Spectrophotometric determination of trace water in organic solvents with a near infrared absorbing dye

A spectrophotometric method for the determination of trace water in organic solvents using a near infrared absorbing dye has been developed. This method is based on the effect that a minor change in polarity of the solvent caused by trace water content determines the extent of aggregation of a near-infrared dye monomer. This change can be detected spectrophotometrically. The calibration curves for methanol, ethanol, and isopropanol were determined. This method has the highest sensitivity (em = 16.73 unit) for water in isopropanol and the lowest sensitivity (em = 2.806 unit) for water in methanol. The correlation coefficient (R)(2) values for the regression lines ranges from 0.990-0.998. The linear range of the method for ethanol is 0.001-0.5%, for isopropanol is 0.001-0.1%, and for methanol is 0.001-1.0%. The limit of detection for ethanol, isopropanol, and methanol are 0.0001, 0.0001, and 0.005% water, respectively. The developed method is sensitive, simple and easy to operate, and the cost of analysis is low.     

化妆品中挥发性有机溶剂的通用检测方法

以化妆品配方中常见及禁用的36种有机溶剂为研究模板,建立了化妆品中挥发性有机溶剂残留评价初筛知识库、确证知识库和定量方法。初筛知识库包括双柱保留指数知识库和NIST质谱库。双柱保留指数知识库以保留指数为定性指标,选择极性的VF-1301ms和非极性的DB-5ms两根色谱柱,用顶空气相色谱-质谱法考察了36种有机溶剂在两种色谱分离系统中的保留特性。利用NIST MS search 2.0作为检索工具,同时建立了36种挥发性有机溶剂的顶空气相色谱-质谱定量方法。样品经60 ℃、30 min静态顶空后以连接了VF-1301ms石英毛细管色谱柱的气相色谱-质谱仪检测,外标法定量。方法检出限为0.01~3.3 μg/g,加标回收率为60.77%~126.60%。该方法从通用性的角度,为化妆品中挥发性有机溶剂残留的筛查、鉴别和定量提供方法,部分解决了测定化妆品中挥发性有机溶剂时需要针对不同检测目标建立不同方法以及潜在溶剂存在备选筛查的问题。     

Vortex‐assisted natural deep eutectic solvent microextraction using response surface methodology optimization for determination of orthophosphate in water samples by molybdenum blue method

A new, rapid, and efficient microextraction technique named vortex‐assisted natural deep eutectic solvent microextraction has been developed for the preconcentration and determination of orthophosphate in real water samples. The method is based on the formation of the phosphomolybdenium blue complex followed by proposed microextraction procedure and subsequent spectrophotometric determination in a microcell. Screening study for the optimal composition of natural deep eutectic solvent was initially performed with different solvents, including choline chloride as hydrogen bond acceptor and different hydrogen bond donors. A ternary mixture of glucose‐choline chloride‐water was used as the most efficient extraction solvent. Response surface methodology based on the central composite design was used to optimize experimental parameters. Under optimal conditions, the calibration graph for orthophosphate determination was linear over the range of 2.0–80.0 µg/L (correlation coefficient of 0.9971) with a detection limit of 0.2 µg/L. The repeatability, reproducibility, and relative error values of the method were below 7%, indicating acceptable precision and accuracy. This approach, using natural deep eutectic solvent as an eco‐friendly solvent with high solubilization power and vortex mixing as an alternative energy source, represents a promising choice for a green separation and preconcentration methodology for determination of orthophosphate in real water samples.     

