Simultaneous determination of inorganic and organic acids in air by use of annular denuders and ion chromatography

Summary The performance of KOH-coated annular denuders for simultaneous collection of gas-phase atmospheric organic and inorganic acids has been evaluated by ion chromatography (IC) with an NaOH−H₂O gradient. Sampling efficiency was tested for formic and acetic acids under dry and humid air conditions. With this method several mono- and dicarboxylic acids, nitric acid, and hydrogen chloride can be detected. Laboratory and field measurements confirmed the reliability of the denuder method and its superior versatility compared with other techniques (scrubbing by means of a nebulizer, cryogenic trapping) which cannot be used to determine termine gaseous inorganic acids.     

Analysis of alkyl sulfonates and carboxylates using high performance ion chromatography

Summary A simple and general method for the determination of both C₁−C₁₀ alkyl sulfonates and alkyl carboxylates using the same basic methodology, based on High Performance ion Chromatography, using relatively simple eluent systems allowing fast analysis with both high sensitivity and accuracy is presented.     

Electrochemically generated multifunctional suppressor for ion chromatography

Summary A multifunctional suppressor for both anion and cation chromatography has been designed. The suppressor comprises five thin chambers—an anion eluent suppressive chamber, a cation eluent suppressive chamber, a cathode chamber, an anode chamber, and a common electrode chamber, all of which are clipped together. An electrochemical process—electrolysis of deionized water or detector effluent—is used to regenerate the suppressor for continuous operation. Two power sources are used to supply current. The device can work as an anion suppressor, a cation suppressor, or as both anion and cation suppressors, with high suppression capacity (60 mmol L⁻¹) and good reproducibility (RSD=0.80–0.91%) and linearity (r=0.9992).     

Reactions of β-diketiminates with selenium and tellurium halides

The complexes [nacnacTeCl₄] and nacnacSeCl⁺Cl⁻ (nacnac = [{N(C₆H₃ⁱPr₂2,6)C(Me)}₂CH]⁻) have been prepared in good yields and characterized in the solid state by X-ray crystallography. The crystals of both compounds show C-H activation of the ligand backbone. In the case of tellurium, no LiCl displacement or nitrogen chelation is observed and an ionic TeCl₄ complex is isolated. By contrast, under similar reaction conditions, the reaction with SeCl₄, affords a cationic Se(II) complex with loss of four chlorines and rearrangement of the chloride atom to the nacnac ligand.     

Rapid reversed-phase chromatographic separation and determination of selenum and tellurium

Summary The chromatographic behaviour of selenium and tellurium has been investigated with two different reversed-phase chromatographic methods, using P-350 (methyl-bi-isooctyl phosphate) and TBP (tributyl phosphate) as the stationary phases. HCl, HBr, NaCl and NaBr were employed as mobile phase components in both methods. The results suggested that the separation mechanism corresponds to the formation of TeCl (or TeBr) and P-350H (or TBPH) ion associate. A coulometric flow-through detector was applied to determine Se(IV) and Te(IV). Complete separation and quantitative determination of Se and Te could be achieved in 10 minutes.     

Determination of short chain aliphatic acids in silage effluents by ion exclusion chromatography

Summary Short chain aliphatic acids are important components of the dissolved organic matter in silage effluents. Although ion exclusion chromatography offers some advantages for the analysis of these compounds, no attempt has yet been made to prove the suitability of this method for silage effluent analysis. In order to gain experience in this field, the separation characteristics of a Dionex ion exclusion column (IonPac-ICE As5) have been evaluated, the separation conditions have been improved, and several sample clean-up methods have been checked.Ten effluents generated during silaging of five different crops were collected from Bavarian farms and analyzed. Lactic and acetic acids were the predominant aliphatic acids. Pyruvic, formic, propionic, and succinic acid were detected in all samples, whereas glyceric and iso-citric acid were found in a few samples only.If some restrictions of substance specificity and separation efficiency can be accepted, the analytical method presented will be a reliable tool for the analysis of carboxylic acids in silage effluents.     

