Membraneless vaporization unit for direct analysis of solid sample.

A new apparatus, called 'membraneless vaporization' (MBL-VP) unit was designed and developed for direct analysis of solid samples. Solid analyte was converted into a gaseous form which then reacts with an indicator reagent. Change in absorbance was used to quantitate the analyte. Stirring with a magnetic bar was employed to facilitate the evaporation of the gas. Unlike the pervaporation technique, hydrophobic membrane was not required for this MBL-VP technique. Application of the membraneless technique for direct determination of calcium carbonate in calcium supplements, has shown to be very precise (R.S.D.=2.5% for 0.16 mmol CO3(2-)), with detection limit of 0.5 mg CaCO3. Results by this method agreed well with flame atomic absorption spectrometric method. Sample throughput was 20 samples h(-1).

Novel catalytic oxidative coupling reaction of N,N-dimethyl-p-phenylenediamine with 1,3-phenylenediamine and its applications to the determination of copper and iron at trace levels by flow injection technique.

A new catalytic oxidative coupling reaction of N,N-dimethyl-p-phenylenediamine (DPD) with 1,3-phenylenediamine (mPD) in the presence of hydrogen peroxide has been developed for trace metals analysis. The rate of the oxidation/coupling reaction can be enhanced significantly by iron, copper and cobalt. These metal ions can catalyze the oxidation reaction of DPD to form an oxidized product; the oxidized DPD was then coupled with mPD to give a blue-colored product which was measured spectrophotometrically at 650 nm. On the basis of such a reaction scheme, two simple flow injection analysis methods for the determination of copper and iron have been developed. Detailed studies on chemical and FIA variables affecting the sensitivity of the detection were carried out. Interferences from several ionic species were examined for the determination of copper: the interference effect by Fe(III) and Fe(II) up to 1.5 mg L(-1) was successfully suppressed by pretreating sample with ammonium acetate buffer solution (pH 8.4). Good linearity of a standard calibration graph was obtained over the ranges of 0-8 and 0-2 microg L(-1) of copper and iron, respectively, and the detection limits were 0.05 and 0.02 microg L(-1) for copper and iron, respectively. The precision of the methods in terms of relative standard deviation were 1.4 and 1.5% of R.S.D. which were obtained from 10 injections of 2.0 and 1.0 microg L(-1) of standard copper and iron, respectively. The proposed methods were successfully applied to the determination of copper and iron in tap and river water samples. The accuracy of the proposed methods was assessed by the analysis of certified reference material of river water.

A membraneless gas diffusion unit: design and its application to determination of ethanol in liquors by spectrophotometric flow injection.

This work presents new design of a gas diffusion unit, called 'membraneless gas diffusion (MGD) unit', which, unlike a conventional gas diffusion (GD) unit, allows selective detection of volatile compounds to be made without the need of a hydrophobic membrane. A flow injection method was developed employing the MGD unit to determine ethanol in alcoholic drinks based on the reduction of dichromate by ethanol vapor. Results clearly demonstrated that the MGD unit was suitable for determination of ethanol in beer, wine and distilled liquors. Detection limit (3S/N) of MGD unit was lower than the GD unit (GD: 0.68%, v/v; MGD: 0.27%, v/v). The MGD design makes the system more sensitive as mass transfer is more efficient than that of GD and thus, MGD can perfectly replace membrane-based designs.

Determination of total and dissolved amount of iron in water samples using catalytic spectrophotometric flow injection analysis.

A flow injection spectrophotometric method has been developed for the determination of dissolved and total amounts of iron in tap and natural water samples. The method for the determination of iron employs a sample acidification step in order to decompose iron hydroxide and iron-complexes into free iron, Fe(III) and Fe(II). The amounts of free iron were detected using a catalytic action of Fe(III) and Fe(II) on the oxidation of N,N-dimethyl-p-phenylenediamine in the presence of hydrogen peroxide. Increase in absorbance of oxidized product was detected spectrophotometrically at 514 nm. The proposed method allows 0.02 and 0.06 microg l(-1) of LOD and LOQ, respectively, with relative standard deviation (RSD) below 2%. The accuracy and the precision of the method were evaluated by the analysis of the standard reference material, river water. The developed method was successfully applied to real water samples.

Determination of trace amounts of bromide by flow injection/stopped-flow detection technique using kinetic-spectrophotometric method.

