A review of the determination of organic compounds in Bayer process liquors

Bayer process liquors present a difficult and complex matrix to the analytical chemist, and the history of the application of modern analytical techniques to this problem is a case study in innovation. All Bayer process liquors contain organic compounds, in amounts varying from traces to several grams per litre. The total organic carbon content of Bayer liquors may be less than 5 g/L up to as much as 40 g/L. The presence of these organic impurities is of concern to Bayer technologists because they can have significant impacts on the economics of the process and the quality of the product. This review examines the history and current state-of-the-art of the analysis of organics in Bayer process liquors, and provides guidance on the applicable techniques matched to a comprehensive list of the compounds most likely to be present.     

Determination of low molecular weight organic acids in soil solution by HPLC

An HPLC method employing an ion exclusion column was developed for the determination of low molecular weight organic acids in soil solution. The method includes extensive sample pretreatment using ultrafiltration and cation exchange. The method showed linear calibration graphs (r>0.99) and the limits of detection in the range 0.1-26 muM. The recovery of eleven added acids ranged from 89 to 102%. Soil solutions of five horizons of a podzolised soil were analysed. The results showed that these compounds made up 1-3% of the dissolved organic carbon and 0-14% of the acidity. Identification of the major acids was also carried out by capillary zone electrophoresis.     

Characterization of low molecular weight organic acids from beech wood treated in supercritical water

Japanese beech (Fagus crenata Blume), its cell wall components, and model compounds were treated by supercritical water (380°C, 100 MPa) for 5 s using a batch-type reactor to investigate the production behavior of low molecular weight organic acids. It was found that cellulose and hemicellulose were decomposed to formic acid, pyruvic acid, glycolic acid, acetic acid, and lactic acid, whereas lignin was barely decomposed to such organic acids under the given conditions. However, after prolonged treatment (380°C, 100 MPa, 4 min) of lignin, some organic acids were recovered owing perhaps to the decomposition of the propyl side chain of lignin. It was additionally revealed that the predominant organic acid recovered was acetic acid, which might be derived from the acetyl group of hemicellulose in Japanese beech.     

Determination of organic acids of low molecular weight and phosphate in soil by capillary electrophoresis

Capillary zone electrophoresis with indirect UV detection at 254 nm was found to be suitable for the determination of organic acids and phosphate in aqueous extracts of soil. The best support electrolyte solution was found to be 10 mM p-hydroxybenzoic acid with 0.5 mM tetradecyltrimethylammonium bromide to reverse electroosmotic flow. This methodology was tested with 9 analytes found in soils: acetate, citrate, formate, phosphate, lactate, oxalate, pyruvate, succinate, and tartrate. The results obtained show that the methodology is adequate for most of the analytes. The sensitivity to oxalate and citrate was low, and the high concentrations of major inorganic anions interfered with the detection of the former. The methodology was applied to the analysis of aqueous extracts of soil samples. Formate, phosphate, lactate, and acetate anions were detected in most of the samples.     

Interaction between low molecular weight organic acids and hydroxyapatite with different degrees of crystallinity

In this study, two types of hydroxyapatite (HAP) with different degrees of crystallinity were prepared by a sol-gel method and a chemical precipitation method. Influences of crystallinity on the adsorption and dissolution properties of HAP, and the release of phosphorus (total phosphorus) during the adsorption of organic acid were investigated. Results showed that crystallinity had a great effect on the adsorption capacity and dissolution properties of HAP, as well as the adsorption mechanisms of organic acids on HAP surfaces. The poorly crystallized (the degree of crystallinity X_c = 0.23) HAP adsorbed greater amounts of oxalic, citric, or malic acid than the well crystallized (X_c = 0.86) HAP, and the former could release more phosphorus in the presence of organic acids. The adsorption capacity of oxalic acid was much higher than citric and malic acids on both the well and the poorly crystallized HAP, which was due to the strong coordination of oxalic acid with calcium on HAP surface, and that physical adsorption was more inclined to dominate the adsorption of malic or citric acid on the well crystallized HAP. These findings might be of importance in understanding the effects of crystallinity and organic acid binding on the dissolution of calcium phosphates and the adsorption characteristics of HAP.     

