Separation of oxyanions of sulphur by single-column ion-chromatography

After stabilization of sulphite by addition of a five-fold excess of formaldehyde, mixtures of sulphite, sulphate and thiosulphate are readily separated by HPLC. For use with Vydac columns (302IC or 300IC) a suitable eluent is 1-3mM phthalic acid (pH 5-6), and the eluted ions may be detected by means of the change in refractive index or the absorbance at 290 nm. With a flow-rate of 2 ml/min, anion elution times are about 2.7 (0.7) min for HOCH(2)SO(-)(3), 7.5 (2.6) min for SO(2-)(4) and 8.4 (5.2) min for S(2)O(2-)(3), the values in parentheses being those for the shorter 300IC column. Detection limits for sulphite and sulphate were around 1 mg/l., with relative standard deviations of 2-3% at higher levels. The sensitivity for S(2)O(2-)(3) was an order of magnitude lower. The proposed method has advantages over earlier procedures based on alkaline eluents.     

The ion chromatographic separation of high valence metal cations using a neutral polystyrene resin dynamically modified with dipicolinic acid

A neutral polystyrene resin column, dynamically loaded with dipicolinic acid at a concentration of 0.1 mM in 1 M potassium nitrate eluent, was investigated for the separation characteristics of a number of high valence metal cations over the pH range 0-3. The metal species studied were Th(IV), U(VI), Zr(IV), Hf(IV), Ti(IV), Sn(IV), V(IV) and V(V), Fe(III) and Bi(III), of which Ti(IV), Sn(IV), V(IV) and Fe(III) did not show any retention. For the remaining metal ions, significant retention was obtained with good peak shapes, except for Th(IV), which moved only slightly from the solvent front with some tailing. The retention order at pH 0.3 was Th(IV) < V(V) < Bi(III) < U(VI) < Hf(IV) < Zr(IV). A notable feature of this separation system was the high selectivity shown for uranium, zirconium and hafnium, the last two being nearly resolved in 15 min on the relatively short 10 cm column.     

Determination of [S,S']-ethylenediaminedisuccinic acid by high-performance liquid chromatography

A new high-performance liquid chromatography (HPLC) method for the determination of ethylenediaminedisuccinic acid (EDDS) is presented. Free EDDS(4-) and EDDS complexes with divalent metals undergo conversion to the Fe(III) complex in the presence of Fe(III)Cl(3). Fe(III)EDDS is separated by HPLC on an ion exchange column using (NH(4))(2)SO(4) eluent with detection at 258 nm. The detection limit is 0.01 microM. The method is applied to natural waters and soil solution samples. A background of natural water results in a reduction in EDDS peak area. The method is suited for EDDS analysis in samples with well-defined, simple matrices such as those used in laboratory experiments or biodegradation studies.     

Steady-state and flow-injection response of a metallic silver electrode for potentiometric detection of metal cyanide complex formartion

A metallic silver electrode provides a potentiometric response to Ag(I), Hg(II), Fe(III), Cu(II), Zn(II), Co(II) and Ni(II) ions, and large changes in the electrode potential of up to 400 mV are observed when these ions are injected into a 0.29 mM soulution of cyanide ion. Injection 10-μl aliquots into a reagent stream with a cyanide concentration of 0.1 mM is shown to give the expected sigmoidal-shaped response curve for peak height as a function of metal ion concentration. Sub-nanomole quantities of metal ions are detectable with a peak height of ca. 20 mV, depending on the cyanide concentration.     

High-performance liquid chromatography of micelle-solubilized complexes-IV Reversed-phase ion-pair chromatography of metal-3,5-diBr-PADAP-Triton X-100 complexes

The micellar solubilization complex systems of V(V), Cu(II), Zr(IV), Pd(II), Fe(III), Ni(II) and Co(II) with 3,5-diBr-PADAP and Triton X-100 have been investigated by HPLC on an ODS (5 x 250 mm) column with a ternary eluent of methanol-acetone-acetone-water containing TBA(+) and acetate buffer (pH 3.0) at 600 or 572 nm wavelength for the detection of the complexes. An HPLC-spectrophotometric method for determination of seven metal ions has been developed. The peak height calibration curves are linear up to 50-100 mu/1, metal ion concentration. The relative standard deviations for the determination of 30.0 mu/1 metal ion were 0.9-1.6% and the detection limits (S/N = 3) were 1.1-3.6 mug/1.     

