Ion chromatographic determination of organic acids in food samples using a permanent coating graphite carbon column

From the viewpoint of a graphite carbon column with excellent durability, it was applied to the ion chromatography (IC) of several organic acids. The carbon column was permanently coated with the cetyltrimethylammonium (CTMA) ion, and the elution behaviors of several organic acids (acetic acid, lactic acid, succinic acid, malic acid, tartaric acid, citric acid) and inorganic anions (Cl⁻, NO₂⁻, NO₃⁻, SO₄²⁻) were examined according to a non-suppressed IC coupled with conductivity detector, when an ion-exchange ability was given to the graphite carbon column. When salicylic acid and sodium salicylate were used as a mobile phase, each organic acid are analyzed approximately 10 min. But the separation of malic acid, chloride and nitrite was difficult. When benzoic acid and 2-amino-2-hydroxymethyl-1,3-puropanediol (tris aminomethane) were used as a mobile phase, tartaric acid and citric acid, etc. with large valency showed tendency to which the width of each peaks extended and retention time increased. However, it was possible to separate excellently for the analytes detected within 10 min. The developed method was then applied to the determination of organic acids in several food samples.     

The use of sulfamic acid as a primary standard in nonaqueous titrimetry

A method has been developed for the standardization of a typical nonaqueous base lithium methoxide, with an inorganic primary standard, sulfamic acid. 'T'his acid was found to dissolve readily in four independant basic solvents, dimethyl formamide, ethylenediamine, n-butylamine and dimethyl sulfoxide. Sulfamic acid could be titrated in each of these solvents, by both visual and potentiometric means with lithium methoxide dissolved in benzene-methanol. No gels nor precipitates resulted in the course of the titrations and the accuracy of the method was comparable to that obtained using benzoic acid as the primary standard. Conductometric titrations were also performed using sulfamic acid dissolved in two systems, dimethyl formamide and glacial acetic acid. In the latter solvent it was possible to titrate sulfamic acid with perchloric acid in glacial acetic acid.     

Synthesis of polyamides by the polyaddition of bisimidazoline with dicarboxylic acids

N,N′-Dipropionylethylenediamine was synthesized by the ring-opening addition reaction of 2-ethyl-2-imidazoline with propionic acid at 220°C. By applying this reaction to polymerization, polyamides were synthesized by the ring-opening polyaddition reaction at 220°C. of 1,4-bis(imidazoline-2-yl)butane with adipic acid, succinic acid, sebacic acid, and terephthalic acid. The reaction product of 1,4-bis(imidazoline-2-yl)butane with adipic acid, which was proposed to be nylon 26, was compared with an authentic sample of nylon 26 and shown to possess a very similar infrared spectrum and melting point.     

Optimization of the process of chemical hydrolysis of cellulose to glucose

We studied the acid hydrolysis of cellulose in an aqueous medium with the aim of maximizing glucose yield and minimizing the formation of by-products. The influence of reaction parameters such as temperature, acid concentration, acid strength and type of cellulose precursor on glucose yield was investigated. We observed that moderate reaction temperature and low acid concentration resulted in the highest glucose yield with little formation of levulinic acid. Strong acid (pKa < 0) is required to achieve high glucose yield. The crystallite size of the cellulose also affects its reactivity; cellulose with higher crystallite size is more resistant to hydrolysis catalyzed by acid. The highest selectivity for glucose over levulinic acid was recorded at a reaction temperature of 413 K and a sulfuric acid concentration in the range of 0.2–0.5 mol/L. Under these reaction conditions, no levulinic acid was detected, but the glucose yield reached 20 % in only 2 h.     

