Chemiluminescence nitrogen detection in ion chromatography for the determination of nitrogen-containing anions

Chemiluminescence nitrogen detection (CLND) provides equimolar response for nitrogen-containing ions such as nitrate, nitrite, cyanide, ammonium and tetradecyltrimethylammonium. Only azide yields a lower response. Nitrite, azide and nitrate are separated on a Dionex AS11 column using 5 mM NaOH as eluent with a 3 μM (1 ng N) limit of detection. Matrices, such as 1:10 diluted seawater, do not degrade these detection limits. CLND also provides equally sensitive (limit of detection 3 μM, 78 ppb) detection of weak acids such, as cyanide, which yield poor sensitivity with suppressed conductivity detection.     

Ion-interaction chromatography of several metallocyanide complexes stabilized by adding cyanide in a neutral mobile phase.

Standard solutions (at 10(-5) M levels) of Cu(I)- and Fe(II)-cyanide complexes were stabilized for at least 5 h using 0.5 mM cyanide solution (around pH 9) as a medium. Complexes of Cu(I)- and Fe(III)-cyanide also could be stabilized without any dissociation by adding 1 mM cyanide to an acetonitrile-water (18:82, v/v) mobile phase (pH 7.0) containing 10 mM tetra-n-propylammonium salt (TPA). Under the optimal conditions, the six complexes of Cu(I)-, Ag(I)-, Ni(II)-, Fe(II)-, Fe(III)- and Au(I)-cyanides were resolved from their mixtures within about 45 min, with well-shaped chromatographic peaks.     

Electrochemical masking of large amounts of copper in dpasv and the determination of thallium in the presence of a large excess of copper

The influence of the following surfactants on the peak of copper in 0.2M EDTA at pH 4.5 was investigated: polyoxyethylated alkylphenols having an average of 3 and 9.5 ethylene oxide units; polyoxyethylene alcohols having 4 and 7 ethylene oxide units; poly(ethylene glycols) having M.W. 4000, 9000 and 20000; hexadecyltributylphosphonium bromide (HDTBPB), tetraphenylphosphonium bromide (TPPB),N,N,N,N,N',N',N-examethylhexamethylenediammonium bromide (HMB), benzyl(di-isobutylphenoxyethoxy) dimethylammonium chloride (Hyamine 1622), hexadecyltrimethylammonium bromide (HDTMAB), hexadecyldimethylbenzylammonium chloride (HDDMBAC) and tetrabutylammonium chloride (TBAC). HDDMBAC, as well as all the substances examined which contained an ethylene oxide chain, completely suppressed the copper peak. HDTBPB and TPPB partially suppressed the peak, whereas HDTMAB, HMB and Hyamine 1622 enhanced it. TBAC was without effect. In 0.2M EDTA at pH 4.5 containing TBAC at 0.01M concentration and 10 ppm of Rokafenol N-3, Cu(II), Pb(II) and Bi(III) can be tolerated at concentrations of up to 0.05M, the height of the thallium peak being unaffected. The precision of the determination (3–10%) and the recovery are satisfactory. A 10³-fold ratio of Fe(III) to Tl(I) does not interfere with the determination.     

Separation of yttrium and neodymium from samarium and the heavier lanthanides by cation-exchange chromatography with hydroxyethylenediaminetriacetate in monochloroacetate buffer

Trace and mg amounts of yttrium and neodymium are separated from samarium and the heavier lanthanides by elution of the latter with hydroxyethylenediaminetriacetate (HEDTA) in a chloroacetate buffer of pH 2.85 from a column containing 68 ml (20 g) of AG 50W-X4 resin of 200–400 mesh particle size. Yttrium and neodymium (and also praeseodymium, cerium and lanthanum) are retained and can be eluted with 0.01M HEDTA in 0.20M ammonium acetate (pH 6). The separations are reasonably sharp and quantitative: only 3–15 μg of samarium was found in the yttrium fraction and 0.8–3.4 μg of yttrium in the samarium fraction when 4.41 mg of yttrium and 7.12 mg of samarium were present originally. Control of the pH during the column operations is essential because the peak positions are very sensitive to change in pH. The relevant distribution coefficients, elution curves of pairs of elements and results for the analysis of synthetic mixtures are presented. Also included is a method for separating yttrium and the lanthanides from HEDTA and sodium and ammonium ions.     