Voltammetric response of phenylboronic acid monolayer-modified gold electrode to sugars.

The surface of a gold (Au) disk electrode was modified with a self-assembled monolayer consisting of phenylboronic acid moiety to fabricate a voltammetric sensor sensitive to sugars. The modified Au electrode exhibited a voltammetric response to sugars in the presence of Fe(CN)6(3-) ion in the sample solution at neutral pH. The peak current of the cyclic voltammograms decreased depending on the type and concentration of sugars. The dynamic range of the electrode is 3 - 100 mM for glucose and mannose and 1 - 30 mM for fructose. The sugar sensor can be used repeatedly after rinsing in 10 mM acetate buffer (pH 4.5).     

Use of a copper electrode in alkaline medium as an amperometric sensor for sulphite in a flow-through configuration

A flow injection analysis (FIA) method has been developed for the determination of sulphite in beverages. The method is based on the amperometric detection (0.60 V vs Ag/AgCl (sat. NaCl)) of the analyte at a copper surface in an alkaline medium (1 M NaOH solution) with a manifold that incorporates flow extraction of sulphite as SO2 through a PTFE membrane. Under optimal experimental conditions the peak current response increases linearly with sulphite concentration over the range from 1.0 to 5.0 mM. The repeatability of the electrode response in the FIA configuration was evaluated as 4% ( n =20), the limit of detection of the method was 0.04 mM (S/N =3) and the analytical frequency was 50 h(-1). Since ethanol is also electroactive and permeates through the PTFE membrane, a strategy involving in a first step measurements of only ethanol by manipulating the pH of the donor stream was employed for wine samples. Then, both ethanol and sulphite were measured at the copper electrode at 0.40 V vs Ag/AgCl (sat. NaCl) and the sulphite concentration was determined by difference. Results for 3 different beverage samples (alcoholic and non-alcoholic) showed excellent agreement with the ones obtained by using a recommended procedure for sulphite analysis.     

Determination of synthetic ferric chelates used as fertilizers by liquid chromatography-electrospray/mass spectrometry in agricultural matrices

A high-performance liquid chromatography-electrospray ionization/mass spectrometry (time of flight) method has been developed for the simultaneous determination of synthetic Fe(III)-chelates used as fertilizers. Analytes included the seven major Fe(III)-chelates used in agriculture, Fe(III)-EDTA, Fe(III)-DTPA, Fe(III)-HEDTA, Fe(III)-CDTA, Fe(III)-o,oEDDHA, Fe(III)-o,pEDDHA, and Fe(III)-EDDHMA, and the method was validated using isotope labeled (57)Fe(III)-chelates as internal standards. Calibration curves had R values in the range 0.9962-0.9997. Limits of detection and quantification were in the ranges 3-164 and 14-945 pmol, respectively. Analyte concentrations could be determined between the limits of quantification and 25 muM (racemic and meso Fe(III)-o,oEDDHA and Fe(III)-EDDHMA) or 50 muM (Fe(III)-EDTA, Fe(III)-HEDTA, Fe(III)-DTPA, Fe(III)-CDTA and Fe(III)-o,pEDDHA). The average intraday repeatability values were approximately 0.5 and 5% for retention time and peak area, respectively, whereas the interday repeatability values were approximately 0.7 and 8% for retention time and peak area, respectively. The method was validated using four different agricultural matrices, including nutrient solution, irrigation water, soil solution, and plant xylem exudates, spiked with Fe(III)-chelate standards and their stable isotope-labeled corresponding chelates. Analyte recoveries found were in the ranges 92-101% (nutrient solution), 89-102% (irrigation water), 82-100% (soil solution), and 70-111% (plant xylem exudates). Recoveries depended on the analyte, with Fe(III)-EDTA and Fe(III)-DTPA showing the lowest recoveries (average values of 87 and 88%, respectively, for all agricultural matrices used), whereas for other analytes recoveries were between 91 and 101%. The method was also used to determine the real concentrations of Fe(III)-chelates in commercial fertilizers. Furthermore, the method is also capable of resolving two more synthetic Fe(III)-chelates, Fe(III)-EDDHSA and Fe(III)-EDDCHA, whose exact quantification is not currently possible because of lack of commercial standards.     

