Showing papers in "Analyst in 1982"

Determination of the non-starch polysaccharides in plant foods by gas-liquid chromatography of constituent sugars as alditol acetates

Abstract: A method is reported for the measurement of non-starch polysaccharides (NSP) from plant foods. NSP are the major components of “dietary fibre.” The polysaccharides are divided into cellulose and non-cellulosic material and the constituent sugars are determined by gas-liquid chromatography. Starch is removed, after gelatinisation, by incubation with hog pancreatic α-amylase together with pullulanase. The enzyme preparations are shown to be specific for the hydrolysis of α-1,4- and α-1,6-glucosidic bonds, and not to affect NSP. The starch-free material is then analysed by three separate but complementary procedures: (A) hydrolysis with 1 M sulphuric acid after solubilisation of cellulose with 12 M sulphuric acid; (B) hydrolysis with 1 M sulphuric acid; and (C) extraction with phosphate buffer at pH 7 and 100 °C, solubilisation of cellulose with 12 M sulphuric acid and then hydrolysis with 1 M sulphuric acid. Neutral sugars are measured by gas-liquid chromatography as alditol acetates and uronic acids by a colorimetric method. Starch made resistant to α-amylase digestion by food processing is identified by additional steps in procedure B, and measured as “resistant starch.” Procedure A gives total NSP and procedure B neutral non-cellulosic polysaccharides. A value for cellulose is obtained as the difference between glucose measured in procedures A and B. Procedure C gives NSP insoluble in phosphate buffer at pH 7. Soluble NSP is the difference between total NSP and insoluble NSP. Results for the NSP analysis of selected foods are given.

Spectrophotometric assay of clavulanic acid by reaction with imidazole

Abstract: An assay method for salts of clavulanic acid is based on the absorbance at 312 nm of the product of reaction with imidazole. The reaction product has been isolated and identified as 1-(4-aza-8-hydroxy-6-oxo)oct-2-en-1-oylimidazole. The method is applicable to clavulanate concentrations of down to about 2 µg ml–1 and is specific for intact clavulanate in the presence of degradation products. Derivatives of clavulanic acid and other compounds containing the clavam nucleus also give strongly absorbing products under the assay conditions, but penicillins give little or no absorbance.

Critical evaluation of a multi-element scheme using plasma emission and hydride evolution atomic-absorption spectrometry for the analysis of plant and animal tissues

Abstract: An analytical scheme that uses inductively coupled argon plasma emission spectroscopy (ICAP) and hydride evolution atomic-absorption spectrometry (HEAA) for the determination of trace elements in plant and animal tissues has been evaluated. The scheme incorporates the ion-exchange procedure of Kingston et al., which uses Chelex 100 resin to concentrate trace elements and remove potentially interfering alkali and alkaline earth metals. The separation procedure is included in a scheme designed to maximise the number of analyte metals that can be determined from a single digestion of a biological matrix. Acid-digested samples are divided into two fractions. One fraction (5% of the total) is measured directly by ICAP for alkali and alkaline earth metals and phosphorus and for transition metals such as iron and manganese, which are not well behaved on the resin. The other fraction (95% of the total) is subjected to the separation procedure whereby a number of biologically important trace elements, including cadmium, copper, molybdenum, nickel, vanadium and zinc, are initially sequestered by the resin, and then stripped into a small volume of dilute nitric acid for ICAP measurement of the “matrix-free” analytes. Arsenic, selenium and antimony, which are not retained by the resin, are collected with the initial column effluent, acidified and determined by HEAA. The reliability of the scheme is influenced by the nature of the acid digestion procedure used to oxidise the organic matrix. The scheme was tested by analysis of ten National Bureau of Standards biological reference materials.

Determination of iron in natural waters and plant material with 1,10-phenanthroline by flow injection analysis

Abstract: A flow injection analysis procedure for the determination of total iron in natural waters and plant digests by the 1,10-phenanthroline method is described. Effects of mixing-coil lengths, sample volume, flow-rates, reagent concentrations and interfering species were investigated. The proposed procedure allows the determination of iron concentrations in the range 0.1–30 p.p.m. at a rate of up to 180 samples per hour with a relative standard deviation of lower than 1%. The results agree with those obtained by atomicabsorption spectrometry, and an iron concentration identical with the certified value was found by analysis of an NBS standard reference material.

