Showing papers in "Analyst in 1990"
TL;DR: In this article, high-temperature gas chromatography (GC) and GC-MS were used to extract organic residues from materials of archaeological interest by solvent extraction and subjected directly to hightemperature GC.
Abstract: Organic residues are extracted from materials of archaeological interest by solvent extraction and subjected directly to high-temperature gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The use of high-temperature GC allows intact acyl lipids, e.g., triacylglycerols, diacylglycerols, monoacylglycerols and wax esters, to be analysed without prior degradation (e.g., saponification) to release constituent fatty acids and alcohols. Trimethylsilylation is employed to block protic sites in free fatty acids and hydroxylated components. The data obtained from temperature programmed GC and GC-MS analyses, employing immobilised apolar (dimethyl polysiloxane type) stationary phases, provide essential compositional information that would be lost if the more conventional degradative approach to acyl lipid analysis was adopted.
271 citations
TL;DR: Some recent developments in analytical solution chemiluminescence (CL) are described in this paper, including various approaches for monitoring CL, especially flow injection, applications based on luminol and peroxyoxalate CL, direct determinations based on the CL of the analyte, and the uses of CL for liquid chromatographic detection.
Abstract: Some recent developments in analytical solution chemiluminescence (CL) are described. These include various approaches for monitoring CL, especially flow injection, applications based on luminol and peroxyoxalate CL, direct determinations based on the CL of the analyte, and the uses of CL for liquid chromatographic detection.
118 citations
TL;DR: In this article, 3-Methyl-1-phenyl-4-stearoyl-5-pyrazolone loaded on to silica gel was used as a pre-concentration reagent for copper, cobalt and nickel prior to atomic absorption spectrometric determination.
Abstract: 3-Methyl-1-phenyl-4-stearoyl-5-pyrazolone loaded on to silica gel was used as a pre-concentration reagent for copper, cobalt and nickel prior to atomic absorption spectrometric determination. Both batch and column methods were used for the concentration of the above metals. These metals are quantitatively retained on the proposed adsorbent above pH 4. The adsorption-elution cycle can be repeated ten times with no observable decline in the efficiency of the adsorbent. As there are no observable effects due to changes in the volume of sample solution up to a volume of 1 l, a concentration factor of 40 can be achieved. The method has been applied to samples of sodium chloride solution and tap water.
106 citations
TL;DR: For all elements significantly above the detection limit and reagent blank concentrations, good agreement exists between ICP-MS and certified values.
Abstract: A procedure has been developed for the analysis of biological materials by inductively coupled plasma mass spectrometry (ICP-MS). Fast, efficient and complete sample digestion is achieved by a combined microwave-nitric acid/open beaker-nitric acid-hydrogen peroxide procedure. The ICP-MS analysis is performed with an on-line five-element internal standard to correct for matrix and instrumental drift effects. Results are presented for 24 elements in three biological reference materials (National Institute of Standards and Technology Standard Reference Materials 5277a Liver and 1566 Oyster and International Atomic Energy Agency Certified Reference Material H4 Animal Muscle). For all elements significantly above the detection limit and reagent blank concentrations, good agreement exists between ICP-MS and certified values.
104 citations
TL;DR: In this paper, a potentiometric selectivity study has been made using two esters containing hexameric calix[6]arenes, p-tert-butyl hexaethyl ester (1a) and the unsubstituted hex aethyl esters (1b), as the ionophores for caesium ions.
Abstract: Hexameric calix[6]arene ester compounds have shown an ability to extract large alkali metal ions such as caesium and rubidium in phase transfer studies A potentiometric selectivity study has been made using two ester containing hexameric calix[6]arenes, p-tert-butyl hexaethyl ester (1a) and the unsubstituted hexaethyl ester (1b), as the ionophores for caesium ions Six electrodes were prepared with 2-nitrophenyl octyl ether as the solvent mediator and various amounts of potassium tetrakis(p-chlorophenyl)borate as the ion exchanger in a poly(vinyl chloride) matrix The ligands examined produced electrodes with near-Nernstian slopes; the selectivity coefficients for caesium with respect to rubidium, potassium, sodium, lithium, calcium, magnesium, hydrogen and ammonium were determined Lifetimes of at least 1 month were estimated
95 citations
TL;DR: The simultaneous determination of iodine and bromine in plasma and urine by inductively coupled plasma mass spectrometry, using a Nermag prototype instrument, is described, and results are in agreement with reported values.
