mean-square error of 0.58 and a coefficient of determination of 0.84 for the testing set. The proposed model provides a theoretical way to evaluate the sensory quality of tea infusion based on its chemical composition.

Ion-Exclusion High-Performance Liquid Chromatography of Aliphatic Organic Acids Using a Surfactant-Modified C18 Column

Ion exclusion chromatography (IELC) of short chain aliphatic carboxylic acids is normally done using a cation exchange column under standard HPLC conditions but not in the ultra-HPLC (UHPLC) mode. A novel IELC method for the separation of this class of carboxylic acids by either HPLC or UHPLC utilizing a C18 column dynamically modified with sodium dodecyl sulfate has been developed. The sample capacity is estimated to be near 10 mM for a 20 µL injection or 0.2 µmol using a 150 × 4.6 mm column. The optimum mobile phase determined for three standard mixtures of organic acids is 1.84 mM sulfuric acid at pH 2.43 and a flow rate of 0.6 mL/min. Under optimized conditions, a HPLC separation of four aliphatic carboxylic acids such as tartaric, malonic, lactic and acetic can be achieved in under 4 min and in <2 min in the UHPLC mode at 2.1 mL/min. A variety of fruit juice and soft drink samples are analyzed. Stability of the column as measured by the retention order of maleic and fumaric acid is estimated to be ∼4,000 column volumes using HPLC and 600 by UHPLC. Reproducible chromatograms are achieved over at least a 2-month period. This study shows that the utility of a C18 column can be easily extended when needed to IELC under either standard or UHPLC conditions.

Rapid determination of main constituents of packed juices by reverse phase-high performance liquid chromatography: an insight in to commercial fruit drinks

The present work reports the compositional analysis of thirteen different packed fruit juices using high performance liquid chromatography (HPLC). Vitamin C, organic acids (citric and malic) and sugars (fructose, glucose and sucrose) were separated, analyzed and quantified using different reverse phase methods. A new rapid reverse phase HPLC method was developed for routine analysis of vitamin C in fruit juices. The precision results of the methods showed that the relative standard deviations of the repeatability and reproducibility were <0.05 and <0.1 respectively. Correlation coefficient of the calibration models developed was found to be higher than 0.99 in each case. It has been found that the content of Vitamin C was less variable amongst different varieties involved in the study. It is also observed that in comparison to fresh juices, the packed juices contain lesser amounts of vitamin C. Citric acid was found as the major organic acids present in packed juices while maximum portion of sugars was of sucrose. Comparison of the amount of vitamin C, organic acids and sugars in same fruit juice of different commercial brands is also reported.

Determination of carbohydrates in medicinal plants--comparison between TLC, mf-MELDI-MS and GC-MS

INTRODUCTION

Quality control in the pharmaceutical and phytopharmaceutical industries requires fast and reliable methods for the analysis of raw materials and final products.

OBJECTIVE

This study evaluates different analytical approaches in order to recognise the most suitable technique for the analysis of carbohydrates in herbal drug preparations.

METHODOLOGY

The specific focus of the study is on thin-layer chromatography (TLC), gas chromatography (GC), and a newly developed mass spectrometric method, i.e. matrix free material enhanced laser desorption/ionisation time of flight mass spectrometry (mf-MELDI-MS). Samples employed in the study were standards and microwave-assisted water extracts from Quercus.

RESULTS

TLC analysis proved the presence of mono-, di- and trisaccharides within the biological sample and hinted at the existence of an unknown carbohydrate of higher oligomerisation degree. After evaluation of different derivatisation techniques, GC-MS confirmed data obtained via TLC for mono- to trisaccharides, delivering additionally quantified values under a considerable amount of time. A carbohydrate of higher oligomerisation degree could not be found. The application of mf-MELDI-MS further confirmed the presence of carbohydrates up to trisaccharides, also hinting at the presence of a form of tetrasaccharide. Besides this information, mf-MELDI-MS delivered further data about other substances present in the extract. Quantitative determination resulted in 1.750, 1.736 and 0.336 mg/mL for glucose, sucrose and raffinose respectively.

CONCLUSION

Evaluation of all three techniques employed, clearly proved the heightened performance of mf-MELDI-MS for the qualitative analysis of complex mixtures, as targets do not need modification and analysis requires only a few minutes. In addition, GC-MS is suitable for quantitative analysis.

Accelerating analysis for metabolomics, drugs and their metabolites in biological samples using multidimensional gas chromatography

Gas chromatography (GC) with mass spectrometry (MS) is one of the great enabling analytical tools available to the chemical and biochemical analyst for the measurement of volatile and semi-volatile compounds. From the analysis result, it is possible to assess progress in chemical reactions, to monitor environmental pollutants in a wide range of soil, water or air samples, to determine if an athlete or horse trainer has contravened doping laws, or if crude oil has migrated through subsurface rock to a reservoir. Each of these scenarios and samples has an associated implementation method for GC-MS. However, few samples and the associated interpretation of data is as complex or important as biochemical sample analysis for trace drugs or metabolites. Improving the analysis in both the GC and MS domains is a continual search for better separation, selectivity and sensitivity. Multidimensional methods are playing important roles in providing quality data to address the needs of analysts.