A novel method for determination of low molecular weight dicarboxylic acids in background atmospheric aerosol using ion chromatography

This paper describes a novel gradient elution ion chromatographic method using a Dionex AS11 system for the determination of low molecular weight dicarboxylic acids (low-M_w DCAs) in background atmospheric aerosol. Interference with the oxalic acid peak from sulfate in background PM_2.5 aerosol, 15.8 times the oxalic acid concentration, was remedied by removing sulfate using a barium cartridge, whilst interference with the malonic acid peak from carbonate was reduced by using a carbonate removal device. An alternative remedy to sulfate interference was use of an AS14 system using isocratic eluent, and this produced good resolution of oxalic acid from a high sulfate peak. In both the AS11 and the AS14 system, linear correlation coefficients were at all times >0.9990 with excellent linear range, the recoveries ranged from 92.8 to 106%, with relative standard deviation of 3.67-6.30%, whilst method detection limits (MDLs) ranged from 0.36 μg L⁻¹ for malic acid to 3.87 μg L⁻¹ for maleic acid. These data indicate that the analytical methods developed herein produce excellent separation efficiency and good determination of low-M_w DCAs with satisfactory accuracy, recoveries, and MDLs. Samples left at room temperature (20 °C) for 300 min in a simulation of the ‘waiting time’ involved in the proposed IC analysis decayed to between 86% (oxalic acid) and 39% (succinic and malonic acids) of their original concentration, whilst at 4 °C concentrations remained at 96-101% of original, indicating that maintaining samples at a low temperature prior to injection into the IC analyzer is vital for obtaining accurate results when analyzing low-M_w DCAs. Oxalic acid was found to be the most prevalent low-M_w DCA in background aerosol, comprising 57% of the total low-M_w DCAs and 0.959% of the PM_2.5 aerosol mass, followed by succinic acid and malonic acid.     

Analysis of low molecular weight organic acids in water with capillary zone electrophoresis employing indirect photometric detection

A capillary zone electrophoretic method for the analysis of low molecular weight carboxylic acids in water was developed. The application uses the chromophore trimellitic acid that allows for indirect photometric detection at 254 nm. Selectivity control by the addition of Ca2+ to the carrier electrolyte made possible a baseline resolved separation of 14 carboxylic acids. Good linearity and repeatability were obtained for both electrokinetic and hydrostatic injection modes. The usefulness of the method is demonstrated by the analysis of a snow sample.     

An improved method for the extraction of low molecular weight organic acids in variable charge soils.

Due to specific adsorption to variable charge soils, low molecular weight organic acids (LMWOAs) have not been sufficiently extracted, even if common extractants, such as water and 0.1 M sodium hydroxide (NaOH), were employed. In this work, the method for extracting LMWOAs in soils with 0.1 M NaOH was improved for variable charge soils; e.g. 1.0 M potassium fluoride (KF) with pH 4.0 was applied as an extractant jointed with 0.1 M NaOH based on its stronger ability to change the electrochemical properties of variable charge soils by specific adsorption. With the proposed method, the recoveries of oxalic, tartaric, malic, citric and fumaric acids were increased from 83 +/- 4, 93 +/- 1, 22 +/- 2, 63 +/- 5 and 84 +/- 3% to 98 +/- 2, 100 +/- 2, 85 +/- 2, 90 +/- 2 and 89 +/- 2%, respectively, compared with NaOH alone. Simultaneously, the LMWOAs in Agri-Udic Ferrosol with field moisture were measured with a satisfactory result.     

Analysis of low molecular weight organic acids in water with capillary zone electrophoresis employing indirect photometric detection

A capillary zone electrophoretic method for the analysis of low molecular weight carboxylic acids in water was developed. The application uses the chromophore trimellitic acid that allows for indirect photometric detection at 254 nm. Selectivity control by the addition of Ca²⁺ to the carrier electrolyte made possible a baseline resolved separation of 14 carboxylic acids. Good linearity and repeatability were obtained for both electrokinetic and hydrostatic injection modes. The usefulness of the method is demonstrated by the analysis of a snow sample.     