Abstract: The simultaneous determination of iodine and bromine in plasma and urine by inductively coupled plasma mass spectrometry, using a Nermag prototype instrument, is described. The sample preparation involves only a 10-fold dilution with a diluent containing europium as an internal standard followed by direct nebulisation in the plasma. The iodine, bromine and europium ions are measured at m/z= 127, 79, and 153, respectively. The sensitivity of the method, with detection limits of 1.6 and 52 µg l–1 for iodine and bromine, respectively, is satisfactory for clinical applications. The calibration graphs were linear over the ranges 0–400 µg l–1 and 0–40 mg l–1 for iodine and bromine, respectively, which are wide enough for most assays. The recoveries were close to 100% with coefficients of variation of less than 3%. The within-day and between-day reproducibility was about 5%. The concentrations of iodine and bromine in the plasma of 26 healthy individuals were 58 ± 12 µg l–1 and 4.1 ± 0.9 mg l–1, respectively. The amounts of iodine and bromine eliminated in urine were 94 ± 97 µg per 24 h (range 27–403 µg per 24 h) and 3.6 ± 1.7 mg per 24 h, respectively. These results are in agreement with reported values.
93 citations
TL;DR: The concentrations of Cd, Co, Cr, Fe, Mo, Ni, Se, Ti, V and Zn in biological fluids, human blood serum and market milk were determined by neutron activation analysis, with enrichment by coprecipitation.
Abstract: The concentrations of Cd, Co, Cr, Fe, Mo, Ni, Se, Ti, V and Zn in biological fluids, human blood serum and market milk were determined by neutron activation analysis, with enrichment by coprecipitation. The pre-concentration of these trace elements was accomplished by converting the dissolved trace metal ions into their pyrrolidinedithiocarbamate (1-pyrrolidinecarbodithioate) chelates, followed by coprecipitation with a metal carrier such as Ni, Pb or Bi. The coprecipitation was carried out prior to irradiation for the short-lived nuclides (V, Ti and Se) and after irradiation for the other elements. The validity of the method was checked using certified biological reference materials; the concentrations of trace elements found by the proposed method agreed well with the published certified data. The limits of detection for Cd, Co, Cr, Fe, Mo, Ni, Se (obtained through the long-lived isotope 75Se) and Zn under the present experimental conditions were found to be 5, 5, 10, 520, 5, 70, 10 and 150 ng, respectively, for 5 ml of biological liquor. The limits of detection for Ti and V obtained (through their short-lived radionuclides 51Ti and 52V, respectively) were found to be 180 and 1.4 ng, respectively, for 50 ml of market milk, or 70 and 0.7 ng for 1 ml of blood serum.
85 citations
TL;DR: Ascorbate oxidase was immobilised on cyanogen bromide activated-Sepharose 4B and incorporated in a flow-injection system with amperometric detection at a glassy carbon electrode at +0.6 V for the simple and rapid determination of L-ascorbic acid in fruit and vegetable juice.
Abstract: Ascorbate oxidase was immobilised on cyanogen bromide activated-Sepharose 4B and incorporated in a flow-injection system with amperometric detection at a glassy carbon electrode at +0.6 V. On passage through the immobilised ascorbate oxidase a fraction of the L-ascorbic acid was converted into dehydroascorbic acid and the decrease in signal was measured. This could be directly related to the amount of L-ascorbic acid present. The calibration graph was linear over the range 0-400 ng ml(-1) with a correlation coefficient of 0.9994. The detection limit (2 sigma) in phosphate buffer (0.08 M, pH 5.5) was 4.0 ng ml(-1). The relative standard deviation for a 200 ng ml(-1) standard was 1.0% (n = 10) and the sampling throughput was 30 samples h(-1). The method was used for the simple and rapid determination of L-ascorbic acid in fruit and vegetable juice.