基于轻质萃取剂的溶剂去乳化分散液-液微萃取-气相色谱法测定水样中多环芳烃

以密度小于水的轻质溶剂为萃取剂,建立了无需离心步骤的溶剂去乳化分散液-液微萃取-气相色谱(SD-DLLME-GC)测定水样中多环芳烃的新方法。传统分散液-液微萃取技术一般采用密度大于水的有机溶剂为萃取剂,并需要通过离心步骤促进分相。而本方法以密度比水小的轻质溶剂甲苯为萃取剂,将其与丙酮(分散剂)混合并快速注入水样,获得雾化体系;然后注入乙腈作为去乳化剂,破坏该雾化体系,无需离心,溶液立即澄清、分相;取上层有机相(甲苯)进行GC分析。考察了萃取剂、分散剂、去乳化剂的种类及其体积等因素对萃取率的影响。以40 μL甲苯为萃取剂,500 μL丙酮为分散剂,800 μL乙腈为去乳化剂,方法在20～500 μg/L范围内呈现出良好的线性(r2=0.9942～0.9999),多环芳烃的检出限(S/N=3)为0.52～5.11 μg/L。用所建立的方法平行测定5份质量浓度为40 μg/L的多环芳烃标准水样,其含量的相对标准偏差为2.2%～13.6%。本法已成功用于实际水样中多环芳烃的分析,并测得其加标回收率为80.2%～115.1%。     

Determination of Surfactants Using Ion Pair Extraction of Near-infrared Laser Dyes

Abstract

Ionic surfactants and near-infrared laser dyes formed complexes which were extracted into organic solvents as ion pairs. Surfactants were determined spectrophotometrically by measuring the near-infrared absorbance and fluorescence of the ion pair in the organic solvent. Several of the commercially available near infrared dyes have been found suitable for surfactant determination in water using this technique. The excess near-infrared dye coextracted into the organic solvent was determined by blank extractions. The calibration curves were linear within two orders of magnitude of surfactant concentrations. Non-linear calibration curves are obtained for wider concentration range of surfactants. This method using the recently developed near-infrared laser diode intracavity technique was applied to the determination of SDS in water. Lower detection limits and ease of operation are the major advantages of using this new laser diode technique. The extraction efficiency of different solvent systems was evaluated.     

Further development of catalase, tyrosinase and glucose oxidase based organic phase enzyme electrode response as a function of organic solvent properties

Using three enzyme sensors (tyrosinase, catalase and glucose oxidase), capable of functioning also in non-aqueous solvents, we found new correlations between classical indicators, e.g. the log P value of several organic solvents and new empirical indicators such as ;maximum current variation' (MCV) and above all the ;current variation rate' (CVR), the values of which may be monitored with the biosensor considered dipping directly into the organic solvent. The trend of the immobilised specific activity of the tyrosinase enzyme dipping into different organic solvents was evaluated and compared with that determined by the spectrophotometric method. Lastly, an investigation was performed to experimentally verify the relation between hydrophobicity of the solvent and its ability to draw back the water from the enzyme microenvironment using the Karl Fischer method and thermogravimetric analysis to estimate the residual water in the enzyme microenvironment after having treated the enzyme with the organic solvent, then allowing it to dry.     

A novel approach in dispersive liquid-liquid microextraction based on the use of an auxiliary solvent for adjustment of density: UV-VIS spectrophotometric and graphite furnace atomic absorption spectrometric determination of gold based on ion pair formation

This paper presents a novel approach to dispersive liquid-liquid microextraction (DLLME), based on the use of an auxiliary solvent for the adjustment of density. The procedure utilises a solvent system consisting of a dispersive solvent, an extraction solvent and an auxiliary solvent, which allows for the use of solvents having a density lower than that of water as an extraction solvent while preserving simple phase separation by centrifugation. The suggested approach could be an alternative to procedures described in the literature in recent months and which have been devoted to solving the same problem. The efficiency of the suggested approach is demonstrated through the determination of gold based on the formation of the ion pair [Au(CN)₂]⁻ anion with Astra Phloxine (R) reagent and its extraction using the DLLME procedure with subsequent UV-VIS spectrophotometric and graphite furnace atomic absorption spectrometric detection. The optimum conditions were found to be: pH 3; 0.8 mmol L⁻¹ K₄[Fe(CN)₆]; 0.12 mmol L⁻¹ R; dispersive solvent, methanol; extraction solvent, toluene; auxiliary solvent, tetrachloromethane. The calibration plots were linear in the ranges 0.39-4.7 mg L⁻¹ and 0.5-39.4 μg L⁻¹ for UV-VIS and GFAAS detection, respectively; thus enables the application of the developed method in two ranges differing from one from another by three orders of magnitude. The presented approach can be applied to the development of DLLME procedures for the determination of other compounds extractable by organic solvents with a density lower than that of water.     