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.     

Ion-exclusion chromatography of aliphatic car☐ylic acids on a cation-exchange resin by elution with polyvinyl alcohol

Ion-exclusion chromatography of aliphatic car☐ylic acids of different acidity (pK_a) and hydrophobicity was investigated on a polystyrene-divinylbenzene (PS-DVB) based strongly acidic cation-exchange resin in the H⁺ form and conductivity detection by elution with polyvinyl alcohol (PVA). When water was used as an eluent, the resolution of the car☐ylic acids was very low and the peak accompanied a fronting depending on their hydrophobicities. Therefore, to improve the peak shape and the peak resolution, aqueous eluents containing PVAs (degrees of polymerization, n=500, 1500and2000) with many OH groups were tested for the ion-exclusion chromatographic separation of the car☐ylic acids. When aqueous eluents containing PVA were used, the fronting was decreased dramatically by the effect of increased hydrophilicity of the PS-DVB cation-exchange resin surface due to adsorption of OH group in PVA. The high resolution ion-exclusion chromatographic separation without the fronting and highly sensitive conductimetric detection of the car☐ylic acids was accomplished successfully by elution with a 0.2% PVA (n=1500)-10% methanol-water.     

Exchange interaction energy between two one-active electron atoms at large distances

Developed formulas for the exchange interaction energy between two neutral one-active electron atoms interacting at large distances R are presented in terms of known basic integrals obtained from an asymptotic method for the alkali dimers M₂ dissociating to M(ns) + M(ns), M(n′l) + M(n′l), l = 0, …, 3 and M (np) + M(np). Detailed illustrative numerical results are displayed for the molecular states of Na₂ dissociating to the limit Na(3s) + Na(3p). Comparisons with very accurate ab initio results as well as with some available experimental data show that accurate potential energy curves for these excited states may be obtained in a very large range of internuclear distances by connecting ab initio curves for small and intermediate values of R with long-range curves obtained as the sum of usual multipolar Coulombic energy and asymptotic exchange energy.     

Ion chromatographic analysis of cyanate in gold processing samples containing large concentrations of copper(I) and other metallocyanide complexes

An ion chromatographic (IC) method was developed for the determination of cyanate in gold cyanidation samples containing large concentrations of metallo-cyanide complexes. The analysis was performed on a Waters HC IC-Pak A anion-exchange column with an anthranilic acid eluent, with detection achieved using indirect UV at 355 nm. Two procedures were developed for removal of the metallo-cyanide complexes prior to the IC analysis. The first was a manual off-line method which used solid-phase extraction cartridges containing a strong anion-exchange resin to trap the complexes and to then enable determination of cyanate without interference. In the second approach, an automated on-line method was developed which used an anion-exchange guard column to trap the complexes and a column switching valve to allow backflushing of the cyanate from the guard column. This enabled the total analysis to be performed in a time of 10–14 min, depending on the sample composition. Finally, a comparison of results obtained by the standard Kjeldahl nitrogen method for cyanate and the IC method revealed an interference in the Kjeldahl method for samples containing large concentrations of Cu(I)-cyanide complexes.     

螯合离子色谱法分析复杂基体中痕量金属离子的研究

发展了应用螯合离子色谱法分析复杂基体中痕量金属离子的新方法。针对不同的检测目的,利用螯合柱（ＭｅｔＰａｃＣＣ－１）和浓缩柱（ＴＭＣ－１）,采用适当的洗脱液在线将基体中的阴离子、一价阳离子、碱土金属离子以及其它干扰离子除去,同时,浓缩富集待测的痕量金属离子,然后再选择适当的梯度淋洗体系,在含有双功能基的分析柱上分离Ｐｂ,Ｃｕ,Ｃｄ,Ｃｏ,Ｚｎ和Ｎｉ等过渡金属离子和１４种镧系金属离子,继而用在线柱后衍生和光度法检测。方法简单快速,样品经适当的酸消解成溶液后即可进样,灵敏度高,检测限为１０－９级甚至更低。     