81 citations
TL;DR: In this article, yeast cells were used as a model system for the investigation and identification of toxic forms of vanadium obtained on dosing a nutrient medium with various known vanadium species.
Abstract: Yeast cells were used as a model system for the investigation and identification of toxic forms of vanadium obtained on dosing a nutrient medium with various known vanadium species. Total vanadium uptake by the yeast cells was in the region of 10 p.p.m. when the nutrient medium was dosed with 200 p.p.m. of the toxic species VV prepared as a V2O5-NaOH solution. No cell growth was observed in the nutrient medium when the concentrations were above 200 p.p.m. However, vanadium was found to accumulate in the yeast cells to a much greater extent when the nutrient medium was dosed with solutions of the less toxic form VIV. Total vanadium in the cells was determined using flame atomic absorption spectrometry.
79 citations
TL;DR: Cholesterol is resolved from the principal plant phytosterols, while the tocopherol congeners are well separated, thereby offering complementary information regarding source-lipid composition in foods under regulatory quality-control conditions.
Abstract: A method is described for the simultaneous determination of cholesterol, phytosterols and tocopherols in dairy and non-dairy foods by high-performance liquid chromatography. A facile saponification and extraction scheme is completed rapidly within a single reaction tube. Clean-up is not required, with analysis completed by one of two alternative reversed-phase approaches. Sterols are monitored by short-wave ultraviolet spectrophotometry, and tocopherols by means of a series fluorescence detector. Cholesterol is resolved from the principal plant phytosterols, while the tocopherol congeners are well separated, thereby offering complementary information regarding source-lipid composition in foods under regulatory quality-control conditions. Squalene, an essential metabolic sterol precursor, can also be determined concurrently at the same viewing wavelength.
67 citations
TL;DR: A rapid and precise continuous-flow method for the determination of isoniazid based on the chemiluminescence produced during its reaction with N-bromosuccinimide in alkaline medium demonstrates good accuracy and precision.
Abstract: A rapid and precise continuous-flow method is described for the determination of isoniazid (0050–200 µg ml–1) based on the chemiluminescence produced during its reaction with N-bromosuccinimide in alkaline medium The emission intensity is greatly enhanced by the presence of ammonia The procedure is automated and samples can be analysed at a rate of 112 solutions per hour with a relative error of about 2% When applied to tablets, the method is relatively free from interferences from common excipients and co-existing compounds The results obtained for the assay of commercial preparations compared well with those obtained by an official chemical method and demonstrated good accuracy and precision
TL;DR: In this paper, a semi-micro modification of the dichromate method for the determination of low concentrations (1 − 35 mg l − 1) of the chemical oxygen demand is described.
Abstract: A semi-micro modification of the dichromate method for the determination of low concentrations (1–35 mg l–1) of the chemical oxygen demand is described. It is based on the experimentally established dependencies of the oxidation efficiency on the concentrations of H2SO4, K2Cr2O7 and Ag2SO4, and on the temperature and time of heating. The procedure involves increasing the concentration of H2SO4 and heating in closed test-tubes in a heating block at 170 °C for 40 min and the spectrophotometric determination of dichromate at 455 nm. The interfering effect of chloride, up to a concentration of 100 mg l–1, is masked by using a combination of HgSO4 and KCr(SO4)2. The modification has been tested on 30 samples of ground, tap, precipitation and surface waters and on 16 chemical compounds, and gives results comparable to those from a standard reflux method.
TL;DR: In this paper, a group of amides and oxamides has been used as potential ionophores for lead ions in solvent polymeric membrane electrodes, and the most favourable analytical results (slope, log kPb,M and lifetime) were obtained with membranes incorporating ionophore ETH 295 and potassium tetrakis(p-chlorophenyl)borate.
Abstract: A group of amides and oxamides has been used as potential ionophores for lead ions in solvent polymeric membrane electrodes. The most favourable analytical results (slope, log kPb,M and lifetime) were obtained with membranes incorporating ionophore ETH 295 and potassium tetrakis(p-chlorophenyl)borate. With the use of these membranes: (i) a linear response with a slope of 35.3 mV per pPb unit in PbII and an activity range of 10–5.2–10–1.0M were obtained; (ii) the selectivity factors (log kPb,M) were lower than –1.5 with respect to the ions studied (with the exception of Ag+ and H+ ions); (iii) the electrodes can be used with no change in their properties for at least 2 months.