A simple, sensitive and selective method for the determination of bromide in seawater by using a flow injection/stopped-flow detection technique was examined. The detection system was developed for a new kinetic-spectrophotometric determination of bromide in the presence of chloride matrix without any extraction and/or separation. The detection was based on the kinetic effect of bromide on the oxidation of methylene blue (MB) with hydrogen peroxide in a strongly acidic solution. Large amounts of chloride could enhance the sensitivity of the method as an activator. The decolorisation of the blue color of MB was used for the spectrophotometric determination of bromide at 746nm. A stopped-flow approach was used to improve the sensitivity of the measurement and provide good linearity of the calibration over the range of 0-3.2mugml(-1) of bromide. The relative standard deviation was 0.74% for the determination of 2.4mugml(-1) bromide (n=5). The detection limit (3sigma) was 0.1mugml(-1) with a sampling frequency of 12h(-1). The influence of potential interfering ions was studied. The proposed method was applied to the determination of bromide in seawater samples and provided satisfactory results.

Analysis of complex formation between crown ethers and potassium ion by determining retention factors in reversed-phase high-performance liquid chromatography.

Retention factors in reversed-phase high-performance liquid chromatography (RP-HPLC) were utilized for the analysis of complex formation reaction of four crown ethers with potassium ion in water-methanol media. The crown ethers were injected as analytes, potassium ion was present in the eluent, and three types of reversed-phase columns were used. The retention factor of the crown ethers decreased with increasing concentrations of potassium ion in the eluent, which is attributed to the change in the species of the crown ether from a neutral ligand to a positively charged complex. The complex formation constants were determined by analyzing the changes in the retention factor with a non-linear least-squares method.

Highly sensitive determination method for total carbonate in water samples by flow injection analysis coupled with gas-diffusion separation.

A spectrophotometric method for the determination of total carbonate in water samples was developed. The method is based on the color change of an acid-base indicator in relation to the concentration of permeable gas substances through a membrane. By using a new portable FIA system equipped with a gas-diffusion unit, a highly sensitive and on-site determination of total carbonate in aqueous solutions was investigated. A new color-change system with 4-(2',4'-dinitrophenylazo)-1-naphthol-5-sulfonic acid (DNN5S) was developed. Absorbance changes of the reagent solution were measured at 450 nm with a light-emitting diode (LED) as a light source. A new type of gas-diffusion unit was used, and was constructed with double tubing: the inner tubing was a micro porous PTFE (polytetrafluoroethylene) tubing (1.0 mm inner diameter and 1.8 mm outer diameter, pore size 2 microns, porosity 50%); the outer tubing was made of glass with 2.0 mm inner diameter. The optimized system conditions were as follows: the sample size was 200 microliters, the temperature of the air bath for the gas-diffusion unit was 25 degrees C, and the length of the gas-diffusion unit was 15 cm; each flow rate was 0.3 ml min-1. For measuring carbonate at low concentrations, a method for preparing water with less carbonate was proposed: the carbonate content of the water was decreased down to 5 x 10(-7) M. The calibration graph was rectilinear from 1 x 10(-6) M to 10(-3) M, and the detection limit (corresponding to a signal-to-noise ratio of 3) was 1 x 10(-6) M of carbonate. The relative standard deviation (RSD) of ten measurements of 2.3 x 10(-5) M Na2CO3 solution was 1.9%. The total carbonate in various kinds of water (such as river, sea, rain, distilled and ultra purified) was determined.

Complex formation analysis of water-soluble calixarenes by capillary zone electrophoresis.

The equilibria of complex formation reactions between various kinds of cations and anionic calixarenes in an aqueous solution were analyzed by capillary zone electrophoresis on the basis of the change in electrophoretic mobility of the calixarenes. The apparent electrophoretic mobility of the calixarenes decreased with increasing concentrations of alkali metal ions and quaternary ammonium ions. Equilibrium constants were determined by a non-liner least-squares analysis using the changes in apparent electrophoretic mobility. The complex formation constants obtained with alkali metal ions were in the order of 10(2.3) - 10(3.0), and those with quaternary ammonium ions were 10(2.9) - 10(4.2), providing less selectivity among them. The selectivity of the calixarene toward alkali metal and quaternary ammonium ions in aqueous solution involves flexible structure, and compensative interactions of electrostatic and hydrophobic interactions. From the results obtained in this work, the electrophoretic method has proved to be useful for analyzing the reactivity of anionic calixarene in aqueous solution.