Synthesis and Hepatic Metabolism of Xanthobilirubinic Acid Regioisomers

Summary.  A set of four regioisomeric dipyrrinone propionic acids has been synthesized and their hepatic metabolism examined in rats: xanthobilirubinic acid and pseudo-xanthobilirubinic acid each with a propionic acid on a pyrrole ring; exo-ψ-xanthobilirubinic acid and endo-ψ-xanthobilirubinic acid, each with a propionic acid transposed to a lactam ring. After intravenous injection all four isomers were excreted to some degree in unchanged form in bile in normal rats. Xanthobilirubinic acid, the structurally closest dipyrrinone to bilirubin, and exo-ψ-xanthobilirubinic acid were excreted almost entirely in unchanged form. However, a small fraction of xanthobilirubinic acid acyl glucuronide was also detected. More extensive acyl glucuronidation was observed for pseudo-xanthobilirubinic acid, and endo-ψ-xanthobilirubinic acid underwent slow metabolism to unidentified more polar products that did not seem to be glucuronides.     

Furopyridines. I. Synthesis of furo[2,3-c]pyridine

The parent framework of furo[2,3-c]pyridine has been synthesized. 3-Furoic acid chloride ( 2 ) was reduced with bis(triphenylphosphine) copper(1) tetrahydroborate to afford 3-furaldehyde ( 3 ) which was condensed with malonic acid to give β-(3-furyl)acrylic acid ( 4 ). The acrylic acid 4 was converted to the acid azide ( 5 ), which in turn was cyclized to give furo[2,3-c]pyridin-7(6H)-one ( 6 ) by heating at 180° in diphenylmethane. The pyridone 6 was chlorinated with phosphorus oxychloride, followed by reduction with zinc and acetic acid to give furo[2,3-c]pyridine ( 8 ).     

Degradation of benzoic acid and its derivatives in subcritical water

In this research, the stability of benzoic acid and three of its derivatives (anthranilic acid, salicylic acid, and syringic acid) under subcritical water conditions was investigated. The stability studies were carried out at temperatures ranging from 50 to 350 °C with heating times of 10–630 min. The degradation of the benzoic acid derivatives increased with rising temperature and the acids became less stable with longer heating time. The three benzoic acid derivatives showed very mild degradation at 150 °C. Severe degradation of benzoic acid derivatives was observed at 200 °C while their complete degradation occurred at 250 °C. However, benzoic acid remained stable at temperatures up to 300 °C. The degradation products of benzoic acid and the three derivatives were identified and quantified by HPLC and confirmed by GC/MS. Anthranilic acid, salicylic acid, syringic acid, and benzoic acid in high-temperature water underwent decarboxylation to form aniline, phenol, syringol, and benzene, respectively.     

Sequential injection redox or acid-base titration for determination of ascorbic acid or acetic acid

Two sequential injection titration systems with spectrophotometric detection have been developed. The first system for determination of ascorbic acid was based on redox reaction between ascorbic acid and permanganate in an acidic medium and lead to a decrease in color intensity of permanganate, monitored at 525 nm. A linear dependence of peak area obtained with ascorbic acid concentration up to 1200 mg l⁻¹ was achieved. The relative standard deviation for 11 replicate determinations of 400 mg l⁻¹ ascorbic acid was 2.9%. The second system, for acetic acid determination, was based on acid–base titration of acetic acid with sodium hydroxide using phenolphthalein as an indicator. The decrease in color intensity of the indicator was proportional to the acid content. A linear calibration graph in the range of 2–8% w v⁻¹ of acetic acid with a relative standard deviation of 4.8% (5.0% w v⁻¹ acetic acid, n=11) was obtained. Sample throughputs of 60 h⁻¹ were achieved for both systems. The systems were successfully applied for the assays of ascorbic acid in vitamin C tablets and acetic acid content in vinegars, respectively.     