TL;DR: The development of a carbon paste-tetrathiafulvalene amperometric enzyme electrode for the determination of glucose in flowing streams is described and high accuracy can be obtained under SS conditions.
Abstract: The development of a carbon paste-tetrathiafulvalene amperometric enzyme electrode for the determination of glucose in flowing streams is described. The enzyme electrode is operated in a flow-through detector based on the wall-jet configuration under flow injection (Fl) and steady-state (SS) conditions. Under Fl conditions, high precision (0.6%) and sample throughput (120 samples h–1) are possible. Moreover no pre-conditioning of the electrode is required. The flow system is suitable for the determination of glucose in whole blood without sample dilution. With proper orientation of the jet with respect to the enzyme electrode, high accuracy can be obtained under SS conditions.
TL;DR: In this article, a pre-column chelating agent for the determination of trace metal ions by reversed-phase high-performance liquid chromatography (RP-HPLC) with spectrophotometric detection was examined.
Abstract: 2,2′-Dihydroxyazobenzene and five substituted analogues have been examined as pre-column chelating agents for the determination of trace metal ions by reversed-phase high-performance liquid chromatography (RP-HPLC) with spectrophotometric detection. Seven metal ions, viz., AlIII, CoIII, CuII, FeIII, MoVI, VV and ZnII, were detected as their azo chelates in the ion-pair RP mode. The optimum conditions, including pH for colour formation, column used, mobile phase parameters and detection wavelength, were investigated for each individual reagent. The method was applied to the determination of Al and Fe in coal fly ash samples. The kinetic nature and the forms of the chelates responsible for the selectivity of RP-HPLC towards metal ions are discussed in terms of “kinetic differentiation” together with ion-pair RP partition phenomena.
TL;DR: By using different formats of ELISA, it is demonstrated that different responses can be obtained for heat-processed meat versus processed offal, and that determination of a species meat content in a cooked mixed meat product is possible.
Abstract: An overview of developments that have occurred in meat species identification over the last decade is presented. It starts by noting the different requirements for speciation techniques over the period, describes the complex nature of meat in terms of chemical composition and shows how the chain of events from slaughter to retail gives rise to opportunities for deliberate adulteration or innocent contamination. The limitations of techniques such as electrophoresis and isoelectrofocusing are pointed out where the analysis of mixed meats is concerned; attention then focuses on the range of techniques based on antigen-antibody interactions: agar gel immunodiffusion, counter immuno-electrophoresis and enzyme-linked immunosorbent assay (ELISA) in three formats. The choice of analyte is discussed, firstly for the analyses of raw meat materials and secondly, for heat-processed meat products. In the first example, blood serum proteins are used almost exclusively despite the limitation that their presence does not necessarily denote the presence of the corresponding muscle tissue (meat). For cooked products, a new range of antisera are necessary, based on thermally stable components derived from the tissues. By using different formats of ELISA, it is demonstrated that different responses can be obtained for heat-processed meat versus processed offal, and that determination of a species meat content in a cooked mixed meat product is possible. Techniques for improving the specificity and performance of antisera are discussed briefly, with the future introduction of thermally stable, muscle-specific monoclonal antisera being seen as the way forward.
TL;DR: In this article, aldehydes and ketones were synthesized using 4aminosulphonyl-7-hydrazino-2,1,3-benzoxadiazole (ABD-H) and 4-(N,N-dimethylaminosulphl)-7,7,hydrazin-7, hydrazino hydrazine (NBD-H).