Regression methods in the comparison of accuracy

Abstract: Monte Carlo simulation has been used to test the robustness of three methods of regression in the comparison of analytical accuracy. The methods used were simple linear regression, weighted linear regression and a new method based on maximum likelihood estimation. The new method is capable of unbiased estimation with different heteroscedastic variance of both the y-values and the x-values, and is the most generally useful. However, even simple linear regression can estimate linear biases accurately as long as elementary safeguards are applied. The simulations realistically covered a wide range of circumstances likely to be encountered in analytical practice.

A study of pneumatic nebulisation systems for inductively coupled plasma emission spectrometry

Abstract: The analytical performance of different pneumatic nebulisers and cloud chambers for inductively coupled plasma emission spectrometry is reported. A vortex cloud chamber and a double-pass cloud chamber were compared for use with concentric glass nebulisers. An all-plastic double-pass cloud chamber was preferred. Two new nebulisers for solutions containing high levels of dissolved solids or slurries are described. One of these, machined entirely from inert plastic, gave an improved performance compared with a glass concentric nebuliser and no problems were encountered with the nebulisation of solutions containing 20%m/V of dissolved solids or slurries.

Micellar enhanced fluorimetric determination of 1-NN-dimethylaminonaphthalene-5-sulphonyl chloride and o-phthalaldehyde-2-mercaptoethanol derivatives of amino acids

Abstract: The effects of various surfactant micellar systems upon the spectrofluorimetric method for the determination of amino acids by Roth's method and the dansyl chloride procedure have been assessed. Specifically, the fluorescence intensity of dansyl glycine was found to be remarkably enhanced when in the presence of cationic hexadecyltrimethylammonium chloride or dodecyltrimethylammonium chloride and zwitterionic N-dodecyl-NN-dimethylammonium-3-propane-1-sulphonic acid micellar systems. Likewise, the lysine derivative of o-phthaladehyde-2-mercaptoethanol exhibited intensified fluorescence when in the presence of non-ionic Brij-35 or Triton X-100 and anionic sodium dodecylsulphate micelles. Depending upon the type of surfactant micellar system employed, fluorescence enhancements of from 8 to 20 were observed in comparison with that in water alone. Owing to this micellar phenomenon, the sensitivity of the fluorimetric methods for the determination of these two species was correspondingly increased from 8- to 20-fold over the conventional procedures.The spectral parameters, quantum yields, lower detection limits and analytical figures of merit for these two substances in the micellar systems and water alone are compared. Possible reasons for this observed micellar induced enhanced fluorescence are given. A brief prospective on the general applicability of using micelles to enhance other fluorimetric methods is also given.

Determination of selenium in biological samples by hydride generation and atomic-absorption spectroscopy.

Abstract: Hydride generation followed by atomic-absorption spectroscopy has been used to determine the concentrations of selenium in 100-µl volumes of whole blood, plasma and erythrocyte suspensions following digestion of the samples with nitric and sulphuric acids. Analyses of human and animal sera agreed well with those obtained by other workers for selenium concentrations in the range 6–160 µg l–1. Relative standard deviations of 4.0–4.5% were obtained for replicate analyses of human plasma and whole blood containing selenium at concentrations of 120–144 µg l–1.

Volatilisation of some elements from a graphite rod direct sample insertion device into an inductively coupled argon plasma for optical emission spectrometry

Abstract: Further preliminary studies of analytical performance are described for the use of a graphite rod direct sample insertion device for inductively coupled plasma optical emission spectrometry. The volatilisation of uranium, zirconium, titanium, molybdenum, boron, chromium, zinc, silver and copper from this direct sample insertion device is discussed; the use of an argon-0.1% Freon 23 mixture as injector gas permits the efficient volatilisation of refractory carbide-forming elements. Using this mixture, improvements in the detection limits of more than two orders of magnitude have been obtained for uranium, zirconium and titanium.