A novel ion chromatographic method based on cation-exchange and acid-base interactions for the simultaneous determination of total alkalinity and monovalent cations in samples of microliter volume

An ion chromatographic (IC) method based on the use of titrant (strong acid) as the stationary phase was developed for simultaneous determination of total alkalinity (TA) and monovalent cations. The titrant used in this study was obtained by initially loading lithium dodecylsulfate (Li-DS) onto a reversed-phase material and then conditioning the column with a slightly acidified aqueous LiCl solution (a mixture of 50.0 mM LiCl and 0.1 mM H2SO4). When a small amount of a basic sample was injected onto a column prepared in this way, the basic species (Bn-) reacted predominantly with H+ on the stationary phase and the reaction with the eluent phase was negligible due to the very low concentration of eluent H+ (in the eluent, a molar ratio of [Li+]/[H+] = 250:1 applied). The stationary phase H+ consumed in the acid-base reaction was then re-supplied by H+ from the eluent. By monitoring the conductance of the eluent using conductivity, an induced peak resulting from the basic species was observed. Calibration graphs of peak areas vs. molar concentration of the basic species for OH-, HCO3- and H2PO4- were found to be identical. CO3(2-), HPO4(2-), and B4O7(2-) also gave identical calibration curves but their slope values were twice those for HCO3-. The detection limit for HCO3- was less than 3.2 microM and the calibration curve was linear up to 12.3 mM (injection volume, 100 microL). Seawater was directly analyzed and its total alkalinity was found to be 2.87 mM (RSD 0.53%, n = 5), which was in good agreement with the result of 2.88 mM (RSD 3.2%, n = 5) obtained using auto-potentiometric titration. Na+ and K+ were determined simultaneously and the concentrations were 481.6 and 10.6 mM, respectively.     

Cathodic stripping determination of iron at a platinum electrode modified by adsorption of adenosine-5'-monophosphate

Irreversible adsorption of adenosine-5'-monophosphate onto platinum yields an electrode surface which is readily plated by formation of a non-labile complex with iron(III) present initially in solution or formed by oxidation of iron(II). A negative potential scan subsequent to a 60-s deposition step produces a cathodic stripping peak, the height of which is proportional to the sum of the Pe(III) and Fe(II) concentrations in solution. Oxalate can be used to mask the response to Fe(III). The method is shown to be applicable to determinations of Fe(III) and Fe(II) in the concentration range lO^-8–lO^-6 mol l^-1.     

Separation and determination of carbohydrates in drinks by ion chromatography with a self-regenerating suppressor and an evaporative light-scattering detector

Analysis of glucose and other carbohydrates are often performed by use of normal phase HPLC methods with acetonitrile as major eluent coupled with evaporative light-scattering detector (ELSD) or by use of anion-exchange ion chromatography (IC) methods with NaOH as eluent coupled with pulsed amperimetric electrochemical detector. In this work, a novel method for the determination of carbohydrates by IC in conjunction with a self-regenerating suppressor and an ELSD detector was investigated. Three carbohydrates (glucose, fructose, and sucrose) were separated using a KOH eluent generator to avoid the effect of carbon dioxide absorption in the alkaline eluent. Due to the use of the suppressor, non-volatile components were removed and a low salt background (K+ approximately 0.070 microg/mL) can be obtained so the suppressed eluent could directly go into an ELSD detector without obvious interference of inorganic salts. After examining the changes in retention and resolution, an optimized method was established (for IC: using 32 mM KOH as the eluent at a flow rate of 1 mL/min; for ELSD: operated at 95 degrees C, 4.0 bar nitrogen with a gas flow rate of 2.0 L/min) and the linearity, reproducibility, and the limit of detection (LOD) for the three carbohydrates were further evaluated. Regression equations revealed acceptable linearity (correlation coefficients=0.994-0.998) across the working-standard range (100-1000 microg/mL for glucose and sucrose, 150-1000 microg/mL for fructose) and LODs of glucose, fructose, and sucrose were 93, 126, and 90 microg/mL, respectively. This method has successfully been applied to the determination of the three carbohydrates in carbonated cola drinks and fruit juices. The recoveries were between 95 and 113% (n=3) for different carbohydrates.     