Microsphere resin chromatography combined with microbial biotransformation for the separation and purification of salvianolic acid B in aqueous extract of roots of Salvia multiorrihza Bunge

Salvianolic acid B was separated and purified from Salvia miltiorrhiza Bunge (danshen) by microbial transformation together with chromatography of microsphere resin. The aqueous extract of danshen was transformed by Fusarium graminearum in a bioreactor containing phosphate buffer (PBS), in which rosmarinic acid was transformed into danshensu and caffeic acid and the yield of salvianolic acid B was higher than 85%. After biotransformation, salvianolic acid B was purified by microsphere resin. A parallel test for making a comparison of microsphere resin chromatography between elution by methanol water solution and water was done. The purity of salvianolic acid B was up to 95% at the yield of 62% when impurities and salvianolic acid B were eluted by 45% and 55% methanol solution respectively. The purity of salvianolic acid B was up to 99% at the yield of 90% when distilled water was used to elute the impurities and salvianolic acid B. The total yield of salvianolic acid B was up to 75% at the purity over 99% while biotransformation combined with microsphere resin chromatography by water elution. Microbial biotransformation together with water elution of microsphere resin supplied an efficient method to eliminate the micromolecular impurities and a possible method to purify water-soluble compounds in traditional Chinese medicine.     

Isolierung,Konstitution und Synthese der (R)-(−)-Eucominsäure

From the bulbs of Eucomis punctata L'Hérit. (Liliaceae) and of a hitherto undefined species of Eucomis a new optically active phenolic carboxylic acid, eucomic acid, was isolated. Structure 1 was assigned on the basis of chemical and spectral evidence. The absolute configuration of eucomic acid was determined by its correlation with piscidic acid ((2 R, 3 S)-2-(4′-hydroxybenzyl)-tartaric acid) ( 8 ). Consequently, eucomic acid is (R)-(?)-2-(4′-hydroxybenzyl)-malic acid ( 1 ). For the stereospecific synthesis, methyl cis-p-methoxybenzylidene-succinic acid ( 22 ) was transformed into the γ-lactone 24 which, by catalytic hydrogenolysis, yielded (±)-2-(4′-hydroxybenzyl)-malic acid 1-methyl ester ( 27 ). Resolution with (?)-quinine led to the enantiomeric acids 29 and 30 . The methyl ester of the levorotatory enantiomer 30 was identical with the dimethyl ester 3 of 4′-O-methyl-eucomic acid.     

The mechamism of action of vitamin B12

A novel rearrangement reaction is introduced as a model for the rearrangement of methylitaconic acid (III) to α-methyleneglutaric acid (IV), one of three enzyme catalyzed, coenzyme B₁₂-dependent, carbonskeleton rearrangements whose mechanism has been a source of puzzlement for many years. The key feature of the new model is the direct attachment of the substrate, methylitaconic acid, to the cobalt atom of vitamin B₁₂ This was accomplished by reacting butadiene-2,3-decarboxylic acid with hydrobromic acid generating bromomethylitaconic acid (VIII). Use of two moles of hydrobromic acid yielded bis-2,3-(bromomethyl)succinic acid (IX). Reaction of the monobromide VIII with vitamin B_12s did not yield the desired carbon-cobalt bonded adduct. Instead, the lactone ηa- methylene-γbutyrolactone-β-carboxylic acid (X) was formed. Accordingly, the ester, dimethyl bromomethylitaconate (XIa), was reacted with vitamin B_12s and yielded the carbon-cobalt bonded adduct XIIa. Bis-trimethylsilyl bromomethylitaconate did not yield an adduct when reacted with vitamin B_12s, but bis-tetrahydropyranyl bromomethylitaconate (XIb) did yield the adduct XIIb. The ester cobalamin XIIb undergoes spontaneous decomposition at room temperature, in aqueous solution, at pH 8 and in the dark - biochemically ideal circumstances - yielding a mixture of butadiene-2,3-decarboxylic acid (VII), methylitaconic acid (III) and α- methyleneglutaric acid (IV). The presence of the latter indicates that a skeletal change has taken place in a way which mimics the enzymatic reaction. This is the first non-enzymic model in this carbon-skeleton rearrangement series. The methyl ester cobalamin XIIa was stable in the dark but did decompose on irradiation with a sunlamp to butadiene-2,3decarboxylic acid (VII) and methylitaconic acid (III). No α-methyleneglutaric acid IV was observed in the latter reaction.Authentic methylitaconic acid (III) was prepared by alkylation of triethyl prop-2-ene-l,l,2-tricarboxylate (XIII) with methyl iodide followed by hydrolysis and decarboxylation. The lactone X and lactone α-methyl-γ-butyrolactone-β-carboxylic acid (XVI) were prepared by condensing the triester XIII with formaldehyde, hydrolyzing the lactone diester XV to the lactone X and hydrogenating to the saturated lactone XVI.     