A comparison of various modes of liquid–liquid based microextraction techniques: Determination of picric acid

Three modes of liquid–liquid based microextraction techniques – namely auxiliary solvent‐assisted dispersive liquid–liquid microextraction, auxiliary solvent‐assisted dispersive liquid–liquid microextraction with low‐solvent consumption, and ultrasound‐assisted emulsification microextraction – were compared. Picric acid was used as the model analyte. The determination is based on the reaction of picric acid with Astra Phloxine reagent to produce an ion associate easily extractable by various organic solvents, followed by spectrophotometric detection at 558 nm. Each of the compared procedures has both advantages and disadvantages. The main benefit of ultrasound‐assisted emulsification microextraction is that no hazardous chlorinated extraction solvents and no dispersive solvent are necessary. Therefore, this procedure was selected for validation. Under optimized experimental conditions (pH 3, 7 × 10^?5 mol/L of Astra Phloxine, and 100 μL of toluene), the calibration plot was linear in the range of 0.02–0.14 mg/L and the LOD was 7 μg/L of picric acid. The developed procedure was applied to the analysis of spiked water samples.     

Potentiometric determination of the dissociation constants of L-histidine, proline and tryptophane in various hydroorganic media

The dissociation constant values of L-histidine, proline and tryptophane were determined at 25 +/- 0.1 degrees C by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, acetone and dioxane. Initial estimates of the dissociation constant values of the different amino acids studied have been refined with ESAP2M computer program. It was observed that changing the medium permittivity as the solvent is enriched in methanol or ethanol has little influence on the pK*(a) values of the amino acids studied. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents and the possible variation in microheterogeneity of the salvation shells around the solute.     

Development of a new and environment friendly hollow fiber-supported liquid phase microextraction using vesicular aggregate-based supramolecular solvent

Hollow fiber-based liquid phase microextraction (HF-LPME) using conventional solvents is limited by their relative instability and high volatility. The use of supramolecular solvents as a liquid membrane phase could overcome these inconveniences due to their negligible vapour pressure and high viscosity. In the present study, a novel and highly flexible method was developed based on supramolecular solvents constructed of vesicles of decanoic acid, which were used for the first time as a solvent in HF-LPME. This solvent is produced from the coacervation of decanoic acid aqueous vesicles by the action of tetrabutylammonium (Bu(4)N(+)). In this work, halogenated anilines as model compounds were extracted from water samples into a supramolecular solvent impregnated in the pores and also filled inside the porous polypropylene hollow fiber membrane. The extracted anilines were separated and determined by high-performance liquid chromatography. The technique requires minimal sample preparation time and toxic organic solvent consumption, and provides a significant advantage over conventional analytical methods. The important parameters influencing the extraction efficiency were studied and optimized utilizing two different optimization methods: one variable at a time and the Box-Behnken design. Under the optimum conditions, the preconcentration factors were in the range of 74 to 203. Linearity of the method was obtained in the range of 1.0-100 μg L(-1) with the correlation coefficients of determination (R(2)) ranging from 0.9901 to 0.9986. The limits of detection for the target anilines were 0.5-1.0 μg L(-1). The relative standard deviations varied from 3.9% to 6.0%. The relative recoveries of the three halogenated anilines from water samples at a spiking level of 20.0 μg L(-1) were in the range of 90.4-107.4%.     

A novel ferroin membrane sensor for potentiometric determination of iron

A novel potentiometric approach for both batch and flow injection determination of iron(II) and/or iron(III) is described. It is based on the formation and monitoring of ferroin with a PVC membrane sensor containing ferroin-TPB as an electroactive component plasticized with 2-nitrophenyl phenyl ether. The sensor exhibits fast Nernstian response for ferroin with a cationic calibration slope of 30 +/- 0.2 mV/concentration decade down to 4 x 10(-7)M ferroin (0.03 ppm Fe) at pH 3-9. Interferences from common inorganic cations are negligible or can be eliminated by a pretreatment with DDC. The ferroin sensor was successfully applied to the determination of iron contents in water, alloys, rocks and pharmaceuticals. The results show good correlation with data obtained by the standard spectrophotometric ferroin method, the coefficient of correlation is better than 0.7%.     

