Comparison of Different Sorbents for Solid-Phase Extraction of Phenoxyalkanoic Acid Herbicides

An HPLC procedure for determination of phenoxyalkanoic acid herbicides in water samples is proposed. The analytical column Phenomenex C18(2) Luna 5 µm and UV detection at 225 nm were applied. Baseline resolution was achieved in isocratic mode with a mobile phase consisting of acetonitrile/acetic acid (40/60, v/v), adjusted to pH 2.5. SPE sorbents – C₁₈ BondElut, phenyl-silica, LiChrolut SAX and polymeric sorbents – were compared for isolation and preconcentration of 6 phenoxyalkanoic acid herbicides. Higher (above 95%) and more reproducible recoveries were obtained with polymeric and phenyl-silica sorbents using pure methanol for elution. The method was tested for river water samples with the limit of detection in the range of 2–3 µg L⁻¹ (for 50 mL sample) and a reproducibility of 5% RSD.     

Complexation in Benzo-15-Crown-5–Chloroform–Substituted Acetic Acid Extraction Systems

To study the complexing processes occurring in the extraction systems, the extraction of acetic, propionic (methylacetic), monochloroacetic, dichloroacetic and trichloroacetic acids using benzo-15- crown-5 as an extractant is considered. The extraction isotherms of acids with the pure solvent and 1 M benzo-15-crown-5 in chloroform are determined. The dependences of the distribution ratios of the considered acids on the extractant concentration in the organic phase are presented. Based on the experimental data and the “blank” extraction isotherm equations, the acid: benzo-15-crown-5 ratio in the complexes formed in the extract have been calculated (minus the contribution of extraction with the pure solvent). No complexation of methylacetic acid with benzo-15-crown-5 occurs, and the stability of the complexes of chloro-substituted acetic acids rises in the order acetic acid < monochloroacetic acid < dichloroacetic acid < trichloroacetic acid.     

FTIR Studies of the Adsorption of Acetic Acid on Silicas

A range of cesium doped silica samples (0.15 – 0.90 mmol g^–1) have been characterized using a combination of deuterium exchange and adsorption of acetic acid. FTIR results show a strong correlation between the carboxylate formation on acetic acid adsorption and catalyst activity. Cesium loadings of > 0.3 mmol g^–1 do not give any increased acetic acid adsorption, suggesting a saturation of the silica exchange capacity. Deuterium exchange studies demonstrate that 35% of the surface silanol groups on the fresh silica are rapidly exchanged with deuterated water at room temperature.     

Cathodic Hydrogen Evolution from Aqueous Solutions of Acetic Acid

In continuation of the work on establishing hydrogen donors in the hydrogen evolution reaction from different acid molecules, cathodic evolution of hydrogen on silver is investigated from solutions of monobasic acetic acid with the aim to establish the origin of reduced hydrogen. Solutions of 0.2 M acetic acid with 0.2 M perchloric acid, neutralized to different pH values by NaOH, are used. The earlier established criterion is used for discerning between two possible hydrogen evolution mechanisms: (1) from dissociated hydrogen ions and (2) from undissociated hydrogen atoms in the molecule. At medium pH values, the undissociated acid molecules participate as hydrogen donors. Rate constants for reactions 1 and 2, evaluated at a potential of –800 mV (SCE), at which the entire pH range can be scanned, are 2.9 × 10^–6 and 1.9 × 10^–8.     

The spectrophotometric determination of anions by solvent extraction with metal chelate cations. part XX : Trichloroacetic acid with tris(1,10-phenanthroline)iron(ii) chelate

Trichloroacetic acid can be extracted from an aqueous solution by nitrobenzene with tris(1,10-phenanthroline)iron(II) chelate, and can be determined spectrophotometrically by measuring the extract at 516 nm. The extracted species is probably [Fe(phen)₃].(CCl₃COO)₂. Beer's law is obeyed over the concentration range 1.0·10^-5–1.0·10^-4M trichloroacetic acid in aqueous solution. Large amounts of phosphate and sulfate and moderate amounts of chloride, acetic acid, and monochloroacetic acid do not interfere, equal amounts of dichloroacetic acid give a slight positive error     

Conductance of Dilute Sodium Acetate Solutions to 469 K and of Acetic Acid and Sodium Acetate/Acetic Acid Mixtures to 548 K and 20 MPa