Sensitive and selective ion chromatographic method for the determination of trace beryllium in water samples

A selective and sensitive ion chromatographic method has been developed for the determination of beryllium in a number of water samples at low-μg/l concentrations. The separation was performed on a 250×4.0 mm I.D. iminodiacetic acid functionalised silica gel column. Chromatographed Be(II) was detected using visible detection at 590 nm following post-column reaction with chrome azurol S (CAS). The optimum separation and derivatisation conditions were studied in detail. The optimum eluent conditions were found to be 0.4 M KNO₃, adjusted to pH 2.5 using HNO₃, with optimum post-column detection being achieved using a solution containing 0.26 mM CAS, 2% Triton X-100, 50 mM 2-(N-morpholino)ethanesulfonic acid, pH 6.0. Under the above conditions, the concentration detection limit for Be(II) was found to be 3 μg/l in a standard solution and 4 μg/l in a typical tap water sample, using a 250 μl injection. The method was linear over the investigated range of 10 μg/l to 10 mg/l and highly reproducible. The method was successfully applied to a number of water samples of varying matrix complexity, including simulated seawater, and also to a natural freshwater certified reference material NIST 1640.     

Ion chromatography of nitrite and carbonate in inorganic matrices on an octadecyl—poly(vinyl alcohol) gel column using acidic eluents

Low levels of carbonate and nitrite contained in inorganic matrices were determined by ion chromatography on an Asahipak ODP-50 poly(vinyl alcohol) gel-based reversed-phase column. With an acidic mobile phase, inorganic matrix anions and cations eluted near the void volume of the column, whereas carbonate and nitrite were retained and separated completely from the matrix ions. After the separation column, the peak response was enhanced using a cation-exchange hollow fibre and 25 mM sodium sulphate or alkaline enhancers. Sea-water samples can be applied directly for the determination of carbonate and added nitrite at ppm levels. The maximum sample volume that can be loaded on the column without peak deformation depended on the pH of the sample solution and the sulphuric acid concentration in the eluent. A 50 μl sea-water sample was applicable with a 2.5 mM acid eluent.     

Detection of traces of oxidized and reduced sulfur compounds in small samples by combination of different high-performance liquid chromatography methods

Depending on the sulfur species, picomoles of different inorganic sulfur compounds can be detected and separated by HPLC in one arrangement in a sample volume less than 50 μl. The combination of fluorescence labelling of reduced inorganic sulfur compounds such as sulfide (S²⁻), sulfite(SO₃²⁻ and thiosulfate (S₂O₃²⁻) with monobromobimane followed by an extraction of elemental sulfur (S°) by chloroform treatment enables the detection of all mentioned sulfur compounds as well as sulfate (remaining aqueous phase) in the same sample. While the derivatized sulfur compounds could be detected by their fluorescence emission at 480 nm, elemental sulfur is identified by its UV absorption at 263 nm. Sulfate in the remaining aqueous phase is detected by HPLC with indirect UV detection at 254 nm. Detection ranges for the different sulfur compounds examined are as follows: sulfide (5 μM to 1.5 mM), sulfite (5 μM to 1.0 mM), thiosulfate (1 μM to 1.5 mM), elemental sulfur (2 μM to 32 mM) and sulfate (5 μM to >1 mM).     