One-pot microwave derivatization of target compounds relevant to metabolomics with comprehensive two-dimensional gas chromatography

Metabolomics has been defined as the quantitative measurement of all low molecular weight metabolites (sugars, amino acids, organic acids, fatty acids and others) in an organism's cells at a specified time under specific environmental/biological conditions. Currently, there is considerable interest in developing a single method of derivatization and separation that satisfies the needs for metabolite analysis while recognizing the many chemical classes that constitute the metabolome. Chemical derivatization considerably increases the sensitivity and specificity of gas chromatography-mass spectrometry for compounds that are polar and have derivatizable groups. Microwave-assisted derivatization (MAD) of a set of standards spanning a wide range of metabolites of interest demonstrates the potential of MAD for metabolic profiling. A final protocol of 150 W power for 90 s was selected as the derivatization condition, based upon the study of each chemical class. A study of the generation of partially derivatized components established the conditions where this could potentially be a problem; the use of greater volumes of reagent ensured this would not arise. All compounds analyzed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry in a standard mixture showed good area ratio reproducibility against a naphthalene internal standard (RSD<10% in all but one case). Concentrations tested ranged from 1 microg/mL to 1000 microg/mL, and the calibration curves for the standard mixtures were satisfactory with regression coefficients generally better than 0.998. The application to gas chromatography-quadrupole mass spectrometry and comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry for a typical reference standard of relevance to metabolomics is demonstrated.

Simultaneous determination of blood glucose and isoleucine levels in rats after chronic alcohol exposure by microwave-assisted derivatization and isotope dilution gas chromatography/mass spectrometry

Blood glucose and isoleucine are two biomarkers of chronic alcohol exposure. Simultaneous determination of blood glucose and isoleucine levels helps to illuminate the influence of alcohol on the metabolism of glucose and amino acids. The most accurate method for the detection of serum glucose is isotope dilution gas chromatography/mass spectrometry (ID GC/MS). In this study, a rapid, simple and sensitive technique was developed for the quantitative analysis of glucose and isoleucine in rats after chronic alcohol exposure by microwave-assisted derivatization (MAD) and ID GC/MS. Serum glucose and isoleucine were rapidly derivatized by N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA) with microwave irradiation, and the trimethylsilyl derivatives were analyzed by GC/MS. This technique was used to demonstrate that pyrroloquinoline quinone (PQQ), a non-covalently bound prosthetic group in some quinoproteins involved in the metabolism of some sugar or alcohol, could reverse alcohol exposure induced glucose elevation. On the other hand, it did not affect the metabolism of isoleucine whose level was elevated along with serum glucose. The combination of MAD and ID GC/MS has been shown to be an accurate, rapid, simple and sensitive method for the quantification of glucose and isoleucine in serum samples.

Recent developments in sample preparation for chromatographic analysis of carbohydrates

Carbohydrates are a very important group of compounds due to their roles as structural materials, sources of energy, biological functions and environmental analytes; they are characterized by their structural diversity and the high number of isomers they present. While many advances have been made in carbohydrate analysis, the sample preparation remains difficult. This review aims to summarize the most important treatments which have been recently developed to be applied prior to the analysis of carbohydrates by chromatographic techniques. Due to the multiplicity of structures and matrices, many different techniques are required for clean-up, fractionation and derivatization. A number of new techniques which could be potentially adequate for carbohydrate characterization have also been revised.

Fluorescent sensing layer for the determination of L-malic acid in wine

An enzymatic method for determining L-malic acid in wine based on an L-malate sensing layer with nicotinamide adenine dinucleotide (NAD+), L-malate dehydrogenase (L-MDH) and diaphorase (DI), immobilized by sol-gel technology, was constructed and evaluated. The sol-gel glass was prepared with tetramethoxysilane (TMOS), water and HCl. L-MDH catalyzes the reaction between L-malate and NAD+, producing NADH, whose fluorescence (lambdaexc=340 nm, lambdaem=430 nm) could be directly related to the amount of L-malate. NADH is converted to NAD+ by applying hexacyanoferrate(III) as oxidant in the presence of DI. Some parameters affecting sol-gel encapsulation and the pH of the enzymatic reaction were studied. The sensing layer has a dynamic range of 0.1-1.0 g/L of L-malate and a long-term storage stability of 25 days. It exhibits acceptable reproducibility [sr(%) approximately 10] and allows six regenerations. The content of L-malic acid was determined for different types of wine, and polyvinylpolypyrrolidone (PVPP) was used as a bleaching agent with red wine. The results obtained for the wine samples using the sensing layer are comparable to those obtained from a reference method based on UV-vis molecular absorption spectrometry, if the matrix effect is corrected for.

Single-drop microextraction followed by in-syringe derivatization and gas chromatography-mass spectrometric detection for determination of organic acids in fruits and fruit juices

A simple analytical procedure based on single-drop microextraction combined with in-syringe derivatization and GC-MS was developed for determination of some phenolic acids in fruits and fruit juices. Cinnamic acid, o-coumaric acid, caffeic acid, and p-hydroxybenzoic acid were used as model compounds. The analytes were extracted from a 3-mL sample solution using 2.5 microL of hexyl acetate. The extracted phenolic acids were derivatized inside the syringe barrel using 0.7 microL of N,O-bis(trimethylsilyl)acetamide before injection into the GC-MS. The influence of derivatization conditions on the yield of in-syringe silylation was studied. Experimental SDME parameters such as selection of organic solvent, solvent volume, extraction time, extraction temperature, pH, and ionic strength of the solution on the extraction performance were studied. The method provided fairly good precision for all compounds (2.4-11.9%). Detection limits were found to be between 0.6 and 164 ng/mL within an extraction time of 20 min in the GC-MS full scan mode.