In order to obtain accurate association constants for sodium acetate, a very precise flow method was used to measure the electrical conductivity of dilute aqueous solutions of sodium acetate at ambient conditions and 469 K and 20 MPa. Measurements at ambient conditions, 469 and 548 K and 20 MPa, were also made on sodium acetate/acetic acid mixtures and acetic acid. In order to determine the limiting the equivalent conductances and the association constant for sodium acetate, and dissociation constant for acetic acid, the results were fitted to two modern conductance equations (Fuoss–Hsia–Fernandez–Prini and Turq–Blum–Bernard–Kunz) with accompanying activity coefficient models (mean spherical approximation and the Debye–Hückel with the Bjerrum distance). The choice of conductance equation, activity coefficient model, assumed values for the limiting equivalent conductance for minor species, and assumed equilibrium constants for minor reactions, did not significantly change the resulting equilibrium constants. The insensitivity of the calculated equilibrium constants to these choices in conjunction with the inherent precision of the flow conductance technique leads us to believe that the present results are the most accurate sodium acetate ion-pairing constants published to date. Our results for acetic acid are in good agreement with previously published results from other laboratories.     

Acid–Base Interactions in the Dichloroacetic Acid–Ethyl Acetate System according to IR Spectroscopic Data

The method of multiple total internal reflection infrared spectroscopy (MTIRIRS) is used to study ion–molecular interactions in the system dichloroacetic acid–ethyl acetate in the range of concentrations from pure acid to pure base at 30°C. Depending on the ratio of components in the solution, molecular complexes with acid : base ratios of 1 : 1 or 2 : 1 are formed in the solutions. In the case of excess acid, base is not protonated and species with a strong symmetric hydrogen bond are not formed. It is shown that the absorption coefficient near 2000 cm^–1 can be used to judge the type of the complex formed and the strength of a hydrogen bond in molecular complexes.     

Determination of Glycolate Acid,Mono‐ and Dichloroacetic Acids in Synthetical Betaine by Anion‐exchange Chromatography

An anion‐exchange chromatography method combined solid phase extraction (SPE) was developed for the simultaneous analysis of glycolate acid (GL), monochloroacetic acid (MCA) and dichloroacetic acid (DCA) in synthetical betaine products. The analytes and unknown anionic impurities were well separated on a Metrosep A supp5 anion‐exchange column (150 mm×4 mm) with 2.0 mmol/L Na₂CO₃+2.0 mmol/L NaHCO₃ solution as eluent. Suppressed conductivity detection was used. A strong cation exchange (SCX) solid phase extraction (SPE) cartridge was used to reduce the concentration of matrix betaine and a Cleanert IC‐Ag pretreatment cartridge was used to remove high Cl^? concentration. The detection limits of GL, MCA and DCA were 0.09, 0.017 and 0.05 µg/L, respectively. The relative standard deviations (RSDs) of the retention times and peak areas were less than 0.09% and 0.49%, respectively. The recoveries of the three analytes were between 90.6% and 100.8%. The analytical results showed that GL and DCA were present in high concentration and no MCA was found when the proposed ion chromatography method was applied to three synthetical betaine samples. The proposed method is simple, sensitive and timesaving, and is also suitable for routine analysis in quality control of synthetical betaine products.     

Electrocatalytic dechlorination of chloroacetic acids by silver nanoparticles modified glassy carbon electrode

A simple potentiostatic method was employed to prepare silver nanoparticles deposited on glassy carbon electrode. The silver nanoparticles exhibit extraordinary electrocatalytic activities toward the reduction process of chloroacetic acids. The electrochemical behavior of trichloroacetic acid, dichloroacetic acid, and monochloroacetic acid has been investigated by cyclic voltammetry at the silver nanoparticles-modified glassy carbon electrode in 0.1 M LiClO₄ solution; each compound exhibits a series of reduction peaks which represent sequential dechlorination steps up to acetic acid. The electrocatalytic dechlorination mechanism for chloroacetic acids was also discussed in this work.     

Study on the interaction between nucleic acid and Eu3+-oxolinic acid and the determination of nucleic acid using the resonance light scattering technique

At pH 9.75, the resonance light scattering (RLS) intensity of OA–Eu³⁺ system is greatly enhanced by nucleic acid. Based on this phenomenon, a new quantitative method for nucleic acid in aqueous solution has been developed. Under the optimum condition, the enhanced RLS is proportional to the concentration of nucleic acid in the range of 1.0 × 10⁻⁹ to 1.0 × 10⁻⁶ g/ml for herring sperm DNA, 8.0 × 10⁻¹⁰ to 1.0 × 10⁻⁶ g/ml for calf thymus DNA and 1.0 × 10⁻⁹ to 1.0 × 10⁻⁶ g/ml for yeast RNA, and their detection limits are 0.020, 0.011 and 0.010 ng/ml, respectively. Synthetic samples and actual samples were satisfactorily determined. In addition, the interaction mechanism between nucleic acid and OA–Eu³⁺ is also investigated.     