Capillary electrophoresis with capacitively coupled contactless conductivity detection for low molecular weight organic acids in different samples

CE with capacitively coupled contactless conductivity detection (CE-C(4)D) was explored and validated for the identification and quantification of organic acids in various types of samples. The analyses were performed under optimized conditions, using a buffer system composed of 20 mM MES-histidine (His), pH 6.0, 0.1 mM CTAB, 0.025% HP-beta-CD, and 10% methanol. The investigation included a study of the effects of buffer pH, concentration of CTAB, type and concentration of organic additives, on the migration behavior, resolution and selectivity of the organic acids. The intra- and interday RSDs (n = 6) obtained for migration time and peak area were typically in the range of 0.12-2% and 0.5-4%, respectively. Linearity, detection limits, and repeatability were evaluated. In order to evaluate the application potential of the developed method, real samples from different sources were analyzed. The results demonstrate that CE-C(4)D is a versatile tool for analyzing organic acids in beverages, Chinese herbal medicines (CHM) and plants as it allows for their detection, identification, and quantification.     

Stigmasterol-based novel low molecular weight/mass organic gelators

Conjugates consisting of stigmasterol and L-phenylalanine, interconnected through short-chained dicarboxylic acyls by ester and amide bonds, respectively, were synthesized as potential low molecular weight/mass organic gelators (LMWGs/LMMGs). Their physico-chemical properties were subjected to investigation, especially their ability to form gels reversibly based on changes of the environmental conditions. Other self-assembly properties detectable by UV-VIS traces were measured in systems consisting of two miscible solvents (water/acetonitrile) with varying solvent ratios and using constant concentrations of the studied compounds. Partition and diffusion coefficients and solubility in water were calculated for the target conjugates. The conjugate 3a was the only compound from this series capable of forming a gel in 1-octanol. All three conjugates 3a-3c displayed supramolecular characteristics in the UV-VIS spectra.     

Determination of low molecular weight organic acids in soil,plants, and water by capillary zone electrophoresis

Determination of low molecular weight organic acids in soils and plants by capillary zone electrophoresis was accomplished using a phthalate buffer and indirect UV detection mode. The influence of some crucial parameters, such as pH, buffer concentration and surfactant were investigated. A good separation of seven organic acids was achieved within 5 min using an electrolyte containing 15 mmol L(-1) potassium hydrogen phthalate, 0.5 mmol L(-1) myristyltrimethylammonium bromide (MTAB), and 5% methanol (MeOH) (v/v) at pH 5.60, separation voltage -20 kV, and temperature 25 degrees C. The relative standard deviation (n=5) of the method was found to be in range 0.18-0.56% for migration time and 3.2-4.8% for peak area. The limit of detection ranged between 0.5 micro mol L(-1) to 6 micro mol L(-1) at a signal-to-noise ratio of 3. The recovery of standard organic acids added to real samples ranged from 87 to 119%. This method was simple, rapid and reproducible, and could be applied to the simultaneous determination of organic acids in environmental samples.     

A convenient parallel synthesis of low molecular weight hydroxamic acids using polymer-supported 1-hydroxybenzotriazole

A convenient two-step procedure for the parallel synthesis of hydroxamic acids from carboxylic acids and hydroxylamine in good to high yields is reported. It involves the formation of a polymer-bound HOBt active ester and subsequent reaction with O-protected or free hydroxylamine. The hydroxamates are isolated with high purities by simple evaporation of volatile solvents. The use of free hydroxylamine leads to increased yields while maintaining high purities. Recycling of the spent resin to produce the same or a different hydroxamic acid has been achieved by a three-step protocol which is easily amenable to automation and cost-economical. The method presented here is well suited to the preparation of the title compounds and can be used effectively to synthesise large molecules containing a hydroxamic acid group.     

