Showing papers in "Analyst in 1986"

Directly coupled chromatography-atomic spectroscopy. Part 1. Directly coupled gas chromatography-atomic spectroscopy. A review

Abstract: Revue detaillee de 100 references classees par methodes couplees (chromatographie en phase liquide couplee a spectrometrie d'absorption atomique de flamme, a atomisation electrothermique, spectrometrie de fluorescence atomique de flamme, spectrometrie d'emission optique) presentee sous forme de tableaux avec des details sur le detecteur, la methode, l'echantillon, des commentaires, l'element analysee

Selective reduction of arsenic species by continuous hydride generation. Part I. Reaction media

Abstract: Continuous hydride generation, using sodium tetrahydroborate(III) as a reductant in conjunction with atomic absorption spectrometry (AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES), has been used to form arsines selectively from arsenate (AsV), arsenite (AsIII), monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA). The reaction media studied have been shown to allow the rapid determination of AsIII alone, DMAA alone, AsIII+ AsV and “total” arsenic, i.e., AsIII+ AsV+ MMAA + DMAA. Interference effects produced by heavy metal ions are suppressed by the addition of masking agents.

Mercury(II) and silver(I) ion-selective electrodes based on dithia crown ethers

Abstract: Mercury (Hg2+) and silver (Ag+) ion-selective PVC membrane electrodes based on 1,4-dithia-12-crown-4 and 1,4-dithia-15-crown-5 as neutral carriers were successfully developed. Both electrodes exhibited good linear responses of 30 and 40 mV decade–1 for Hg2+ and Ag+, respectively, within the concentration ranges 10–2-10–6M Hg(NO3)2 and 10–1-10–6M AgNO3. Some other crown ethers and cryptands were also investigated as neutral carriers for both ions. Both the mercury and silver electrodes exhibited comparatively good selectivities for mercury(II) and silver(I) ions in comparison with alkali metal, alkaline earth metal and some heavy metal ions. These crown ether ion-selective electrodes are suitable for use with aqueous solutions at pH 2. They were applied as sensors in titrations of Br– and Cl– with Ag+ and of Hg2+ with l– and Cr2O72– and in the determination of the solubility products of AgCl in aqueous solutions.

Determination of morphine by flow injection analysis with chemiluminescence detection

Abstract: Chemiluminescence detection has been used in combination with flow injection analysis to determine 1 fmol of morphine by its reaction with permanganate in an acidic tetraphosphate solution. Structurally similar narcotics can also be determined by the same procedure. A mechanism for the chemiluminescent reaction is suggested.

Experimental Artifacts and Determination of Accurate Py Values

Abstract: Recently the Py solvent scale has been introduced and a large body of data has been generated using fluorescence measurements. Numerous problems exist in the correct determination of these values, including instrumental and chemical artifacts. Among the instrumental problems associated with correct Py assignments are slit width effects, inner filtering and efficiencies associated with double-pass vs. single-pass cell compartment designs. These instrumental problems, together with chemical artifacts related to adequate blank correction and temperature control, were investigated in the work reported in this paper.

Determination of inorganic and organomercury compounds by high-performance liquid chromatography-inductively coupled plasma emission spectrometry with cold vapour generation

Abstract: An inductively coupled plasma (ICP) emission spectrometer was used as a high-performance liquid chromatographic detector for the determination of mercury compounds. Post-column cold vapour generation was used to obtain improved detection limits. The replacement of the conventional polypropylene spray chamber of the ICP by an all glass chamber is described. A comparison of band broadening indicates that the glass chamber is useful when a severe memory effect is observed with the polypropylene spray chamber. Detection limits ranged from 32 to 62 p.p.b. of mercury for four mercury compounds, based on a signal to noise ratio of 2:1. This represents a three to four order of magnitude enhancement over detection limits obtained without cold vapour generation. The approach is linear over three orders of magnitude. A blind, spiked distilled water study illustrates the reproducibility and accuracy of the method.

Improved routine method for the determination of total iodine in urine and milk

Abstract: A simple routine method for the determination of iodine in biological fluids is proposed. Destruction of organic matter by alkaline ashing is carried out prior to determination by the Sandell and Kolthoff reaction. The precision is below 8% for urine and milk. Iodine contents as low as 2 ng g–1(p.p.b.) can be detected.