Abstract: Fluorogenic reagents for aldehydes and ketones, viz., 4-aminosulphonyl-7-hydrazino-2,1,3-benzoxadiazole (ABD-H) and 4-(N,N-dimethylaminosulphonyl)-7-hydrazino-2,1,3-benzoxadiazole (DBD-H) and also purified 4-hydrazino-7-nitro-2,1,3-benzoxadiazole hydrazine (NBD-H.NH2NH2) were synthesised. These reagents are not fluorescent; however, their reaction products with aldehydes and ketones fluoresce at wavelengths from 548 to 580 nm with excitation from 450 to 470 nm. Both ABD-H and DBD-H exhibited similar reactivity and were more reactive than NBD-H.NH2NH2. The respective pseudo-first-order reaction rate constants for the production of the hydrazone of propionaldehyde with ABD-H, DBD-H and NBD-H.NH2NH2 were 8.9 × 10–2, 7.2 × 10–2 and 4.2 × 10–2 min–1(the reaction was carried out in 0.0025% trifluoroacetic acid in acetonitrile at room temperature, 22 °C). The detection limits using the manual method (i.e., measurement of fluorescence intensity) for the hydrazones of aldehydes and ketones with ABD-H, DBD-H and NBD-H.NH2NH2 were in the µM range. The substrate blank fluorescence with ABD-H was half of that with DBD-H and NBD-H.NH2NH2. The reaction products were separated and analysed by reversed-phase high-performance liquid chromatography (HPLC) with spectrofluorimetric detection. The detection limits for propionaldehyde were 1040, 120 and 35.0 fmol with ABD-H, DBD-H and NBD-H.NH2NH2, respectively, and those for heptan-4-one were 2690, 560 and 673 fmol, respectively. Of the three reagents, DBD-H is recommended for the sensitive detection of ketones and NBD-H.NH2NH2 for the detection of aldehydes. The detection limits for aldehydes and ketones by HPLC were in the sub-pmol to pmol range.
TL;DR: The simultaneous determination of salicylic acid in binary and/or ternary mixtures and its two main urinary metabolites is proposed.
Abstract: The simultaneous determination of salicylic acid in binary and/or ternary mixtures and its two main urinary metabolites is proposed. Mixtures of salicylic, salicyluric and gentisic acids are resolved by synchronous spectrofluorimetry, in combination with first-derivative measurements. The urine is extracted with diethyl ether in acid medium. Salicylic and salicyluric acids are re-extracted into glycine-sodium hydroxide buffer solution of pH 11.6 and determined at that pH, and salicylic and gentisic acids are re-extracted into boric acid-sodium hydroxide buffer solution of pH 8.5 and determined at pH 6.
TL;DR: In this article, 6,7-Dimethoxy-1-methyl-2(1H)-quinoxalinone-3-propionylcarboxylic acid hydrazide was found to be a highly sensitive fluorescence derivatisation reagent for carboxyl acids in high-performance liquid chromatography.
Abstract: 6,7-Dimethoxy-1-methyl-2(1H)-quinoxalinone-3-propionylcarboxylic acid hydrazide was found to be a highly sensitive fluorescence derivatisation reagent for carboxylic acids in high-performance liquid chromatography. The reaction conditions were optimised for various C5–C20 saturated fatty acids. The reagent readily reacted with the fatty acids in aqueous solution in the presence of pyridine and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide at room temperature to produce the corresponding fluorescent derivatives, which were separated on a reversed-phase column, Biofine RPC-SC 18 B, by gradient elution with 40–100% aqueous methanol. The derivatives were detected spectrofluorimetrically at 447 nm with excitation at 365 nm. The detection limits (signal to noise ratio = 3) for the acids were 3–6 fmol for an injection volume of 10 µl. The reagent was also applied to the derivatisation of some metabolites of arachidonic acid.
TL;DR: The inorganic ion exchanger chromium(III) hexacyanoferrate (III) has been found to be specifically selective for silver ions, with a sorption capacity of ca 10 mequiv g/1 of the exchanger as mentioned in this paper.
Abstract: The inorganic ion exchanger chromium(III) hexacyanoferrate(III) has been found to be specifically selective for silver ions, with a sorption capacity of ca 10 mequiv g–1 of the exchanger Sorption of the silver ions from acidic (10 mol dm–3 HNO3) and salt solutions (8 mol dm–3 NH4NO3), containing different levels of silver nitrate, has been studied The studies, which were aimed at using the exchanger for the recovery of silver ions from the waste, generated from chemical oxygen demand determinations, showed ca 80–95% recovery of silver ions from concentrated waste The exchanger also selectively removed silver ions from simulated waste containing Bi, Ca, Cd, Co, CuII, Mg, Mn, Ni, Pb and Zn ions
TL;DR: A review of the essential features and potential of (bio)chemical sensors, based on the immobilisation of the components of a chemical reaction (analyte, reagent, catalyst and products) in a flow cell placed in the light path of a molecular spectroscopic detector included in some of the continuous configurations based on flow-injection principles, is presented in this paper.
