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At least 145 records · Page 8Linked to original sources

PubMed1992

Improved high-performance liquid chromatographic procedure for the determination of lasalocid in chicken tissues and egg using polymeric and porous graphitic carbon columns.

A high-performance liquid chromatographic (HPLC) method for the determination of the ionophore coccidiostat lasalocid in poultry muscle and eggs was developed. The drug was extracted from tissue with acetonitrile. The extract was partitioned between saturated salt and carbon tetrachloride and the organic layer evaporated to dryness. Clean-up was by solid-phase extraction on a silica column. HPLC analysis was carried out on either a polymeric PLRP-S or a porous graphitic carbon Hypercarb column with a basic mobile phase and fluorescence detection with excitation at 310 nm and emission at 420-430 nm. Average recoveries from poultry muscle at the 0.002, 0.010 and 0.050 mg kg-1 levels were 65.7, 72.0 and 77.9%, respectively. Average recoveries from egg at the 0.010 and 0.100 mg kg-1 levels were 76.2 and 76.4%, respectively.

Animals↗

PubMed1995

Graphite surface-assisted laser desorption/ionization time-of-flight mass spectrometry of peptides and proteins from liquid solutions.

Laser desorption time-of-flight mass spectra of peptides and proteins, as well as of lower molecular weight analytes, have been obtained by using a pulsed nitrogen UV laser (337 nm) to irradiate mixtures of 2-150 microns graphite particles and solutions of the analytes in glycerol. Protonated analytes as well as abundant alkali cation adducts were observed. Carbon cluster ions, Cn+, typically had a low abundance but dominated the mass spectrum at elevated laser powers. In spectra of a cytochrome c tryptic digest, all but one of the tryptic peptides were easily observed. Spectra of low molecular weight analytes dissolved in glycerol are very similar to FAB spectra of the same glycerol solution with added alkali salts. However, in many peptide and protein spectra, glycerol ion abundances are very low, and the alkali ions dominate the spectra at low mass. These spectra may correspond to wet and dry surface desorption conditions, respectively. The best spectra of the larger molecules were observed under dry conditions. In these initial experiments, we have obtained a sensitivity in the pico- to nanomole range and a mass resolution of about 300. The signal intensity is as good as that in conventional MALDI, and under optimal conditions, few background peaks appear, even at low mass.

Mass Spectrometry↗

PubMed1989

Continuum source atomic absorption spectrometry in a graphite furnace with photodiode array detection.

A graphite furnace continuum source atomic absorption spectrometer using a photodiode array detector is described that provides high-resolution wavelength versus absorbance spectra over a 2.5-nm range for a single atomization step. The multiwavelength detection power allows the simultaneous determination of several elements, reduces problems caused by spectral interferences, and automatically corrects for nonzero background absorbance. Each spectrum is acquired in 0.33 s, and several successive spectra can be obtained during a single run. Three-dimensional wavelength-absorbance-furnace temperature spectra can be obtained by using ramped heating steps to provide a rough separation of elements in a mixture. Limits of detection calculated for 19 elements range from 0.1 pg for magnesium to 700 pg for arsenic. The sampling precision was found to be better than 10% relative standard deviation in all cases, with the precision for a single atomization being greatly increased when multiple absorption lines for a single element are observed in the spectrum. The error found for the measurement of the iron concentration in an NBS standard bronze was 8.5%, with the calculated concentration agreeing with the certified concentration within 95% confidence limits.

Metals↗

PubMed1989

Direct determination of iron in urine and serum using graphite furnace atomic absorption spectrometry.

A simple, rapid and low-cost method for the routine determination of iron in urine and serum using graphite furnace atomic absorption spectrometry is described which may provide an alternative to the more widespread automated spectrophotometric methods. The urine and serum samples were simply diluted with water prior to analysis. Matrix modification was found to be redundant. The standard additions technique or the use of matrix matched standards (addition calibration) was found to be unnecessary and, therefore, the calibration was performed using aqueous standards. For serum analysis the degree of dilution could be reduced by using the less sensitive 302.0-nm resonance line, yielding more precise determinations, and for urine analysis, interferences were eliminated by means of a L'vov platform. The interferences that exist in the presence of nitric acid are also discussed. Finally, the presence of background absorption was investigated by means of Zeeman effect atomic absorption.