Antianexiety activity of pyridine derivatives synthesized from 2-chloro-6-hydrazino-isonicotinic acid hydrazide

A series of oxadiazole pyridine derivatives were synthesized by using 2-chloro-6-hydrazinoisonicotinic acid hydrazide as starting material. Treatment of the hydrazide with carbon disulfide to afford the oxadiazole derivative, which was treated with 5-methyl-2-furancarbaldehyde, formic acid, acetic acid/acetic anhydride, or phthalic anhydride to yield the corresponding pyridinodiazoles and on imide. Condensation of the hydrazide with p-fluorobenzaldehyde in ethanol or acetic acid in the presence of sodium acetate afforded hydrazone and oxadiazole derivatives, which were acetylated and cyclized with acetic anhydride to N-acetyloxadiazole derivatives. The hydrazone was treated with acetic acid in the presence of sodium acetate, or bromine water/sodium acetate to give on oxadiazole, while it was cyclized with chloroacetyl chloride in the presence of TEA to oxoazetidinaminoisonicotinamide. Finally, condensation of the hydrazide with acid anhydrides in refluxing glacial acetic acid afforded the corresponding bisimide derivatives. The pharmacological screening showed that many of these obtained compounds have good antianexiety activity comparable to diazepam^® as positive control.     

Degradation of uric acid and 3-ribosyluric acid during treatment with charcoal

Uric acid and 3-ribosyluric acid at a concentration of 1.5 × 10^?4M were quantitatively adsorbed to charcoal, but were not recovered when the charcoal was washed with ethanol:water:NH₄OH (60:36:4), a solvent which readily eluted a number of other bases and nucleosides. With [2-¹⁴C]uric acid it was shown that the radioactivity was adsorbed to the charcoal and that [¹⁴C]allantoin was the primary product recovered after elution. Incubation of uric acid or 3-ribosyluric acid in the ethanol:water:NH₄OH did not result in any degradation. The elution of uric acid from charcoal with other eluents such as 7% phenol, 0.1 M NaOH, or ethanol:water:pyridine (50:40:10) also resulted in the conversion of uric acid to allantoin. It was concluded that when uric acid and 3-ribosyluric acid are adsorbed to charcoal and then eluted, there is a substantial conversion of these compounds to the corresponding allantoin.     

Determination of Indole-3-acetic Acid and Abscisic Acid by Double-Direction Dispersive Liquid–Liquid Microextraction Coupled with High-Performance Liquid Chromatography

A method for the separation and purification of indole-3-acetic acid and abscisic acid based on double-direction dispersive liquid–liquid microextraction coupled with high-performance liquid chromatography was developed. The reverse-direction dispersive liquid–liquid microextraction procedure was very efficient in the purification of the hormones. The forward-direction dispersive liquid–liquid microextraction procedure was very efficient in the enrichment of the analytes. Under optimum conditions, a linear response was observed over the ranges of 0.2 µg/g to 200.0 µg/g for indole-3-acetic acid and 0.1 µg/g to 200.0 µg/g for abscisic acid, with correlation coefficients of 0.9967 and 0.9983. The limits of detection for indole-3-acetic acid and abscisic acid were 0.02 µg/g and 0.01 µg/g. The recoveries by standard addition were 91.4% and 88.6% for indole-3-acetic acid and abscisic acid with corresponding relative standard deviations of 4.5% and 6.1% (n = 5). The developed method was used for the preconcentration and determination of indole-3-acetic acid and abscisic acid in Arabidopsis thaliana, and satisfactory results were obtained.     