A Simple Gas Chromatographic Method for the Measurement of Dichloroacetic Acid in Plasma or Urine

Abstract

A method has been developed for measurement of dichloroacetic acid in plasma or urine. The procedure is based on derivatization of dichloroacetic acid with methanol-boron trifluoride, extraction of the resulting methyl ester and gas chromatography. The method has good accuracy and precision, and can be used to determine concentrations as low as 0.04 μg/ml.     

Acid–Base Interactions in the Dichloroacetic Acid–N,N-Dimethylformamide System as Found from IR Spectroscopic Data

Ion–molecule interactions in the dichloroacetic acid–N,N-dimethylformamide system in the concentration range from pure acid to pure base at 30°C were investigated by multiple attenuated total internal reflectance IR spectroscopy. It was found that, depending on the ratio between components in solution, 1 : 1 or 2 : 1 acid–base complexes with strong hydrogen bonds are formed. With an excess of the acid, protonation of the base does not occur. The intensity of continuous absorption at 2000 cm^–1 is characteristic of quasi-ionic pairs with strong symmetrical hydrogen bonds. However, along with a continuous component, the spectra exhibited individual sharp peaks, which are typical of molecular complexes.     

Darzens synthesis of 2,2-dichloro-3-(2-furyl)-3-hydroxypropionic acid derivatives

Esters and amides of 2,2-dichloro-3-(2-furyl)-3-hydroxypropionic acid were prepared by the reaction of furfural with dichloroacetic acid derivatives under the conditions of the Darzens condensation. The structures of the reaction products were confirmed by their¹H NMR and IR spectra and chemical transformations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1444–1448, August, 1994.     

Analysis of Zoledronic Acid and Its Related Substances by Ion-Pair RP-LC

A simple high-performance liquid chromatographic method – ion-pair reversed- phase high performance liquid chromatography (RPIC) has been developed and employed for the analysis of zoledronic acid and its related substances in bulk material and commercial dosage forms. The mobile phase was a mixture of methanol (20%) and 5 mmol L^–1 phosphate buffer (80%) containing 6 mmol L^–1 tetrabutylammonium bromide, adjusted to pH 7.0 with sodium hydroxide. C₈ column was used as the stationary phase. The chromatographic conditions were optimized. The active ingredient – zoledronic acid was successfully separated from its related substances, including remained imidazol-1-yiacetic acid in the synthesis of zoledronic acid and other possible impurities of oxidation and decomposition. The excipients did not interfere with the determination of zoledronic acid in commercial dosage formulations. The method was rapid, simple, accurate and reproducible. It was not only successfully employed for the assay of zoledronic acid in bulk material and pharmaceutical dosage forms but also for the determination of its related substances.     

Determination of mono- and dichloroacetic acids in betaine media by liquid chromatography

A simple and sensitive method has been developed for the analysis of residue amounts of chloroacetic acids in betaine samples based on derivatization by 1-naphthylamine (NA). The derivatized compounds are analyzed by reverse phase high performance liquid chromatography using methanol and water as mobile phase in the ratio of 32/68 (v/v) and phenyl column and PDA detection at 222 nm. The detection limits (LOD) of monochloroacetic acid (MCA) and dichloroacetic acid (DCA) are 0.1 and 0.15 μg mL⁻¹, respectively. The limits of quantification (LOQ) and the linear dynamic ranges (LDR) of MCA are found to be 1 and 1-400 μg mL⁻¹, respectively, and for DCA are found to be 3 and 3-400 μg mL⁻¹, respectively. The precision at the 5 ppm level for MCA and DCA are about 3% and 2%, (n = 5), respectively. The average recovery for MCA and DCA spiked to betaine samples are 98% and 97%, respectively.     