FIA titrations of phenothiazine derivatives in aqueous micellar and non-aqueous media

New methods of flow injection analysis (FIA) neutralization titrations of phenothiazine derivatives in aqueous micellar medium of a cationic surfactant using potentiometric and spectrophotometric detection were proposed; titrations with a mixing gradient chamber and high-speed titrations were compared. The FIA titration method in non-aqueous media based on an official method of determination (titration with perchloric acid in anhydrous acetic acid) was also developed. Under optimized reaction conditions and flow-through parameters, the calibration range and equations, the sensitivity, and the repeatability of all methods were found and discussed. All titrations were assayed for medicinal forms.     

有机溶剂中微量水分的测定

绕丹宁与水在有机溶剂中发生诱导荷移反应,产生吸收光谱移动且吸收峰增大。基于此,优化了实验条件,建立了一种快速、简便、灵敏的测定有机溶剂中微量水分的新方法。甲醇、醋酸溶剂中的水分含量分别在3％-10％（φ）、0～4％（φ）范围及乙醇、1-丙醇、丙酮、乙酸乙酯溶剂中水分含量在0～5％（φ）范围内与吸光度（A）呈线性关系。其相关系数分别是0．9992、0．9996、0．9992、0．9982、0．9990和0．9995。使用本方法测定了灯用酒精中水分含量,结果令人满意。     

The Acidity and Solvation of Lignin-Related Phenols in Water—1,4-Dioxane Mixtures

The pK _a values were determined for 10 guaiacyl phenols by UV spectrophotometric and potentiometric titration in the water—dioxane binary system over the composition range 0–80% organic solvent. The differentiating action of the solvent and para-substituent effects on the acidity of guaiacol derivatives were analyzed. The dependences of acidity constants on the mixed solvent composition were interpreted using the preferential solvation model.     

Influence of solvent properties on separation and detection performance in non-aqueous capillary electrophoresis-mass spectrometry of basic analytes

The versatility of non-aqueous capillary electrophoresis (NACE) results mainly from the variety of physico-chemical properties of the different solvents. They provide solubility for a wide range of analytes, enable to control electrophoretic selectivity, but affect in some cases UV absorbance detection. The coupling of NACE to electrospray mass spectrometry (ESI-MS) allows to cope with the high UV cut-off of some CE relevant solvents (e.g., formamides). In this paper the pure organic solvents methanol, acetonitrile, dimethylsulfoxide, formamide, N-methylformamide and N,N-dimethylformamide are evaluated against water for the preparation of ammonium acetate electrolytes to separate the basic model substances 2-aminobenzimidazole, procaine, propranolol and quinine with NACE-MS. MS coupling is assisted with the sheath liquid water-isopropanol (1:4, v/v) with 0.1% formic acid. The goal of the paper is to assess the influence of the solvent on selectivity, separation speed, and peak efficiency for a given set of model compounds on a simple empirical basis. It should give the user an idea how the separation quality is changed when nothing but the running solvent is altered. The obtained efficiency results were discussed with respect to physico-chemical models described in literature (assuming longitudinal diffusion as the only source of band broadening), but no satisfying correlations with solvent properties could be traced. The feasibility of all six organic solvents for MS coupling was demonstrated and the influence of the separation solvent on the MS detection performance was compared. In the seven different solvents, the shortest run time was obtained with acetonitrile, the best peak resolution with the amphiprotic solvents (especially methanol) best peak efficiency with methanol and formamide, and the most sensitive ESI-MS detection with acetonitrile and methanol, but with only slight advantage to water.     

Flow injection spectrophotometric determination of boron in ceramic materials

A flow injection spectrophotometric method for the determination of boron in ceramic materials is described. The method is based on spectrophotometric measurement of the decrease in the pH produced by the reaction between boric acid and mannitol in the presence of an acid-base indicator. A bichannel FI (flow injection) manifold in which the sample solutions were injected into deionized water (at pH 5.4) and the stream was later merged with the reagent stream (a mannitol solution containing 1x10(-4) mol l(-1) bromocresol green at pH 5.4), was used. Transient signals were monitored at 616 nm. A theoretical model which describes the dependence between the absorbance values and boric acid concentration is presented. The model predicts a non linear dependence between the absorbance or increment in absorbance and the boric acid concentration. In contrast, the model predicts a linear dependence between the inverse of the absorbance values and the boric acid concentration. The calibration graphs (1/A vs mug ml(-1) B(2)O(3)) were linear over the range 1-30 mug ml(-1) of B(2)O(3). The relative standard deviations were 0.7 and 0.4% for 4 and 8 mug ml(-1) of B(2)O(3), respectively. The limit of detection was 0.02 mug ml(-1) of B(2)O(3) (3sigma criterium). The method was used to determine boron in nine ceramic materials with very different nominal boron compositions. The results were compared with those obtained using a potentiometric titration method as reference method. No significant differences (at 95% probability level) were found between the proposed and reference methods. The method is rapid, reliable, precise and free of interferences.     