Optical emission spectrometry with an inductively coupled radiofrequency argon plasma source and direct sample introduction from a graphite rod

Abstract: Preliminary studies of analytical performance are described for an instrumental assembly in which microlitre volumes of liquid samples are applied to a graphite rod, desolvated and the rod is inserted axially directly into a continuously operating low-power inductively coupled argon plasma. Simplex optimisation of operating parameters has been undertaken for manganese to determine the most favourable signal to background intensity ratios and detection limits are reported for manganese, cadmium, cobalt, copper, iron, nickel and lead.

Comparative study of glassy carbon as an electrode material

Abstract: There have often been contradications reported in regard to the efficacy of glassy carbon in voltammetric applications. The problem stems from the fact that there are a large variety of carbons available from various manufacturers that vary in their bulk structure, particularly in the degree of compactness. The extent of compactness affects both the bulk and surface properties of glassy carbon. The latter has a bearing on the formation of surface carbon-oxygen functionalities, which influence the electrochemical response of the carbon.

Rapid determination of residual chlorine by flow injection analysis

Abstract: Flow injection determination of residual chlorine in solution has been carried out spectrophotometrically by methyl orange decolorisation and by formation of a yellow complex with o-tolidine. The carrier streams are 0.180 mM methyl orange in pH 2 buffer solution or 0.01 M hydrochloric acid, and 3.0 mMo-tolidinium dichloride (in 2 M hydrochloric acid), respectively. A sampling rate of 288 samples per hour has been obtained with the latter reagent and the detection limit is 0.08 p.p.m. of chlorine. Influence of flow parameters such as flow-rate, tube length and diameter and the effect of interferents on the determination have been investigated. A study of the hyprochlorite-ammonium-o-tolidine reaction system has been performed and a method for the simultaneous determination of NH4+ and OCl– is described.

Study of some systematic errors during the determination of the total selenium and some of its ionic species in biological materials

Abstract: A method using nitric acid alone for the digestion of biological materials for the determination of total selenium or of some of its ionic species leads to erroneous results because of incomplete mineralisation of some organic selenium compounds, including the selenonium derivatives, the main metabolites of the element in urine, and a selenoamino acid present in plant and animal tissues; such a method also suffers from many interferences owing to the presence of incompletely digested organic constituents of the sample. The use of perchloric acid under certain conditions and of sulphuric acid, in conjunction with nitric acid, leads to an excellent recovery of the selenium added to biological materials or included in organic selenium compounds. The nitric acid method, the only one which affords a selective determination of some selenium ionic species in aqueous solution, has been critically examined but its efficiency cannot be improved; all of the parameters investigated are helpful, however, in choosing an adequate digestion procedure for the determination of the total selenium content of a complex sample.

Rapid flow analysis with inductively coupled plasma atomic-emission spectroscopy using a micro-injection technique

Abstract: An introduction system for liquid micro-samples in inductively coupled plasma atomic-emission spectroscopy is described that allows the injection of 5–500-µl volumes into a rapidly flowing carrier reagent stream leading to the nebuliser. The effect on analyte signal was studied as a function of flow-rate, injection volume and sample concentration. It is shown that the carrier flow-rate determines the response time, sensitivity, precision and sample carry-over in the nebuliser. By the use of relatively rapid flow-rates of up to 7.5 ml min–1, fast injection of 10-µl samples is achieved at an injection rate of 240 h–1 with a relative standard deviation of 1.5% for a single-element analogue readout. Digital readout is used for multi-element determinations with similar or better precision. Detection limits of the order of 0.1 mg l–1 are obtained for 10-µl injections, limited by the volume injected, with a proportionate decrease in detection limit for increasing volumes.