Ion-selective electrode for the determination of metoclopramide

Abstract: A metoclopramide (MCP) ion-selective PVC membrane electrode based on the ion-pair complex of MCP with sodium tetraphenylborate was prepared with dioctyl phthalate as a plasticiser. The electrode exhibits a linear response with an approximate Nernstian slope (50 mV decade–1 at 20 °C) within the concentration range 10–1.7–10–5.6M MCP. The effects of ionic strength and pH of the test solution on the electrode performance were studied. The electrode exhibited very good selectivity for MCP with respect to a large number of inorganic and organic cations of biological importance. The standard additions method and potentiometric titration were used to determine the MCP in pure solutions and in pharmaceutical preparations with satisfactory results.

Procedure for the construction of all-solid-state PVC membrane electrodes

Abstract: A procedure for the construction of all-solid-state PVC membrane electrodes, which consists in depositing the PVC membrane on a conductive epoxy support mounted in a Perspex body, has been developed. The technique was tested for potassium-, nitrate- and calcium-selective electrodes with Corning 477317, Orion 92-07-02 and Orion 92-20-02 commercial sensors, respectively, whose response characteristics are presented. The advantages and shortcomings of the new type of selective device are discussed.

Determination of lead in blood by atomic absorption spectrometry with electrothermal atomisation

Abstract: A method is described for the routine determination of lead in whole blood by electrothermal atomisation from a L'vov platform and atomic absorption spectrometry. The sample preparation is a simple 1 + 19 dilution with a diluent containing a mixture of NH3 solution, NH4H2PO4 and (NH4)2H2EDTA. Further chemical modification is achieved using in situ oxygen ashing during electrothermal sample decomposition at 550 °C. Desorption of oxygen at 950 °C without losses of lead gives tube lifetimes of 200–250 firings. The calibration graph, established with matrix-matched standards and using integrated absorbance measurements, is linear for concentrations up to 5 µmol l–1. The detection limit is 8.3 × 10–12 g or 0.08 µmol l–1 of lead in blood. The within- and between-run precisions are 6.9% and 7.3%, respectively, at 0.5 µmol l–1 of lead, and the accuracy of the method is demonstrated by the excellent agreement with the results of micro-sampling flame atomic absorption spectrometry and with group mean values in external quality assessment programmes.

Determination of dissolved aluminium by the micelle-enhanced fluorescence of its lumogallion complex

Abstract: A sensitive modification of the lumogallion fluorescence assay for aluminium is presented that exploits the 5–6-fold increase in the fluorescence intensity of the lumogallion-aluminium complex in the presence of the non-ionic detergent Triton X-100. The sensitised procedure has a detection limit of 0.02 µg l–1 of Al (3σ) and a relative standard deviation of 5% at the 0.1 µg l–1 of Al level. The sensitivity of the method is independent of salinity and it can be used for the determination of aluminium in both fresh and saline waters. The interference from iron experienced in the conventional lumogallion procedure is also present in the modified method, but can be masked by the addition of 1,10-phenanthroline.

Automated flow injection spectrophotometric determination of some phenothiazines using iron perchlorate: applications in drug assays, content uniformity and dissolution studies

Abstract: An automated flow injection determination of some phenothiazine derivatives, based on their oxidation with iron(III) in a strongly acidic medium, is described. Chlorpromazine, promethazine, thioproperazine, promazine, levomepromazine, fluphenazine, trifluoperazine and thioridazine are determined in the range 10–250 µg ml–1. The precision is better than 1% and a measurement rate of 120 per hour can be obtained. The method was evaluated by carrying out an interference study with common excipients and other drugs, a recovery study and by the analysis of commercial formulations, the results of which are compared with those obtained by the official method. The method was applied in content uniformity tests and for monitoring the dissolution of solid dosage forms.