Separation and determination of n-alkylamines and histamine by capillary zone electrophoresis using salicylaldehyde-5-sulfonate as a derivatizing reagent.

Sodium salicylaldehyde-5-sulfonate (SAS) was investigated as a derivatizing reagent for the separation and determination of primary amines by capillary zone electrophoresis (CZE). The amines were derivatized with SAS to the corresponding Schiff bases before their determination. Optimal conditions for the formation reactions of the Schiff bases and the CZE analysis were investigated in details. The Schiff bases were formed almost completely within 9 min in 40%(v/v) ethanol solution at 40 degrrees C. A migrating solution containing 40%(v/v) ethanol and 20 mM phosphate buffer (pH 7.8) was found to be preferable for the stability of the Schiff bases. Eight kinds of n-alkylamines were derivatized with SAS under the optimal conditions and the derivatives were successfully separated by a CZE analysis. The proposed method allows simultaneous, sensitive and sufficiently precise determination of the n-alkylamines with the alkyl chain length from 3 to 12 of methylene groups. The derivatization process with SAS was successfully applied to the detection of histamine at a very low level. The detection limit was 2.5-10(-6) M, and it was improved in the order of 8 times compared with the CZE analysis without derivatization.

Analysis of highly saline samples by capillary zone electrophoresis: enhanced direct UV detection of inorganic anions using on-capillary preconcentration and clean-up techniques.

The ability to analyze samples with disparate levels of analyte and matrix ions is among the important benefits defining the practical utility of modern capillary electrophoresis. To compensate for the sensitivity limitations regarding trace-level inorganic anions, a number of on-line approaches that should offer an improved S/N ratio in direct UV detection were examined. The novel use of reversed pre-electrophoresis (at the applied voltage opposite to the separation voltage) made it possible to efficiently remove the most part of high chloride levels from the sample and hence to lower the background signal and to inject increased quantities of fast analyte anions. Specifically, by taking these advantages the sensitivity response of iodide was improved by a factor of 5 over normal CE mode. Using isotachophoretic sample stacking, a two-fold increase in detectability was obtained for moderately mobile anions, nitrate and nitrite, that corresponds to the minimum detectable concentrations close to their natural occurrences in seawater. Furthermore, field-amplified sample injection at increased electrolyte-to-sample matrix concentration ratios enabled the maximum S/N enhancement, with detection limits at the level of 10(-6) M and lower in the presence of > or = 5 x 10(4)-fold molar excess of chloride.

Separation and determination of haloperidol, parabens and some of their degradation products by micellar electrokinetic chromatography.

A micellar solution containing phosphate buffer, anionic surfactant, and water-miscible organic solvent was employed as a migration solution for the separation and the quantification of eleven analytes by micellar electrokinetic chromatography (MEKC): the analytes examined were haloperidol, methylparaben, ethylparaben, n-propylparaben, iso-propylparaben, n-butylparaben, iso-butylparaben, sec-butylparaben, 4-(4-chlorophenyl)-4-hydroxypiperidine, 4-fluorobenzoic acid and 4-hydroxybenzoic acid. In order to provide good separation between micelle and haloperidol, which showed strongest interaction with the micelle among the analytes, surfactant concentrations and organic modifier percentages were studied with phosphate buffer at pH 7.0. All the analytes were successfully resolved when 10 mM sodium dodecylsulfate and 15% ethanol were contained in the migration solution; the time window was very wide in the range from 14.8 to 65.5 min. Optimized applied voltage at 30 kV and capillary temperature at 45 degrees C enable analyze all compounds in less than 17 min with the best resolution, the shorter migration time window, the highest precision and lowest detection limit.

Equilibrium analysis of reactions between aromatic anions and nonionic surfactant micelles by capillary zone electrophoresis.