Assay of ephedrine or pseudoephedrine in pharmaceutical preparations by second and fourth derivative ultraviolet spectrophotometry

Abstract: Rapid second and fourth derivative ultraviolet spectrophotometric assay procedures are described for the determination of ephedrine or pseudoephedrine in pharmaceutical formulations. The methods have been applied successfully to Ephedrine Elixir BP, Ephedrine Hydrochloride Tablets BP, Ephedrine Nasal Drops BPC, Paediatric Belladonna and Ephedrine Mixture BPC, tablets and capsules containing aminophylline and amylobarbitone and coloured syrups containing triprolidine hydrochloride and codeine phosphate. A simple solvent extraction stage avoids interference from the co-formulated drugs and colouring agents in certain of the formulations. The specificity, accuracy and precision of the methods have been assessed.

Determination of residues of synthetic pyrethroids in fruit and vegetables by gas-liquid and high-performance liquid chromatography

Abstract: A multi-residue method for the determination of synthetic pyrethroids in fruit and vegetables is presented. After extraction with hexane-acetone, the pyrethroids are separated from co-extractives by a partition process and chromatography on a silica gel column and quantitatively determined by electron-capture gas-liquid chromatography and/or high-performance liquid chromatography using an ultraviolet spectrophotometric detector.

Determination of methylmercury in fish by high-performance liquid chromatography

Abstract: A method has been developed that uses a simplified sample preparation procedure and atomic absorption or electrochemical detection of HPLC eluents for the determination of methylmercury in fish. Methylmercury is isolated from the blended sample by chloroform elution from a diatomaceous earth-hydrochloric acid column. The organomercury compound is then extracted into a small volume of 0.01 N sodium thiosulphate solution. An aliquot of this solution is injected on to a Zorbax ODS column and eluted with methanol-ammonium acetate solution (3 + 2) buffer, pH 5.5 containing mercapto-ethanol. Detection can be accomplished by atomic-absorption spectrophotometry with the aid of a specially designed apparatus for the generation of mercury vapour. Alternatively, a commercially available electrochemical detector equipped with a dropping-mercury electrode may be used.

Development and optimisation of atom cells for sensitive coupled gas chromatography-flame atomic-absorption spectrometry

Abstract: The development of four novel atom cells for the determination of volatile organometallic compounds by coupled gas chromatography-flame atomic-absorption spectrometry is described. Tetraalkyllead compounds provided a model system in the optimisation of the four atom cells by the variable step-size simplex method. The effects of the various parameters on analytical performance are discussed. In the most sensitive system presented the effluent from the chromatograph was fed to a small hydrogen diffusion flame and the atoms from this flame were swept into a flame-heated ceramic tube. This simple, readily demountable arrangement enjoys the advantages of continuous operation associated with flames but, because of the relatively long atomic residence times, gave detection limits of 17 pg for both tetraethyl- and tetramethyllead. These limits are superior to any previously reported for a gas chromatographic-atomic-absorption spectrometric technique, including those employing electrothermal atomisation.

Formation of ternary complexes of aluminium with some triphenylmethane reagents and cationic surfactants

Abstract: The conditions for the formation of ternary complexes of aluminium with Eriochrome Cyanine R (ECR), Chrome Azurol S (CAS) or Pyrocatechol Violet (PV), in the presence of zephiramine, cetyltrimethylammonium (CTA) or cetylpyridinium (CP) ions have been examined. In the systems aluminium-ECR/CAS-zephiramine/CTA/CP, the complexes formed (at pH 5–7) have molar absorptivities of 1.1–1.2 × 105 l mol–1 cm–1, which can form the basis of sensitive spectrophotometric methods. The systems involving PV and cationic surfactants are unsuitable for spectrophotometric methods. The molar ratio of ECR/CAS to aluminium in the ternary complexes is slightly higher than 2 : 1. The recommended method based on the aluminium-ECR-zephiramine system has been applied to the determination of aluminium in river water.

Determination of zinc and copper in isolated leucocytes

Abstract: A procedure is described and evaluated for isolating leucocytes from 15 ml of whole blood using a modified dextran sedimentation procedure. The mean recovery of leucocytes is 62% without differential white cell loss, and there is no contamination from red cells, platelets or plasma. Digestion of leucocytes with nitric acid is performed prior to the determination by atomic-absorption spectrophotometry of zinc using flame atomisation and of copper by electrothermal atomisation. The relative standard deviations for the determinations range between 2.2 and 3.6%. The range reported for zinc in leucocytes is 68–246 pmol per 106 cells and 4.1–36.8 per 106 cells for copper. These results are compared with those from other studies.