Potentiometric detection in ion chromatography using a metallic copper indicator electrode

Summary A metallic copper electrode housed in a suitable flowcell is shown to be a sensitive and versatile potentiometric detector for ion chromatography. This electrode may be used for direct or indirect detection of many inorganic anions and cations and also for organic acids. In the direct detection mode, electrode response is based on either complexation of copper ions at the electrode surface by eluted species, or on oxidation and reduction reactions for eluted species which are strong oxidants or reductants. Direct detection is therefore applicable to such species as amino acids, organic acids, chloride, bromide, iodide, chlorate, bromate and iodate. Indirect detection is possible for anions which do not complex copper ions, provided a copper complexing ligand (such as phthalate) is used in the eluent; cations which complex this ligand are also detectable. Indirect detection may be used for species such as nitrite, nitrate, acetate, formate, succinate, benzoate, alkaline earth ions and transition metal ions. Electrode calibration relationships are discussed and sample separations are presented, together with some typical detection limits attainable in the direct and indirect detection modes.Presented in part at a National Symposium on Ion Chromatography, held at the University of New South Wales, Kensington, Australia, Nov. 21, 1984.     

Preparation of silica-based cation-exchangers for use in ion chromatography

Summary A low exchange-capacity, silica-based cation-exchanger for use in ion chromatography has been synthesized. (p-Trimethylsilyl)benzyl-dimethylchlorosilane (TBDCS) reacts with trimethylsilyl chlorosulfonate (TMCS) to produce a compound sulfonated in the para position of the type ArSO₂OSi (CH₃)₃, which is bonded to 5 μm porous silica beads and hydrolysed to the corresponding arylsulfonic acid. The product is hydrophilic and has a high degree of sulfonation, efficiencies of packed columns reaching about 40,000–50,000 plates per meter for the separation of the Mn²⁺ ion. The new stationary phase has been applied to the ion chromatography of some organic and inorganic ions. It is notable that 14 lanthanides can be separated by isocratic elution about one hour on a 150×4·6 mm column, with 4 mM ethylenediamine and 6 mM α-hydroxyl-isobutanoic acid (pH 3.67) as mobile phase. The work was supported by the National Science Foundation of China.     

Simultaneous determination of peroxydisulfate and conventional inorganic anions by ion chromatography with the column‐switching technique

The application of ion chromatography with the column‐switching technique for the simultaneous analysis of peroxydisulfate and conventional inorganic anions in a single run is described. With this method, conventional inorganic anions were separated by consecutive elution through both the guard column and separation column, but peroxydisulfate that only passed through the guard column had a good peak shape and short retention time. A series of standard solutions consisting of target anions of various concentrations from 0.01 to 75 mg/L were analyzed, with a correlation coefficient (r) ≥ 0.9990. The limits of detection were in the range of 0.49–9.84 μg/L based on the S/N of 3 and a 25 μL injection volume. RSDs for retention time, peak area, and peak height were all <1.77%. A spiking study was performed with satisfactory recoveries between 97.6 and 103.4% for all anions. The quantitative determination of peroxydisulfate and conventional inorganic anions in surface waters was accomplished within 18 min by this column‐switching technique.     

Potentiometric detection of monovalent anions separated by ion chromatography using all solid-state contact PVC matrix membrane electrode

Summary An all solid-state contact tubular PVC-matrix membrane electrode has been applied for potentiometric detection of inorganic and organic monovalent anions using phosphate and hydrogen phosphate eluents at low concentrations. This is a “monovalent detection method” as the selectivity of the electrode towards monovalent anions results in some other anions being undetected unless the concentration of those other anions is higher than 10⁻³ mol dm⁻³ in the sample solution injected. It takes only eight minutes to complete the separation with a good resolution. Theoretical and practical considerations are discussed, and in particular, sensitivity, linearity, detection limit and dynamic behaviour are presented. The use of an all solid-state contact bromide-selective electrode as a detector offers so far the best simultaneous sensitivity toward all anions when compared with other detection methods. Determination of Cl⁻ and NO₃ ⁻ ions in river, rain and drinking water samples without any further sample preconcentration has been successfully achieved. The detection limit is sub-ppb for most of anions in a 20 μL injection volume.     