Abstract: A review of the essential features and potential of (bio)chemical sensors, based on the immobilisation of the components of a chemical reaction (analyte, reagent, catalyst and products) in a flow cell placed in the light path of a molecular spectroscopic detector included in some of the continuous configurations based on flow-injection principles, is presented. The kinetic implications of these new approaches in which reaction, and/or retention, is simultaneous with detection are also discussed.
TL;DR: A continuous-flow method based on the action of each corticosteroid as a sensitiser on the chemiluminescent oxidation of sulphite by cerium(IV) is described, which agreed well with those given by an official method.
Abstract: A continuous-flow method for the determination of cortisone, hydrocortisone, prednisolone and methylprednisolone in the range 0.100–1.00 µg ml–1 and of dexamethasone and betamethasone in the range 0.500–5.00 µg ml–1 is described. The procedure is based on the action of each corticosteroid as a sensitiser on the chemiluminescent oxidation of sulphite by cerium(IV). The analysis is automated, requires no sample pre-treatment and samples can be analysed at a rate of 40 per hour with a relative error of <6%. The method was evaluated by carrying out recovery experiments and by analysing commercial formulations. Results agreed well with those given by an official method.
TL;DR: Initial results are given here of a method that may approach this ideal for determining acylcarnitines in urine by chemical derivatisation, in which the zwitterionic acylCarnitine are cyclised to volatile lactones, and analysis by gas chromatography and gas Chromatography--mass spectrometry.
Abstract: Several inherited metabolic disorders, particularly the organic acidurias and acidemias, are often characterised by excretion of acylcarnitines, especially octanoylcarnitine, in the urine. Clinical investigation of such serious disorders ideally requires a rapid, simple and selective method for determining acylcarnitines in urine. Initial results are given here of a method that may approach this ideal. The procedure involves chemical derivatisation, in which the zwitterionic acylcarnitines are cyclised to volatile lactones, and analysis by gas chromatography and gas chromatography-mass spectrometry. Preparation of urine samples by ion-exchange purification and an illustrative application of the proposed method to a clinical sample are also outlined.
TL;DR: This survey of liquid chromatography and flow injection analysis reveals their common background and shared features, the various novel approaches possible and the lack of a unified theory.
Abstract: The purpose of this survey of liquid chromatography and flow injection analysis, which reveals their common background and shared features, the various novel approaches possible and the lack of a unified theory, is to highlight the compatibility of these techniques and to promote the interaction and exchange of ideas between areas of the newly emerging discipline of “injection techniques,” in the field of flow analysis.
TL;DR: In this paper, the authors investigated the effect of low concentrations of mineral acids on the emission intensity in inductively coupled plasma atomic emission spectrometry (PEAS) and found that the decrease in the excitation temperature and the reduction in the aspiration rate were two of the main factors responsible for lower emission intensities.
Abstract: Interferences caused by low concentrations of mineral acids have been investigated in inductively coupled plasma atomic emission spectrometry. There appear to be two mechanisms that lower the emission intensities: the decrease in the excitation temperature and the reduction in the aspiration rate. The former was predominant at lower concentrations of mineral acids (⩽1 M) and the latter became influential at higher acid concentrations (1 M). The excitation temperature was found to decrease in the presence of mineral acids. The decreases in emission intensities were in fair agreement with those estimated from the decreases in excitation temperature.
TL;DR: The spectral changes associated with the inclusion process allowed a value of 160 l mol-1 to be obtained for the complexation constant, and the method was applied satisfactorily to the determination of warfarin in irrigation water.