Separability of some positional isomers of aromatic anions by capillary zone electrophoresis was improved by adding nonionic surfactants to a migrating solution. Eleven kinds of aromatic anions, including positional isomers, were used as analytes, and Brij-35, Brij-58 and Brij-78 were investigated as nonionic surfactants to form micelles, where hydrophobicities are different from each other. Increasing the concentration of the surfactants developed the separability of the anionic isomers. The interaction between the anions and the nonionic surfactant micelles is also investigated through the change in the electrophoretic mobility, and the binding constants are determined. Apparent electrophoretic mobility of the anions decreased with increasing concentrations of the nonionic surfactants. The decrease in the mobility, as well as the binding constant, was larger in the monovalent anions than in the divalent anions, which indicates that the interaction or reactivity of the monovalent analytes is higher than that of the divalent analytes. The reactivity of each anion was almost identical even when the kinds of the surfactants were changed, suggesting that the hydrophobicity of the polyoxyethylene group in the surfactant would have the main role for binding the analytes. The reactivity tendency among the positional isomers was almost similar to that in ion association-capillary zone electrophoresis using tertabutylammonium ion as a pairing ion. The results obtained in this work suggest that the anions are bound to the micelles by the hydrophobic interaction between analyte anions and the polyoxyethylene moiety of the surfactant micelles. Changes in the fluorescence intensity of the anions were also investigated; the results can explain well the mobility changes of the analytes.

Electrophoretic mobility study on ion-ion interactions in an aqueous solution.

Ion-ion interactions between anions and their pairing ions in aqueous solutions were studied through the measurements of electrophoretic mobilities of analyte ions in capillary zone electrophoresis, where the electrophoretic method for the analysis of ion association reaction is shown to be more useful than the conductometric method widely used in the analysis of the reactions. The electrophoretic mobility of monovalent inorganic anions was almost identical even when the concentrations of alkali metal ions and quaternary ammonium ions in the migrating solution were varied up to 15 mM. On the other hand, the electrophoretic mobility of organic anions, such as monovalent and divalent anions, decreased with increasing concentrations of quaternary ammonium ions. Changes in the electrophoretic mobilities were analyzed by a non-linear least-squares method giving ion association constants. The results indicate that the proposed method is applicable to the analysis of such reactions to give the mobility change. The ion association constants obtained in an aqueous solution were related to the extraction constants of the ion associates, and the contributions of the association process and the distribution process were clarified.

Liquid-liquid distribution of ion-associates of acidic dyes with quaternary ammonium counter-ions.

Diprotic acid dyes [H(2)A: Bromophenol Blue (BPB), Bromochlorophenol Blue (BCPB), Bromocresol Purple (BCP), Bromocresol Green (BCG), Bromothymol Blue (BTB)] can be extracted as 1:1 ion-associates Q(+)HA(-) and 1:2 ion-associates (Q(+))(2)A(2-) with quaternary ammonium cations (Q(+)) into chloroform. The extraction constants (log K(ex)) of the 1:1 and 1:2 ion-associates have been determined. Linear relationships between log K(ex) and the number of methylene groups in the quaternary ammonium ions were observed; from the slope of the line, the contribution of a methylene group to log K(ex) was found to be 0.43-0.65. The extractability with alkyltrimethylammonium cations was larger than that with symmetrical tetra-alkylammonium cations, for both the 1:1 and 1:2 ion-associates. From the extraction constants obtained, the extractability of acidic dyes was in the order BTB > BCG > BPB > BCPB > BCP.

Liquid-liquid distribution of ion-associates of dichlorocuprate(I) with quaternary ammonium counter-ions.

The dichlorocuprate(I) anion CuCl(-)(2) can be extracted as its ion-associates Q(+).CuCl(-)(2) with quaternary ammonium cations (Q(+)) into chloroform. The extraction constants K(ex) have been determined, and the log K(ex) values found for the various counter-ions used are 1.93 for (C(3)H(7))(4)N(+), 4.10 for (C(4)H(9))(4)N(+), 6.57 for (C(5)H(11))(4)N(+), 1.57 for C(8)H(17)N(+) (CH(3))(3), 2.83 for C(10)H(21)N(+) (CH(3))(3) 4.12 for C(12)H(25)N(+) (CH(3))(3) and 5.21 for C(14)H(29)N(+)(CH(3))(3), respectively. A linear relationship was found between log K(ex) and the total number of carbon atoms in Q(+); from the slope of the line, the contribution of a methylene group to log K(ex) was calculated to be 0.59. The extractability with alkyltrimethylammonium cations was larger than that with symmetrical tetra-alkylammonium cations and the difference in log K(ex) for two cations (one of each type) with the same number of carbon atoms was about 0.4. From the extraction constants obtained, the extractability of CuCl(-)(2) was found to lie between that of ReO(-)(4) and ClO(-)(4).