Application of a micro multiphase laminar flow on a microchip for extraction and determination of derivatized carbamate pesticides.

Determination of carbamate pesticides such as carbaryl, carbofuran, propoxur and bendiocarb was demonstrated on a microchip with newly designed microchannels developed for efficient solvent extraction. The pesticides were hydrolyzed to corresponding naphthols, coupled with p-nitrobenzenediazonium fluoroborate reagent, and then extracted into 1-butanol as colored azo derivatives and detected with a thermal lens microscope. Optimum flow rates for the aqueous and organic phases were evaluated in the continuous-flow chemical process established in the microchip. The calibration lines showed good linearity in the range of concentrations of 0.03 - 3 ppm (10(-7) - 10(-5) M) and a mass detection limit down to a nanogram level was achieved that is at least two orders of magnitude lower than the LODs for conventional spectrophotometric methods. Azo derivatives of the pesticides were successfully separated and identified by micellar electrokinetic chromatography (MEKC) using a sample prepared on a bulk scale.     

Ionization constants for water and for very weak organic acids in aqueous organic mixtures

A potentiometric method using a glass electrode has been applied to the determination of apparent ionization constants for water in binary mixtures of water with 11 organic solvents at 25°C. Further calculations with these apparent ionization constants permit evaluation of the acid ionization constant for some of the organic solvents as solutes in purely aqueous solvent by two different methods. Resulting values of pK _a derived from this work are: 1,2-propanediol (14.8 and 14.8), 2,3-butanediol (15.0 and 14.7), 1,3-butanediol (15.5 and 14.8), 1,4-butanediol (14.5 and 14.4), 2-butene-1,4-diol (14.0 and 13.9), 2-butyne-1,4-diol (12.1 and 12.4), 2-methoxyethanol (15.2 and 14.8), 2-ethoxyethanol (15.0 and 14.5), and triethylene glycol (14.6 and 14.3). None of the 11 solvents shows appreciable basicity.     

Determination of water by flow-injection analysis with the karl fischer reagent

A method for the determination of water in organic solvents by flow-injection analysis (f.i.a.) is described. The method, which is based on the reaction between water and the Karl Fischer reagent, is capable of 120 determinations per hour. The concentration range 0.01–5% (v/v) of water can be covered by using a single Karl Fischer reagent solution. The results obtained with a specially constructed potentiometric detector showed a relative standard deviation of less than 0.5% (v/v). This value was about 3 times less than that obtained with a spectrophotometric detector. The f.i.a. technique is shown to offer some unique possibilities in minimizing interferences associated with the standard Karl Fischer batch titration method.     

Studies on the Effect of Organic Solvents and Temperature on the Micellar Solution of Pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) Gemini Surfactant

Effects of three organic solvents, viz. methyl cellosolve, acetonitrile, and formamide, on the micellization process of Gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) aqueous solutions, with the volume percentages of the organic solvents up to 50%, have been investigated conductometrically. The studies were made at different temperatures and the data were used to find out different micellization parameters. From the study, it was observed that, although an increment in the amount of the organic solvents delays the micellization, the increase in the critical micelle concentration (cmc) is comparatively less below 20%(v/v) showing the predominance of water character in the bulk phase at lower compositions of the organic solvents. Applying equilibrium model for micelle formation, various thermodynamic parameters were also calculated from the temperature dependence of the cmc values and the results show that the micellization process becomes less spontaneous as the volume % of the organic solvent increases in the system due to the action of water-organic solvent mixed media as better solvent than pure water (solvophobic effect) for the studied Gemini molecules.