The determination of lactate,acetate, chloride and phosphate in an intravenous solution by non-suppressed ion chromatography

Summary The determination of acetate, lactate, chloride and phosphate in an intravenous solution is investigated using non-suppressed ion chromatography with indirect UV absorption detection. When phthalate eluents are used with low capacity anion-exchange columns, the above solute species cannot be resolved unless acetonitrile is added to the eluent. Optimum results are obtained with 0.3 mM phthalate (pH 6.0) containing 30% acetonitrile as eluent. The improved resolution with this eluent is attributed to the existence of a partial reversed-phase retention mechanism operating on the unfunctionalised portions of the styrene-divinylbenzene polymeric ion-exchange material.     

Hydride generation atomic fluorescence spectrometric determination of ultratraces of selenium and tellurium in cow milk

A sensitive procedure has been developed for selenium and tellurium determination in milk by hydride generation atomic fluorescence spectrometry (HG-AFS) after microwave-assisted sample digestion. The method provides sensitivity values of 1591 and 997 fluorescence units ng⁻¹ ml⁻¹ with detection limits of 0.005 and 0.015 ng ml⁻¹ for Se and Te, respectively. The application of the developed methodology to the analysis of cow milk samples of the Spanish market evidenced the presence of concentration ranges from 11.1 to 26.0 ng ml⁻¹ for Se, and from 1.04 to 9.7 ng ml⁻¹ for Te having found a good comparability with data obtained after dry-ashing of samples.     

Refolding human lysozyme produced as an inclusion body by urea concentration and pH gradient ion exchange chromatography

Summary A new dual-gradient ion exchange chromatographic method was developed to improve the refolding yield of human lysozyme produced inEscherichia coli as an inclusion body. The dissolved and stretched polypeptide chain in a concentrated non-ionic denaturant was adsorbed onto an ion exchange column and induced to refold by gradually decreasing the denaturant concentration and increasing pH in the flowing buffer. The dual gradients of denaturant concentration and pH provided a gradual change of the solution environment along the chromatographic column for the protein to refold, resulting in enhanced activity yield and purity. A post-separation was also studied using size-exclusion chromatography to remove protein aggregates and mis-folded proteins after the refolding step.     

Kinetic spectrophotometric method for simultaneous determination of selenium and tellurium using partial least squares calibration

A kinetic-spectrophotometric method for the simultaneous determination of Se(IV) and Te(IV) is described. The method is based upon the catalytic effect of these cations on the reaction of toluidine blue with sulfide. Partial least squares calibration method was employed for the data manipulation and analysis. The concentrations were varied between 0.02-0.24 and 0.01-0.08 μg/ml for Se(IV) and Te(IV), respectively. Cross-validation method was used to select the optimum number of factors (NF). The root mean square errors of difference for selenium and tellurium were 1.2 and 1.7 μg/ml, respectively. Application of the method to artificial samples and several mixtures of standard solutions of Se(IV) and Te(IV) were performed and satisfactory results were obtained.     

Comprehensive ultra-high pressure capillary liquid chromatography/ion mobility spectrometry

Summary An ultra-high pressure liquid chromatograph was interfaced to a moderately high-resolution nanoelectrospray ionization ion mobility spectrometer operating at ambient temperature and pressure to achieve fast multidimensional separations. The potential of using ion mobility spectrometry as the second dimension in a comprehensive arrangement with liquid chromatography to offer improved qualitative information for compounds under specific operating conditions, is discussed. Separation and detection of selected benzodiazepines and triazine herbicides are demonstrated. Composite peak capacities of 39 and 33 for benzodiazepine and triazine herbicide mixtures, respectively, were achieved in less than 75 s using a 16.5 cm×50 μm internal diameter fused silica capillary liquid chromatographic column packed with 1.5 μm diameter ODS-bonded silica particles.     

Simultaneous analysis of selenate and selenite by single-column ion chromatography

Summary A rapid, selective and sensitive method has been developed for the simultaneous determination of selenate [Se(VI)] and selenite [Se(IV)] at trace levels by single-column ion chromatography. p-Hydroxybenzoic acid (4 mM) at pH 8.0 was used as the eluent. A low capacity resin-based anion-exchange column was employed for the separation with conductometric detection for quantification. The method requires minimal sample pretreatment. Resolution (R_s) between Se(VI)/Se(IV) was 6.76. Chloride, nitrate and sulfate did not interfere with selenium separation. The detection limits for Se(VI) and Se(IV) were 0.06 μg/ml and 0.110 μg/ml, respectively. The relative standard deviation using a 500-μl loop was 0.90 to 1.86% for Se(VI) and Se(IV), respectively. The method was applied to analyze seleniferous soil samples.     