Determination of metal ions by on-line complexation and ion-pair chromatography

An ion-pair chromatographic method utilizing on-line complexation and ion-pair formation in a post-column reactor was developed for the determination of copper, palladium, cobalt and iron in mixtures. The system features a reversed-phase column and a second eluent line feeding the ligand reagent, connected after the column via a T-piece, to a mixer and through that to a knitted tubing reactor. The ion-pair former was added to the eluent before the column and the ligand after it. The separation was studied using a binary eluent system containing cetyltrimethylammonium bromide (CTMABr) or tetradecyltrimethylammonium bromide (TDTMABr) in water-methanol (99:1, v/v) as ion-pair former and methanol. In addition, water-methanol (99:1, v/v) containing 1-nitroso-2-naphthol-6-sulphonate (126NNS) as ligand was added to the eluent, through the T-piece, after the column. Mixing of the two eluents took place in the mixer. Methanol was used both isocratically and in gradient addition. Selective UV-VIS detection of the metal-126NNS ion pairs was at wavelengths 230, 260, 310 and 400 nm and their identification was effected in wavelength range 190–600 nm. The metal complex formation in the aqueous methanol eluent evidently governed the retention of the ion pairs, while the selectivity of the method was provided by the different rates of reaction of the metal, the ligand and the ion-pair former in the mixer-reactor system. The detector response for copper, palladium, cobalt and iron was linear up to concentrations of 10 μM. In spiked water-methanol samples the detection limits for these metals ranged from 1·10⁻³ to 1 mg/l. When the on-line complexation and ion-pair formation method was tested with nickel, mercury and zinc, the results proved that these ion pairs were unstable. Because of the insufficient reproducibility of the absorption intensities of these metal ion pairs, their qualitative study could be performed only in the pH range 7–8. The method was successfully applied to real samples after removal of the organic material.     

Separation and simultaneous determination of the active ingredients in theophylline tablets by micellar electrokinetic capillary chromatography

The separation and determination of seven active ingredients in theophylline tablets by micellar electrokinetic capillary chromatography is described. On a 35 cm × 50 μm I.D. capillary, baseline separation is possible with a carrier solution containing 0.05 M sodium dodecyl sulphate (SDS) in 0.02 M borate buffer (pH 9.2) solution. The migration time of solutes increased markedly with increasing SDS concentration and slightly with increasing pH. With consecutive injections of samples, slight decreases in the migration times of the solutes occurred, but they were in parallel, owing to the temperature rise of the capillary with time. The column efficiency was influenced by the micellar concentration and applied voltage, and optimum values at which the highest theoretical plate number was achieved were established. The determination of the active ingredients was performed using hydrochlorothiazide and levamisole hydrochyloride (for ephedrine hydrochloride only) as internal standards, with good linearity with correlation coefficients from 0.9965 to 0.9999 and recoveries from 94.1 % to 101.1%. For quantitative information, measurements of peak height were better than peak area.     

Simultaneous determination of arsenic, antimony and tin by fast-scan differential-pulse polarography and its application to alloy steels

Arsenic, antimony and tin can be determined in the presence of one another by fast-scan differential-pulse polarography (FSDPP) on a single mercury drop in 1.5M hydrochloric acid. The reduction of As(III), Sb(III) and Sn(IV) to the metals is practically reversible and the reduction peaks are sufficiently separated. The lower limits of determination are 0.05, 0.005 and 0.001 μg/ml for As, Sb and Sn respectively, the calibration graphs exhibit very good linearity and the peak heights are reproducible. For application to alloy steels employed in nuclear technology, the elements to be determined must be separated from the matrix by extraction as their covalent bromides into toluene from concentrated sulphuric acid and back-extracted into the base electrolyte (1.5M HCl + 0.012M Br⁻ + 0.03M hydrazinium sulphate). The recoveries of As, Sb and Sn are 100, 95 and 92% respectively and the relative error of determination is a few per cent.     

Single-column method of chelation ion chromatography for the analysis of trace metals in complex samples

A single-column chelation ion chromatographic system for the preconcentration and separation of trace transition metals is described. The system includes standard chromatographic equipment with a post-column reagent system based on the reaction with 4-(2-pyridylazo)resorcinol followed by photometric detection at 495 nm. Iminodiacetic acid bonded to 5 μm silica (Diasorb IDA) was used as a chelating stationary phase. The strong complexing ability in combination with good kinetics of complexation and ion-exchange selectivity of iminodiacetic functional groups allow both preconcentration of Mn, Co, Cd, Zn, Ni and Cu from waters of high salinity and efficient separation with the same column. The retention characteristics of alkaline-earth and transition metal ions on Diasorb IDA silica (250×4 mm I.D.) column was investigated for a variety of eluents including nitric acid, maleic, malonic, citric, dipicolinic, picolinic, tartaric and oxalic acids. The influence of ionic strength on retention of metal ions involving high nitrate and chloride concentrations was also evaluated. The baseline separation of preconcentrated metals was achieved using a three-step gradient elution scheme which involved first, flushing of the column loaded with the sample with 0.5 M KCl−0.5mMHNO₃ for 10 min, followed by 80 mM tartaric acid for 20 min and finally 10 mM picolinic acid for 20 min.     