Monitoring of vitamin C species in aqueous solution by flow injection analysis coupled with an on-line separation with reversed-phase column

Two vitamin C species of ascorbic acid and dehydroascorbic acid in aqueous solution were monitored by flow injection analysis. Ascorbic acid and dehydroascorbic acid were resolved by a reversed-phase column, and dehydroascorbic acid was reduced to ascorbic acid by an on-line post-column reaction with dithiothreitol. Both natural and reduced ascorbic acids were photometrically detected at 260 nm, and the two vitamin C species were simultaneously determined. The determination range was from 0 to 8 × 10⁻⁵ M with a limit of detection of 1.7 × 10⁻⁶ M. The proposed method was applied to the conversion monitoring of ascorbic acid and dehydroascorbic acid in weakly acidic to weakly alkaline aqueous solutions, as well as to the determination of the vitamin C in some beverage samples.     

Determination of the enantiomers of α‐hydroxy‐ and α‐amino acids in capillary electrophoresis with contactless conductivity detection

The enantiomers of the anions of five α‐hydroxy acids, namely lactic acid, α‐hydroxybutyric acid, 2‐hydroxycaproic acid, 2‐hydroxyoctanoic acid and 2‐hydroxydecanoic acid, as well as the two α‐amino acids aspartic acid and glutamic acid, were baseline separated and detected by CE with contactless conductivity detection. Vancomycin was employed as chiral selector and could be used with conductivity detection without having to resort to a partial filling protocol as needed when this reagent is used with UV absorbance measurements. The procedure was successfully applied to the determination of the lactic acid enantiomers in samples of milk and yogurt. Linearity was achieved in the concentration range of 10–500 μmol/L with good correlation coefficients (0.9993 and 0.9990 for L ‐ and D ‐lactic acid, respectively). The LODs (3 S/N) for L ‐ and D ‐lactic acid were determined as 2.8 and 2.4 μmol/L, respectively.     

Liquid-liquid extraction separation of uranium(VI) from associated elements using dibenzo-24-crown-8 from hydrobromic acid medium

Liquid-liquid extraction of uranium (VI) from hydrobromic acid solutions with dibenzo-24-crown-8 in nitrobenzene have been investigated. Uranium(VI) was quantitatively extracted from 6.0–8.0M hydrobromic acid with 0.001–0.01M dibenzo-24-crown-8 and was quantitatively stripped from the organic phase with 0.1–1.0M hydrochloric acid, 0.5–10M nitric acid, 2–10M perchloric acid, 3.0–10M sulfuric acid or 3.0–10M acetic acid. It was possible to separate uranium(VI) from a number of elements in binary mixtures. Most of the elements showed very high tolerance limit Uranium(VI) was also separated from a number of associated elements in multicomponent mixtures. The method is very simple, selective, rapid and highly reproducible (approximately±2%) and was applied to the analysis of uranium in geological samples.     

Sulfur-containing carboxylic acids. 6. The syntheses of 3,3"-sulfinyldipropionic and 2,2"-sulfinyldiacetic acids

Pure sulfoxides of thiodialiphatic acids were obtained in high yields by oxidation of the corresponding sulfides in organic solvents. 3,3"-Sulfinyldipropionic acid was obtained by the reaction of hydrogen peroxide with thiodipropionic acid in acetone. 2,2"-Sulfinyldiacetic acid was synthesized by the reaction of thiodiglycolic acid with H₂O₂ in acetone containing acetic acid (26 mol. %). Pure 2,2"-sulfinyldiacetic acid was found to be stable in storage rather than labile as reported previously.     

Treatment of phosphate rocks with hydrochloric acid

Phosphate rocks were leached with hydrochloric acid; and radium was removed by co-precipitation with BaSO₄. Uranium and lanthanides were extracted by di(2-ethyl hexyl) phosphoric acid and tributyl phosphate. Phosphoric acid was then separated from calcium chloride solution and other impurities by extraction using undiluted iso-amyl alcohol. Gypsum was precipitated by sulfuric acid to regenerate hydrochloric acid for recycling. Fluorine was precipitated from the initial leach solution as Na₂SiF₆.