Abstract: The warfarin-β-cyclodextrin inclusion complex alters the luminescent properties of warfarin. This feature allows the use of a spectrofluorimetric method for its determination that gives improved analytical performance. The spectral changes associated with the inclusion process allowed a value of 160 l mol–1 to be obtained for the complexation constant. Fluorescence intensity is linearly related to warfarin concentration for a quantification limit of from 0.2 to 4 µg ml–1. The relative standard deviation at the 1.5 µg ml–1 level is 3.5%. The method was applied satisfactorily to the determination of warfarin in irrigation water.
TL;DR: Differential reaction-rate methods are a useful alternative to the sequential or simultaneous resolution of mixtures of closely related species without their prior separation as mentioned in this paper, which is one of the main objectives of modern analytical chemistry.
Abstract: Multi-component analysis is one of the main objectives of modern analytical chemistry. Differential reaction-rate methods are a useful alternative to the sequential or simultaneous resolution of mixtures of closely related species without their prior separation. The automatic and computerised instrumentation currently available, together with novel mathematical treatments and experimental methodologies, has turned these methods, formerly of purely theoretical interest, into practical tools for routine analyses.
TL;DR: A procedure for the indirect determination of L-tryptophan in serum has been developed, which is based on these findings, and enhances the selectivity of the voltammetric determination.
Abstract: The pre-concentration of indole and other indolic compounds of biochemical and pharmaceutical interest at a carbon paste electrode (Nujol/graphite) has been studied. All the compounds examined can be determined, by direct voltammetric measurements in their solutions, in the concentration range 1–8 µM. Indole, methylated indoles, harmaline and serotonin were accumulated at the electrode by a combined adsorption/extraction process. By applying the medium-exchange procedure, the accumulated compounds can be determined in the same concentration range, after a 60-s pre-concentration period, enhancing, therefore, the selectivity of the voltammetric determination. A procedure for the indirect determination of L-tryptophan in serum has been developed, which is based on these findings. L-Tryptophan was cleaved to indole by tryptophanase, and indole was subsequently determined voltammetrically after a 2-min pre-concentration period at the carbon paste electrode. From 0.3 to 1.2 µg of L-tryptophan in a total of 75 µl of serum sample (20–80 µM) can be determined with an average error of ca. 0.03 µg, whereas the recovery of added L-tryptophan in serum samples is in the range 105–115%.
TL;DR: Results were obtained, indicating the applicability of this technique for the determination of total airborne isocyanates, indicating that all tryptamine derivatised isOCyanates can be quantified using HPLC by employing a single, pure derivative, such as tryptamines derivatisation hexamethylene diisocyanate as the calibration standard.
Abstract: Determination of total airborne isocyanates using tryptamine as the derivatising agent was investigated. Tryptamine derivatised isocyanates were analysed by reversed-phase high-performance liquid chromatography (HPLC). The column was equipped with dual detectors of fluorescence emission and amperometric oxidation. The characteristics of fluorescence emission and amperometric oxidation of tryptamine were retained even after its reaction with isocyanates. With this unique behaviour, all tryptamine derivatised isocyanates can be quantified using HPLC by employing a single, pure derivative, such as tryptamine derivatised hexamethylene diisocyanate as the calibration standard. This is especially important for analysing polymeric isocyanates when identical calibration standards are not always available. The applicability of this method for air sampling was evaluated by comparison with the established method of Bagon et al. involving 1-(2-methoxyphenyl)piperazine. Simulation of air sampling was performed in a Test Atmosphere Generation System by the vaporisation of toluene diisocyanate. Satisfactory results were obtained, indicating the applicability of this technique for the determination of total airborne isocyanates.
TL;DR: In this article, trace metals in water were pre-concentrated on activated carbon after chelation with potassium ethyl xanthate, and the recoveries of Cd, Co, Cu, Hg and Zn at concentrations ranging from 10 to 500 ng ml-1, were >92, ≈85,>92, >93 and >92%, respectively.
Abstract: Trace metals in water were pre-concentrated on activated carbon after chelation with potassium ethyl xanthate. Optimum conditions for the maximum recovery of metal ions were developed. The recoveries of Cd, Co, Cu, Hg and Zn, at concentrations ranging from 10 to 500 ng ml–1, were >92, ≈85, >92, >93 and >92%, respectively. The method was used to determine these metals in water samples by instrumental neutron activation analysis and atomic absorption spectrometry.