Extraction-spectrophotometric determination of boron with 4,6-Di-tert-butyl-3-methoxycatechol and ethyl violet.

4,6-Di-tert-butyl-3-methoxycatechol (DBMC) has been developed as a new reagent for boron, the complex anion formed being extracted as an ion-associate with Ethyl Violet into toluene, and the absorbance measured at 610 nm. The calibration graph is linear up to 0.43 mug of boron, the molar absorptivity is 1.02 x 10(5) 1.mole(-1).cm(-1) and the relative standard deviation 1.2%. The method has been applied to the determination of boron in sea-water and river water with satisfactory results.

Fluorometric determination of nitrite in natural waters with 3-aminonaphthalene-1,5-disulphonic acid by flow-injection analysis.

Nitrite in river and sea-water was determined fluorometrically by flow-injection analysis. In acidic medium, nitrite was reacted with 3-aminonaphthalene-1,5-disulphonic acid (C-acid) to form the diazonium salt, which was converted into the fluorescent azoic acid salt in an alkaline medium. The carrier stream, into which the sample solution was injected, was distilled water. The reagent solution stream, which contained C-acid, EDTA and hydrochloric acid, was mixed with the carrier stream in a 13-m length of Teflon tubing (bore 0.5 mm) maintained at 90 degrees in a thermostatic bath. After passing through the mixing coil, the stream was mixed with an alkaline solution. The fluorescence intensity (excited at 365 nm) was measured at 470 nm. The detection limit (S N = 3) was 1 x 10(-9)M (14 ng 1 . nitrite-nitrogen) and the RSD of 10 injections of 10(-6)M nitrite was 0.4%. Analyses can be done at a rate of up to 45 hr .

Solvent extraction-spectrophotometric determination of phosphate with molybdate and malachite green in river water and sea-water.

Molybdophosphate, formed between orthophosphate and molybdate in sulphuric acid solution, is extracted into a mixture of toluene and 4-methylpentan-2-one (1:3 v v ) with Malachite Green as counter-ion. A single extraction with equal phase volumes gives an apparent molar absorptivity for phosphate of 2.3 x 10(5) l.mole(-1).cm(-1) at 630 nm; the absorbance of the reagent blank is 0.03. With an organic to aqueous phase-volume ratio of 1:10, the molar absorptivity is 2.5 x 10(5) l.mole(-1).cm(-1) and the absorbance of the reagent blank 0.08. By the proposed method, ng ml levels of phosphorus can be determined, and the detection limit is about 0.1 ng ml . The standard deviation and relative standard deviation for the determination of phosphorus in tap water (4.3 ng ml ) are 0.05 ng ml and 1.1%, respectively. The method can also be applied to the determination of phosphorus in river water and sea-water.

Determination of trace amounts of phosphate in river water by flow-injection analysis.

A flow-injection analysis system for the determination of trace amounts of phosphate in river water has been developed. The phosphate is reacted with molybdate and Malachite Green in acidic medium to form a green species, the absorbance of which is measured at 650 nm. Phosphorus (as inorganic phosphate) can be determined at the level of several ng ml in water. Analyses can be done at a rate of up to 40 per hour.

Selection of the counter-cation in the solvent extraction of anionic chelates: Spectrophotometric determination of trace amounts of cobalt with 2-nitroso-1-naphthol-4-sulphonic acid and tetrabutylammonium ion.

The importance of selecting the most suitable counter-cation in the solvent extraction-spectrophotometric determination of an anionic metal chelate containing a sulphonic acid group is demonstrated and discussed. In the case of cobalt and 2-nitroso-1-naphthol-4-sulphonic acid (nitroso-NW acid), the most suitable counter-cation is the tetrabutylammonium ion (Bu(4)N(+)): in this case only the ion-pair of the anionic cobalt chelate is extracted into chloroform and the excess of the nitroso-NW acid remains in the aqueous phase. The absorption maximum of the chelate in chloroform is at 307nm, at which the molar absorptivity is 6.5 x 10(4)l.mole(-1).cm(-1). The absorbance of the reagent blank at 307 nm is less than 0.010. By use of nitroso-NW acid and Bu(4)N(+), trace amounts of cobalt may be determined in nickel salts and in iron and steel samples.