毛细管离子色谱-串联质谱法测定热纤梭杆菌发酵液中的低相对分子质量有机酸

建立了一种测定热纤梭杆菌发酵液中的低相对分子质量有机酸的毛细管离子色谱-串联质谱方法。探索优化了色谱和质谱的检测条件,在最佳分析条件下同时检测8种有机酸。离子色谱以KOH水溶液作为流动相进行梯度洗脱;用IonSwift MAX-100毛细管柱进行分离;在喷雾电压为3.0 kV、喷雾气压强为2 000 kPa、成源温度为275℃的条件下,选择离子监测(SIM)模式下运行质谱。结果表明,柠檬酸和异柠檬酸两种同分异构体能够得到很好的分离,8种有机酸在一定浓度范围内具有良好的线性关系,相对标准偏差为1.45%~5.99%,相关系数为0.9696~0.9986,平均加标回收率为89.0%~110.0%,8种有机酸的检出限为0.01~0.50 mg/L。该方法进样量少,灵敏度高,重现性好,能够满足实际样品的检测要求,可用于嗜热厌氧菌发酵液中低分子量有机酸的测定。     

Separation and determination of organic acids and inorganic anions in Bayer liquors by ion chromatography after solid-phase extraction

An ion chromatographic (IC) method for the determination of six organic acids and three inorganic anions in Bayer liquors was proposed. Formic, acetic, propionic, oxalic, succinic, glutaric acid, F⁻, Cl⁻, and SO ₄ ²⁻ were separated and determined within 33 min. For the first time, repeatability, reproducibility, and recoveries for the determination of these acids in Bayer liquors were estimated. The analytes were removed from a Bayer liquor by using an ion-exchange resin column. The chromatographic separation was achieved with only one IonPac AS11-HC column thermostated at 30°C. Organic acids and inorganic anions were detected with a suppressed conductance detector. The precision results showed that the relative standard deviations of the repeatability and reproducibility were <2.94 and <1.37%, respectively. The accuracy of the method was confirmed with an average recovery ranging between 86.3 and 105.6%. Under optimum conditions the detection limits ranged from 0.008 to 0.053 mg/L. The text was submitted by the authors in English.     

HPLC-method for the determination of a low molecular weight trypsin inhibitor in urine

Summary A method to analyse a low molecular weight trypsin inhibitor (UTI-L, apparent molecular weight: 6200) in human urine is described. The procedure consists of an enrichment step and a separation by RP-HPLC. The urine sample with aprotinin as internal standard is adjusted to pH 8.3 and percolated through a trypsin-Sepharose 4B column; the inhibitors are eluted with acid solution. This eluate is analysed by RP-HPLC with ultraviolet detector (200 nm). Starting with a known sample volume (ca. 200 ml) the detection limit of the whole analytical procedure is 0.02 IU _bapna 1^–1 of urine.

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HPLC-Methode zur Bestimmung eines niedermolekularen Trypsin-Inhibitors in Harn

     

Single-component,low molecular weight organic supergelators based on chiral barbiturate scaffolds

ABSTRACT

We report here the first chiral barbiturate to act as a single-component LMOG capable of gelating a variety of chlorinated and aromatic solvents. Solution-based DOSY NMR experiments, solid-state VP-SEM, and X-ray crystallography techniques were used to characterize chloroform-based gels at a variety of size domains. This scaffold provides a simple system to study the dynamics of gelation and self-assembly.     

Vacancies in the solids of low molecular weight organic compounds observed by positron annihilation

PAL were measured for several low molecular organic compounds, normal and cyclic-hydrocarbons and their perfluorinated ones, from room temperature down to about 40 K, and information about the vacancies in them has been extracted from ₃ andI ₃. Normally the size of vacancies were larger in the solids comprising larger molecules, showing thato-Ps can represent the vacancy size. In a special case of perfluorocyclohexane whose solid had to be prepared by sublimation the vacancy size was larger than expected. In all the solid molecules studied twoo-Ps states could be observed and their relative importance could easily change showing a hysteresis-like behavior. At further lower temperatures of around 40 K theo-Ps state with longer lifetime and larger intensity became overwhelming for all molecules. Also ₃ andI ₃ were not very sensitive to most of the phase transitions, including the melting points.