Determination of metal ions by liquid chromatography incorporating dithiocarbamates in the eluent

Abstract: Dilute solutions of transition metal ions, including copper(II), cobalt(II), nickel(II), lead(II) and iron(III), can be determined using reversed-phase liquid chromatography on Hypersil ODS by direct injection into an eluent containing sodium diethyldithiocarbamate (0.05%m/V). The complexes formed are detected using a variable wavelength detector. The effects of reagent concentration, flow-rate and pH have been examined.

Determination of germanium in coal ashes by hydride generation and flame atomic-absorption spectrophotometry

Abstract: This paper describes the determination of germanium by atomic-absorption spectrophotometry with direct introduction into a dinitrogen oxide-acetylene flame of the germanium(IV) hydride generated by reducing with sodium tetrahydroborate(III) solution. A comparative study of the sensitivity of the germanium determination has been carried out and a study of interferences from lead(II), arsenic(III) and -(V), iron(II) and -(III), tellurium(IV), selenium(IV), antimony(III), tin(II), tartrates, oxalates and fluorides is described. The sensitivity of the proposed method is 0.012 µg ml–1 and the detection limit is approximately 100 times better than obtained with silica tube atomisation at a wavelength of 265.14 nm. The method has been applied to the determination of germanium in lignite ashes with an average germanium recovery of 97.65% and a relative standard deviation of 2.87%.

Rapid hydride evolution - electrothermal atomisation atomic-absorption spectrophotometric method for determining arsenic and selenium in human kidney and liver.

Abstract: A rapid semi-automated electrothermal atomisation atomic-absorption spectrophotometric procedure has been developed for the determination of arsenic and selenium in human liver and kidney specimens. The sample is digested with a mixture of nitric and perchloric acids. The nearly dry residue is taken up in hydrochloric acid. The arsenic or selenium in the hydrochloric acid solution is converted into its hydride with sodium tetrahydroborate(III). The hydride is decomposed and atomised in an electrically heated silica furnace, and the atomic-absorption signal is measured at the appropriate resonance wavelengths of arsenic and selenium. Both of the elements can be determined in the biological samples in the range 50–500 ng per gram of wet sample. The method was applied to the determination of arsenic and selenium in about 40 autopsy samples of human kidney (cortex and medulla) and liver taken from Canadian adults living in the Great Lakes Region of Ontario. The arsenic levels in all of the samples analysed were found to be ⩽ 10 ng per gram of wet sample; the median selenium levels in the cortex, medulla and liver were found to be 0.84, 0.31 and 0.39 mg per kilogram of wet sample, respectively.

Flow injection voltammetric determination of phosphate: direct injection of phosphate into molybdate reagent

Abstract: Phosphate can be determined precisely as molybdophosphate by flow injection analysis using a glassy carbon electrode as a voltammetric detector. The sample solution (25 µl, 1 × 10–6–5 × 10–4M in phosphate) is injected into an eluent which is 2%m/V in ammonium molybdate and 0.6%V/V in concentrated sulphuric acid. Molybdophosphate, which is determined by reduction at the glassy carbon electrode, is fully formed when a 3-m delay coil (0.58 mm i.d.) is incorporated before the detector and a flow-rate of 4 ml min–1 is used.

Kinetic determination of nitrite in waters by using a stopped-flow analyser

Abstract: Automatic kinetic methods for the determination of nitrite in waters with a stopped-flow analyser are described. The methods are based on the diazotisation of sulphanilamide, the product being coupled with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a highly coloured azo dye, which is measured at 540 nm. A single-point kinetic procedure uses a delay time of 10 s and one measurement of 0.7 s. A multi-point reaction rate method uses a delay time of 0.8 s and a measurement time of 1.5 s. The methods are fast, sensitive, accurate and precise, and without serious interference. The sample throughput for routine analysis can be up to 360 samples per hour in the range 0.025–2.00 p.p.m. of nitrite-nitrogen.