Determination of 28 elements in american cigarette tobacco by neutron-activation analysis

Abstract: The concentrations of 28 toxic and other elements in cigarette tobacco of twelve brands commercially manufactured in the USA were determined using instrumental neutron-activation analysis. The elements determined were Al, As, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Eu, Fe, Hf, K, La, Mg, Mn, Na, Ni, Rb, Sb, Sc, Se, Sr, Th, Ti, V and Zn. The concentrations of the determined elements in the American cigarettes were compared with the elemental concentrations reported for Iranian, Pakistani and Japanese brands. It was concluded that the concentrations of As, Br, Ca, Eu, K and Zn in the samples under investigation are lower than those reported for the analysis of University of Kentucky reference cigarettes, whereas the concentrations of Mn and Na are higher. The contents of Al, Cl, Co, Cr, Cs, Fe, La, Sb, Sc and Se are similar to those in the reference cigarettes.

Selective reduction of arsenic species by continuous hydride generation. Part II. Validation of methods for application to natural waters

Abstract: Preliminary research has been concerned with the selective determination of arsenate (AsV), arsenite (AsIII), monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) using continuous hydride generation and atomic absorption spectrometric detection. These studies (Part I) highlighted certain media as being suitable for monitoring AsIII, AsIII+ AsV, DMAA alone and AsIII+ AsV+ MMAA + DMAA. Details are provided of the application of these procedures to the determination of arsenic species in contaminated streams draining mineralised areas of Cornwall. The data generated have been compared with those produced by a cold-trapping technique and statistical methods have been utilised to test the analytical accuracy.

Use of cerium(IV) sulphate in the spectrophotometric determination of paracetamol in pharmaceutical preparations

Abstract: An accurate spectrophotometric method is proposed for the determination of paracetamol. Cerium(IV) sulphate is used to oxidise paracetamol in 5 M H2SO4 to p-benzoquinone, which is then determined at 410 nm. The method has been successfully applied to the analysis of commercial pharmaceutical preparations and the results have been statistically compared with those obtained by the official (BP) method.

Titrimetric determination of catecholamines and related compounds via bromine oxidation and substitution.

Abstract: A titrimetric method for the determination of 0.1–10 mg of catecholamines and related compounds as pure substances and in their dosage forms was investigated and found to offer improvements with regard to ease, speed and accuracy. The method is based on bromine oxidation of the catecholamines (adrenaline, noradrenaline, L-dopa, dopamine and methyldopa) to the corresponding benzoquinones; related compounds (octopamine, tyramine and tyrosine) undergo substitution to the dibromoaryl hypobromites. The benzoquinones and hypobromites oxidise iodide to liberate stoicheiometric amounts of iodine, which can be determined titrimetrically with thiosulphate, using starch as an indicator.

Amperometric enzyme electrode system for the flow injection analysis of glucose.

Abstract: A flow injection system incorporating an amperometric enzyme electrode is described. Glucose oxidase immobilised on nylon mesh and held over a platinum electrode formed the basis of the electrode, which was incorporated in a three-electrode amperometric Stelte cell, modified for flow injection analysis. The flow and enzymatic reaction conditions have been optimised for maximum glucose response. The system exhibited good linearity (0.01 to 3.0 mM glucose), short response times (<45 s), good capacity (24 h with a continuous flow of 2.5 mM glucose) and long lifetimes (up to 4 months with storage at 4 °C). Data for the determination of glucose in foodstuffs with the enzyme electrode were similar to those obtained by the Yellow Springs Instrument glucose analyser and a soluble enzyme test kit (Boehringer Mannheim method).

Differential-pulse adsorptive stripping voltammetry of food and cosmetic synthetic colouring matters and their determination and partial identification in tablet coatings and cosmetics.

Abstract: Sixteen food and two cosmetic synthetic colouring matters were shown to adsorb strongly on a hanging mercury drop electrode and to be amenable to determination by differential-pulse adsorptive stripping voltammetry. When a 2-min accumulation time was used, the increase in sensitivity over differential-pulse polarography at a dropping mercury electrode was between 8- and 100-fold, depending on the colouring matter determined. Using longer accumulation times, 1 × 10–10M concentrations of some food colours could be determined. The addition of tetraphenylphosphonium chloride shifted the reduction potentials of some colouring matters to more negative values and either decreased or increased the size of the peaks obtained. This makes it a useful reagent for partially identifying individual colouring matters even when they are present at very low concentrations. Increased sensitivity was obtained with carmoisine, tartrazine and quinoline yellow by its addition.Procedures for applying the method to the determination and partial identification of colouring matters in tablet coatings and in a lipstick have been developed. The need to dilute more concentrated sample solutions has the advantage of eliminating matrix effects, which are sometimes apparent when differential-pulse polarography is applied without dilution.