Vacancy ion-exclusion chromatography of haloacetic acids on a weakly acidic cation-exchange resin

A new and simple approach is described for the determination of the haloacetic acids (such as mono-, di- and trichloroacetic acids) usually found in drinking water as chlorination by-products after disinfection processes and acetic acid. The new approach, termed vacancy ion-exclusion chromatography, is based on an ion-exclusion mechanism but using the sample solution as the mobile phase, pure water as the injected sample, and a weakly acidic cation-exchange resin column (TSKgel OApak-A) as the stationary phase. The addition of sulfuric acid to the mobile phase results in highly sensitive conductivity detection with sharp and well-shaped peaks, leading to excellent and efficient separations. The elution order was sulfuric acid, dichloroacetic acid, monochloroacetic acid, trichloroacetic acid, and acetic acid. The separation of these acids depends on their pKa values. Acids with lower pKa values were eluted earlier than those with higher pKa, except for trichloroacetic acid due to a hydrophobic-adsorption effect occurring as a side-effect of vacancy ion-exclusion chromatography. The detection limits of these acids in the present study with conductivity detection were 3.4 microM for monochloroacetic acid, 0.86 microM for dichloroacetic acid and 0.15 microM for trichloroacetic acid.     

A Sensitive Method for Determination Glycolic Acid, Mono- and Di-Chloroacetic Acids in Betaine Media Using Amino-Functionalized SBA-15 as a Sorbent and HPLC Assay

In this paper, amino-modified nanoporous silica (APS-SBA-15) was synthesized as a new solid-phase sorbent for the extraction of glycolic acid, monochloroacetic acid, and dichloroacetic acid in synthetical betaine products. Octadecyl silica cartridge was used to reduce the concentration of matrix betaine. PS-Ag⁺ pre-treatment cartridge was applied to remove high Cl^? concentration. The obtained effluent sample was passed through of the APS-SBA-15 sorbent. The effect of pH, flow rate of sample and eluent, and type and volume of the eluent were investigated and optimized. Chloroacetate and glycolate were eluted with 0.8 mol L^?1 solution of HClO₄ and measured by HPLC with a UV–vis detector. At optimum effective parameters, preconcentration factor of 129 was achieved in this method. The detection limits of mono- and dichloroacetic acid and glycolic acid were 13, 3.7, and 8.6 ng L^?1, respectively.     

An investigation of the chemiluminescence reaction in the sodium hypochlorite–folic acid–emicarbazide hydrochloride system

A chemiluminescence method for the determination of folic acid by the sodium hypochlorite–folic acid–semicarbazide hydrochloride system with a new flow injection technique has been established. The new method can perform simple, sensitive and rapid determinations of folic acid. The response to the concentration of folic acid, in the range of 1.0×10⁻⁷5.0×10⁻⁵ g/ml, is linear. The relative standard deviation of the method is 2.3% (C_s=4.0×10⁻⁶ g/ml, n=11). The detection limit is 2.7×10⁻⁸ g/ml. This method is suitable for automatic and continuous analysis, and has been successfully tested for the determination of folic acid in a folic acid tablet.     

Determination of Dopamine in the Presence of Ascorbic Acid Using a Poly(Amidosulfonic Acid) Modified Glassy Carbon Electrode

A glassy carbon electrode (GCE) was modified with electropolymerized films of amidosulfonic acid in pH 7.0 phosphate buffer solution (PBS) by cyclic voltammetry (CV). The modified electrode showed an excellent electrocatalytical effect on the oxidation of dopamine (DA). In pH 7.0 PBS, the anodic peak current increased linearly with the concentration of DA in the range of 5.0×10^–7 1.0×10^–4moldm^–3, with a correlation coefficient of 0.9932, and a detection limit (S/N=3) of 1.0× 10^–7moldm^–3. The relative standard deviation of 10 successive scans was 2.5% for 1.0×10^–6moldm^–3 DA. The interference of ascorbic acid (AA) with the determination of DA could be eliminated because of the very distinct attracting interaction between DA cations and the negatively poly(amidosulfonic acid) film in pH 7.0 PBS. The proposed method exhibited good recovery and reproducibility.     

离子色谱法测定饮用水中的5种卤代乙酸

利用IonPac AS19大容量阴离子交换色谱柱对水中的一氯乙酸、二氯乙酸、三氯乙酸、一溴乙酸、二溴乙酸5种卤代乙酸(HAAs)进行了分离,优化了分离条件.通过控制分离温度实现了二氯乙酸(DCAA)与NO2-的分离;通过梯度洗脱使三氯乙酸(TCAA)与SO42-得到较好、较快的分离;通过中和脱气法解决了在大量CO32-(HCO3-)存在时对实验的干扰.DCAA、TCAA的检出限(以3倍信噪比计)分别达到了2.50 μg/L和3.75 μg/L.5种HAAs在10.0～2 000.0 μg/L线性范围内线性相关系数在0.999以上.