Behaviour of different eluents and stabilizing agents in the determination of sulphite in water by ion-chromatography

Ion-chromatography has been used for the determination of sulphite in water. The eluents were solutions of Na(2)CO(3) (1.1mM)-NaHCO(3) (1.4mM) or NaHCO(3) (1.0mM)-formaldehyde (0.2% w/w), and formaldehyde, glycerol or fructose was used as stabilizing agent. With the first eluent, fructose or glycerol can be used to stabilize samples against sulphite oxidation, but formaldehyde affects the peak height. On the other hand, formaldehyde can stabilize sulphite in the presence of Fe(III), whereas glycerol and fructose can not. If Fe(III) is present, the second eluent is used and sulphite is eluted directly as hydroxymethanesulphonate; formaldehyde will not then affect the peak height. This eluent allows a good peak separation and is suitable for the sulphite concentration range 0.1-12.0 mg/l.     

Applications of enzyme-catalysed reactions in trace analysis-II Determination of cyanide, sulphide, and iodine with invertase

Methods are described for the determination of cyanide (10⁻⁸–10⁻⁵M and sulphide (10⁻⁷–10⁻⁵ M) based on the de-inhibitory effect of these ions on invertase inhibited by mercury(II) or by silver. Iodine (0.1–3 μg) may be determined by its inhibition of invertase.     

Ion chromatography of nitrite at the ppb level with photometric measurement of iodine formed by post-column reaction of nitrite with iodide

The difficulty in ion-chromatographic determination of nitrite in aqueous solutions containing a high concentration of chloride arises mainly from incomplete resolution of the peaks for these anions on the separation column whose efficiency is not high. A photometric measurement of iodine formed by a reaction of nitrite with iodide has been found to make it possible to determine, chromatographically, trace amounts of nitrite without any interference from chloride; chloride does not oxidize iodide to produce iodine. The proposed method was based on the separation of nitrite from matrix anions on a silica-based anion-exchange column with a 1.5·10⁻³ M phthalate eluent (pH 5.0), followed by photometric measurement of the iodine (as triiodide) formed via a post-column reaction of the separated nitrite with iodide. The optimal conditions for the post-column reaction were established by varying the concentrations of iodide, copper(II) and nitric acid in a post-column-reaction solution and the length of a reaction tube. A calibration graph for nitrite, plotted as peak heights versus concentrations, was linear up to 1.50·10⁻⁵ M (690 ppb). The detection limit, defined at S/N=3, was 1.00·10⁻⁷ M (4.60 ppb) nitrite. The presence of chloride ions up to 0.01 M did not give any interference to the determination of nitrite. This method was successfully applied to the determination of nitrite in lake water, river water, sewage works water and snow samples without any pretreatment.     

Accurate determination of traces of sodium and potassium in rocks by ion exchange followed by atomic absorption spectroscopy

Sodium and potassium (5–1000 p.p.m.) in rocks such as peridotites and dunites can be determined accurately by ion-exchange separation followed by atomic absorption spectrophotometry. The samples are decomposed in sulphuric, hydrochloric and hydrofluoric acid mixtures, and after removal of hydrofluoric acid the cations are absorbed on a 90-ml column of AG50W-X8 cation-exchange resin. Vanadium and other anion-forming elements are eluted with 0.01 M nitric acid containing hydrogen peroxide. Then the alkali metals are eluted with 0.50 M nitric acid, while Mg, Mn, Ca, Ti, Al, Fe and other multivalent elements are retained by the column. The eluate fractions containing the respective alkali metals are measured directly by atomic absorption spectrophotometry against standards in 0.50 M nitric acid. Relevant elution curves, results for synthetic mixtures and for three international rock standards are presented and discussed.