Behaviour of Salbutamol on Diol Normal-Phase Column

Summary The behaviour of salbutamol, a sympathomimetic amine-and catecholamine-like substance, was studied on Diol normal-phase column. The possibility for controlled retention of salbutamol using methanol containing mobile phase was proved. The mobile phase consisted of buffer (0.05 M H₃PO₄, pH 5.0 with TEA) – methanol (15:85 v/v). The effects of organic solvent, pH, ion power of the buffer and the length of amine alkyl chain in buffer were studied. The retention of salbutamol increased significantly with the increase of methanol content above 80%. At pH values between 3.5 and 7.5 the retention of salbutamol varied from 2.16 to 2.36 only. The limit of quantitation was 0.30 ng · mL^–1. The investigations confirm the H-bonding retention mechanism.     

Comparison of provitamin A determination by normal-phase gravity-flow column chromatography and reversed-phase high performance liquid chromatography

Summary The provitamin A content of some food samples was determined by methods involving MgO: Hyflosupercel gravityflow column chromatography (GFCC) and reversed phase high performance liquid chromatography (HPLC), the quantitation being done by external standardization (HPLC-ES) or internal standardization (HPLC-IS) with Sudan. The results obtained with - and -carotene in carrots, -carotene and -cryptoxanthin in papaya and -carotene in tomato and kale agreed well, showing that any of the these techniques can be used, provided the analysis is done under optimum conditions. Good separation of the different provitamins using GFCC depends on the analyst's skill and visual acuity. HPLC-ES required a constant supply of provitamin standards, thus the varying purity of commercially available standards and the high instability of these compounds could pose grave problems. Due to the stability of Sudan, HPLC-IS appeared to be the method of choice although passage of the extract through a MgO: Hyflosupercel minicolumn was required prior to injection to separate chlorophylls, dihydroxy- and polyoxycarotenoids which would otherwise elute with Sudan. Nonconformity of the Sudan structure to those of the provitamins did not effect the quantitative results. The chromatographic separation, identity and quantification of the provitamins could be more easily established by using HPLC-IS, complemented with GFCC.     

A new procedure, based on combustion to sulphate and ion chromatography for the analysis of elemental sulphur in sediments

Summary A procedure exploiting the bomb preparation method for the analysis of total sulphur in organic materials has been developed for the determination of zero-valent sulphur (S^o) in sediments. Sediment samples were dried over magnesium oxide and sonicated in the presence of toluene to extract S^o. Toluene solutions were directly oxidized by combustion in a bomb containing sodium carbonate-bicarbonate buffer, which trapped sulphur species generated from S^o as sulphate ions. These were in turn analysed by suppressed anion chromatography with ion-conductivity detection. The method was used to determine the distribution of S^o in saltmarsh sediment cores.     

Simultaneous determination of preservatives,sweeteners and antioxidants in foods by paired-ion liquid chromatography

Summary A paired-ion, reversed-phase high-performance liquid chromatographic method was developed for the simultaneous determination of sweeteners (dulcin, saccharin-Na and acesulfame-K), preservatives (sodium dehydroacetate, sorbic acid, salicyclic acid, benzoic acid, succinic acid, methyl-para-hydroxybenzoic acid, ethylpara-hydroxybenzoic acid, n-propyl-para-hydroxybenzoic acid, isopropyl-para-hydroxybenzoic acid, n-butyl-para-hydroxybenzoic acid, and isobutyl-para-hydroxybenzoic acid), and antioxidants (3-tertiary-butyl-4-hydroxyanisole and tertiary-butyl-hydroquinone). A mobile phase of acetonitrile-50 mM aqueous -hydroxy-isobutyric acid solution (pH 4.5) (2.2 3.4 or 2.4 3.6, v/v) containing 2.5 mM hexadecyltrimethylammonium bromide and a C₁₈ column with a flow rate at 1.0 mL/min and detection at 233 nm were used. This method was found to be very reproducible with detection limits ranged from 0.15 to 3.00 g. The retention factor (k) of each additive could be affected by concentrations of hexadecyltrimethylammonium bromide and -hydroxyisobutyric acid, and pH and ratio of mobile phase. The presence of additives in some food samples was determined.