Molecular emission cavity analysis : Part XI. The determination of carbonyl compounds

Formaldehyde (2–750 μg), acetaldehyde (0.05–1.0 μg) and acetone (0.4–3.5 smg) can be determined in aqueous solution (? 17.5 ml) by MECA. Sodium sulphite solution (5 ml, 500 p.p.m. S) and 1.5 ml of l M phosphoric acid are added and the delayed S₂ emission from the sulphite addition compound in 5 ml of the solution is measured in a MECA cavity; a hydrogen-nitrogen flame is used. Mixtures of formaldehyde and acetone can be determined simultaneously on the basis of the resolved MECA peaks of their sulphite addition compounds, after evaporation of the excess of sulphite from the cavity.     

Ion-exclusion/cation-exchange chromatographic determination of common inorganic ions in human saliva by using an eluent containing zwitterionic surfactant

Ion-exclusion/cation-exchange chromatography with an eluent containing the bile salt-type zwitterionic surfactant CHAPS was performed in order to evaluate variations in anion (SO(4)(2-), NO(3)(-), and SCN(-)) and cation (Na(+), K(+), NH(4)(+), Mg(2+), and Ca(2+)) concentrations in human saliva. CHAPS prevents the adsorption of proteins to the stationary phase, i.e., weakly acidic cation-exchange resin, since it aggregates proteins without denaturing them. Addition of 1mM CHAPS to the eluent comprising 6mM tartaric acid and 7 mM 18-crown-6 yielded reproducible separations of anions and cations in protein-containing saliva. The resolutions of anions and cations were not significantly affected by the addition of CHAPS to the eluent. The concentrations of Na(+) and K(+) varied before and after meals; or that of SCN(-), upon smoking. The relative standard deviations of peak areas ranged from 0.3 to 5.1% in 1 day (n=20) and from 1.4 to 5.8% over 6 days (n=6).     

Micellar chromatographic separation of vanadium(V) chelate with 2-(2-thiazolylazo)-5-dimethylaminophenol

Summary In reversed phase—high performance liquid chromatography for metal chelates with 2-(2-thiazolylazo)-5-dimethylaminophenol, an aqueous non-ionic surfactant solution is used as a mobile phase. Among V(V), Fe(III), Cu(II), Co(II), Ni(II), Cd(II), Zn(II), Mn(II), and Al(III), only the V(V) chelate gave a resolved peak by using 0.8% w/w poly(oxyethylene)_n-4-nonylphenyl ether (n=20) solution buffered at pH 3.8. V(V) can be selectively separated and sensitively determined.     

Determination of iodide in seawater using C30 column modified with polyoxyethylene oleyl ether in ion chromatography

An ion chromatographic method for rapid and direct determination of iodide in seawater samples is reported. Separation was achieved using a laboratory-made C30 packed column (100 mm × 0.32 mm i.d.) modified with polyoxyethylene oleyl ether, with an aqueous solution of 300 mM sodium chloride as eluent and using UV detection at 220 nm. Samples containing iodate, nitrate, iodide and thiocyanate were eluted within 8 min, and the relative standard deviations of the retention time, peak area and peak height were all smaller than 4.19% for all of the analyte anions. Effects of eluent composition on retention behavior of inorganic anions have been investigated. Both cation and anion of the eluent affected the retention time of analytes. When inorganic eluents, such as ammonium chloride, ammonium sulfate, lithium chloride, sodium chloride, sodium sulfate, magnesium chloride and magnesium sulfate were used, the retention time of analytes increased with increasing eluent concentration. The limit of detection of iodide was 19 μg l⁻¹ (S/N = 3), while the limit of quantitation was 66 μg l⁻¹ (S/N = 10). The present method was successfully applied to the rapid and direct determination of iodide in seawater samples.     