Novel aryl oxalate esters for peroxyoxalate chemiluminescence reactions

Abstract: Six oxalate esters of 2-nitro-4-alkoxycarbonylphenol and 2-alkoxycarbonyl-4-nitrophenol were synthesised for use in the peroxyoxalate chemiluminescence reactions that take place via several steps with 4-hydroxy-3-nitrobenzoic acid and 5-nitrosalicylic acid as starting materials, respectively. The addition of ethylene glycol to the alkoxy moiety enhanced the solubility in solvents such as acetone, acetonitrile and ethyl acetate. When reacted with hydrogen peroxide in the presence of a fluorescent compound, perylene, they gave similar chemiluminescence reaction curves to those of DNPO [bis(2,4-dinitrophenyl) oxalate] and TCPO [bis(2,4,6-trichlorophenyl) oxalate]. Among them, bis[4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl] oxalate was found to be the best for the high-sensitivity detection of both hydrogen peroxide and fluorescent compounds using the peroxyoxalate chemiluminescence reaction because of its extreme solubility in solvents such as acetone (767 mM) and acetonitrile (1010 mM).

Flow cell studies with immobilised reagents for the development of an optical fibre sulphide sensor

Abstract: Several reagent systems, such as 2,6-dichlorophenolindophenol, phenanthroline complexes and dithiofluorescein complexes, have been immobilised on polymeric solid supports and their suitability as interphases in optical fibre sensors for sulphide ions investigated. These studies were carried out in a flow cell arrangement. The reflectance of the reagent phase was measured using optical fibres and was found to be related to the concentration of the sulphide ions in the solution. The dynamic range for sulphide ion determination varied with the reagents. The reagent phases prepared from 2,6-dichlorophenolindophenol and from the complex formed by dithiofluorescein with o-hydroxymercuribenzoic acid could be regenerated and are considered suitable for the development of an optical fibre sensor for sulphide ions.

Optimisation in inductively coupled plasma mass spectrometry

Abstract: The performance of a commercial inductively coupled plasma mass spectrometer has been investigated as a function of a number of parameters associated with sample introduction and plasma operation. The forward r.f. power to the plasma and the nebuliser argon pressure are the two that have the greatest effect. For a variety of elements, similar optimum settings for these two variables are found. Optimising the signal due to M+ generally minimises the signal due to M2+ or MO+. Substantial differences between the optima for these variables in ICP-MS compared with ICP-ES are found.

Quantitative determination of thiourea in aqueous solution in the presence of sulphur dioxide by Raman spectroscopy

Abstract: A method has been developed for the quantitative determination of thiourea in aqueous solutions acidified with sulphuric acid in the presence of sulphur dioxide. The method uses laser Raman spectroscopy and is valid in the presence of high concentrations of sulphur dioxide and inorganic salts. This is particularly important with respect to the use of such solutions for the leaching of gold from ores and concentrates. The method is simple, rapid and accurate to within ±1.2% and has been applied to the study of solutions used in leaching experiments.

Determination of aluminium in human tissues and body fluids by Zeeman-corrected atomic absorption spectrometry.

Abstract: A procedure is described for the determination of aluminium in samples of human origin. It is based on Zeeman-corrected atomic absorption spectrometry, and the method of standard additions is used for the quantitation. Plasma and urine samples were analysed directly after dilution and tissue samples after wet digestion with nitric acid. For plasma samples, the precision was approximately 5%(relative standard deviation) at the 50 µg l–1 level, and the accuracy of the method was evaluated by analysing the NBS reference material bovine serum. For tissue samples, the accuracy and precision were determined from recovery experiments. Examples of aluminium concentrations found in human plasma, urine, bone, liver and brain are given.