非离子表面活性剂胶束增溶显色反应机理的研究 III:在Fe(III)-PAN-Triton X-100体系中胶束对金属离子反应活性的影响

Fe (III) and PAN form the complex Fe(PAN)2OH which can be extracted into CHCl3. The CHCl3 extract shows absorption maxima at 550 nm and 775 nm (log E550 = 4.06, log e775 = 4.08). In the Fe(III)--PAN--Triton X-100 system, two complex species (Fe(PAN)2)+ and/or Fe(PAN)2OH may be formed. (Fe(PAN)2)+ exhibits a stronger absorption peak at 550 nm (log E550 =4.36). In this paper the effect of Triton X-100 micelles on the Fe(III)-PAN reaction has been investigated in detail. We consider that the presence of high density of ethereal oxygen chains in Triton X-100 micelles enables to concentrate hydrated Fe(III) ions and change their existing state. Moreover, the micelles not only increase the reactivity of Fe(III), but also enhance the rate of the color reaction.     

Studies on the separation of hydronium ion using surfactant-modified reversed-phase stationary phases and eluents containing an acidified electrolyte

A further investigation of a chromatographic system allowing determination of hydrogen ions is reported. For this purpose an octadecylsilica column dynamically modified with sodium dodecylsulfate (SDS) or lithium dodecylsulfate (LDS) was used as stationary phase and a slightly acidified electrolyte (usually KCl)-SDS solution was used as the eluent. The concentration of SDS, KCl and the acidity of the eluent affected the structure of aggregates formed by the molecules of dodecylsulfate at the surface of the stationary phase. These aggregates of dodecylsulfate were found to be responsible for the appearance of a chromatographic peak attributed to the presence of H3O+ ions in a sample. Other cations in the sample could be separated in the same manner, permitting the simultaneous separation of monovalent cations from H3O+. The detection limit for H3O+ ions was 2.25 x 10(-6) M using an eluent comprising 0.3 mM LDS, 50.0 mM KCl and 0.10 mM H2SO4. The proposed method is shown to be applicable for the determination of free H3O+ ions in aqueous solutions of strong acids.     

Determination of glycerol, 1,2-propanediol and triglycerides by high-performance liquid chromatography and a post-column reactor containing immobilized glycerol dehydrogenase

A fluorimetri method is described for the determination of glycerol, 1,2-propanediol and triglycerides in serum by high-performance liquid chromatography with an on-line post-column reactor containing immobilized glycerol dehydrogenase. Before separation, triglycerides are cleaved with lipase and esterase. The polyhydric alcohols are separated from each other on a Finepak SIL C₁₈ (10 μm) column with water as eluent. The NADHI produced from the enzymatic reaction is monitored by fluorimetry. Calibration curves are linear between 0.01 mM and 1.0 mM for glycerol or 2.0 mM for 1,2-propanediol. The method gave satisfactory results for control sera.     

Effective on-line coupling of HPLC and flame-AAS by means of hydraulic high pressure nebulization

Summary Hydraulic high pressure nebulization is used as an effective way of on-line coupling of HPLC to flame-AAS for speciation of metal compounds in the ng range. Compared to coupling with a conventional nebulizer a signal enhancement by a factor of 7.5 (peak height) and 10.1 (peak area) for copper is obtained. Using an injected volume of 50 μL the detection limits for Cu, Fe, Ni and Cd are below 0.1 μg/mL (=5ng) and for Mg below 0.01 μg/mL (=0.5ng). The effects of HPLC flow-rate and nebulization nozzle diameter on the signal peak height have been investigated. The performance of the system is demonstrated using speciation of iron. A base-line separation of Fe(II) and Fe(III) is achieved within two minutes. Also species changes (Fe acetate to Fe citrate) can be analysed using the proposed system.     

The protonated 4,4'-diaminotriphenylmethyl cation as a reagent and cyclohexanone as an absorbant for sulphur dioxide determination

Protonated 4,4'-diaminotriphenylmethyl cation, DATM, has been investigated as a colorimetric reagent for the determination of sulphur dioxide. The bisulphite addition compound with formaldehyde alkylates a primary arylamine group in the protonated reagent to re-establish resonance, and hence produces a colour that is proportional in intensity to the concentration of either bisulphite or formaldehyde (the other being in excess). The large bathochromic spectral shift results in a negligible blank correction. Cyclohexanone in aqueous solution has been found to stabilize bisulphite solutions for up to 6 hr. The stabilization by cyclohexanone has been compared with stabilization by tetrachloromercurate(II). The Beer-Lambert law is obeyed with good precision for both sulphite and formaldehyde determination.