Simultaneous determination of major and trace elements in urinary calculi by microwave-assisted digestion and inductively coupled plasma atomic emission spectrometric analysis

Abstract: A procedure that permits the simultaneous determination of major, minor and trace elements in urinary calculi by inductively coupled plasma atomic emission spectrometry is described. The dissolution of samples is achieved with a commercial microwave oven using a mixture of nitric and perchloric acids. Ca, Mg, P, Al, Cu, Fe, K, Li, Mn, Mo, Na, Pb, S, Sr and Zn were determined in more than 100 South African stones.

Porous membrane-based diffusion scrubber for the sampling of atmospheric gases

Abstract: A diffusion scrubber, employing a porous fluorocarbon membrane as the sampling tube and with a scrubber solution flowing into a narrow annular space exterior to the membrane, is described. The use of this diffusion scrubber with a dilute buffered formaldehyde solution as the scrubber solution has been exploited for collecting sulphur dioxide. Collection efficiencies are reported for sampling rates of up to 3 l min–1. The response time to a SO2 input pulse in the continuous analysis mode is demonstrated using dilute hydrogen peroxide as the scrubber solution and a conductivity detector. The advantages of a diffusion scrubber for collecting atmospheric gases are discussed. A simple inexpensive design of permeation tubes for standard gas sources is also reported.

Characterisation and evaluation of the use of membrane mimetic agents to amplify chemiluminescence from the lucigenin-hydrogen peroxide reaction system

Abstract: The 10,10′-dimethyl-9,9′-biacridinium dinitrate (lucigenin)-hydrogen peroxide-N-methylacridone chemiluminescence (CL) system was characterised in different types of membrane mimetic agents and homogeneous solvents, and the effects of various membrane mimetic agents on the lucigenin-hydrogen peroxide light reaction were assessed. Aqueous solutions of the surfactants hexadecyltrimethylammonium chloride, 3-(N-dodecyl-N,N-dimethylammonio)propane-1-sulphonate, polyoxyethylene(23)dodecanol, dioctadecyldimethylammonium bromide and α-, β- and γ-cyclodextrin enhanced the CL intensity by factors of up to 3.4, 2.5, 4, 1.6, 2.3, 14 and 12.6, respectively. A lowering of the CL emission was observed in the presence of all anionic surfactant media examined. The various experimental variables that influence the magnitude of the CL enhancements or reductions are briefly described, and the advantages and limitations of these agents as CL enhancers are discussed. The alterations in the CL intensity are rationalised in terms of the effect of these different membrane mimetic agents on the rate of the reaction and/or excitation efficiency. Lastly, the analytical implications and possible advantages of using such membrane mimetic agents in lucigenin chemiluminescent assays are discussed.

Extraction of iron(III), gold(III), gallium(III), thallium(III), antimony(V) and antimony(III) from hydrochloric acid solution with crown ethers

Abstract: Chloroform solutions of dicyclohexyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6) and 18-crown-6 (18C6) efficiently extracted iron(III), gold(III), gallium(III), thallium(III) and antimony(V) from solution in hydrochloric acid. Extraction with 15-crown-5 (15C5) and 12-crown-4 (12C4) was poor. Antimony(III) in the presence of titanium(III) chloride was efficiently extracted only with DC18C6. When tervalent iron, gold, gallium and thallium were extracted from acidic lithium chloride solution, even 15C5 and 12C4 gave good extractabilities. The molar ratio of crown ether to the metal ions, except antimony(III), in the extracted species is probably 1 : 1, and the metals are probably extracted as chloro complexes, e.g., HFeCl4 and LiFeCl4. Iron and gallium in aluminium-base alloys were determined after their separation by DC18C6 extraction.

Determination of vitamin C by flow injection analysis

Abstract: A photometric procedure for the determination of vitamin C using chloramine T by two flow injection analysis (FIA) methods is described. The first is in the presence of potassium iodide-starch solution using the normal FIA technique (linear determination range: 15–150 µg ml–1, RSD ±0.97% and sampling frequency 90 samples h–1) and the second is in the presence of potassium bromide-methyl red solution using an FIA titration (linear determination range: 0.5–1000 µg ml–1, RSD ±0.82% and a sampling frequency of 30 samples h–1). The two methods are compared with each other and with a conventional titration procedure.