Humans↗

PubMed1989

Direct determination of cadmium in urine using graphite furnace atomic absorption spectrometry with Zeeman-effect background correction.

A procedure is described for the direct determination of cadmium in human urine using graphite furnace atomic absorption spectrometry with Zeeman-effect background correction. Except for a straightforward 1 + 1 V/V dilution of samples with 1.5% nitric acid, no matrix modifier or sample pre-treatment was necessary, thus reducing the risk of contamination. The concentration of cadmium in urine was evaluated directly from a calibration graph prepared using a metal-spiked human urine pool. In this way the time-consuming method of standard additions was avoided, permitting an increased sample throughput (120-150 samples per day; 90 s per analysis) with minimal attention of the analyst. In routine use, the precision (both within day and day to day) and limit of detection were of the order of less than 10% and 0.05 micrograms l-1 of Cd, respectively. The method is suitable for the biological monitoring of cadmium in the general population or in occupationally exposed persons.

Cadmium↗

PubMed1989

Determination of molybdenum in plasma using graphite furnace atomic absorption spectrometry.

A sensitive method is described for the determination of Mo in plasma or serum by graphite furnace atomic absorption spectrometry. The method involves extraction of the metal as the 8-hydroxyquinoline complex and is free of the interference effects that prevent the direct analysis of plasma for Mo. Recoveries of internal standards were excellent and results from the analysis of a National Institute of Standards and Technology Standard Reference Material were in good agreement with certified values. The sensitivity of the method, based on the analysis of 1 ml of plasma, is ca. 3 ng ml-1.

Animals↗

PubMed1990

Evaluation of biological sample mineralisation methods for the determination of fluorine by graphite furnace molecular absorption spectrometry.

Various mineralisation methods were evaluated as means of treating different liquid and solid biological samples for the determination of fluorine by the formation of aluminium monofluoride in an electrothermal graphite furnace and molecular absorption spectrometry (AIF-MAS). Simple sample dilution and the use of 0.01 M Al3+ + 0.01 M Sr2+ solution as a matrix modifier are sufficient to determine the fluorine content in most liquid samples, although some require the addition of 0.3 M ammonium nitrate to the matrix modifier solution in order to diminish background absorbance. In solid samples, treatment methods routinely used with fluoride ion-selective electrodes such as microdiffusion, furnace ashing - microdiffusion and oxygen flask combustion, were tested for compatibility with AIF-MAS. The results were compared with those obtained with a fluoride ion-selective electrode. The proposed mineralisation methods were checked for applicability to different plants, foodstuffs and other biological materials. Some of the methods gave an over-all precision of better than 10%, which is often acceptable, and all methods gave recoveries above 80%. Differences between labile + ionic fluoride and total fluorine can be established by sample treatment.

Evaluation Studies as Topic↗

PubMed1990

Determination of trace amount of cobalt in feed grains and forages by solvent extraction and graphite furnace atomic absorption spectrometry.

A method is described for the determination of trace amounts of cobalt in feed grains and forages with a detection limit of 1 ng g-1. Samples are ashed in a muffle furnace and complexed with 2-nitroso-1-naphthol. Following solvent extraction, cobalt is determined using graphite furnace atomic absorption spectrometry. The assay can be carried out in a normal analytical laboratory without the need for special "clean" rooms. Reagents have been selected to keep reagent blank values at low levels, and heptan-2-one is used as extracting solvent to avoid problems with evaporation. The assay has been used for diagnostic purposes and to formulate special low cobalt diets for sheep for experimental purposes.

Animal Feed↗

PubMed1993

Electrocatalytic reduction of hydrogen peroxide at a stationary pyrolytic graphite electrode surface in the presence of cytochrome c peroxidase: a description based on a microelectrode array model for adsorbed enzyme molecules.

Electrochemical reduction of H2O2 at pyrolytic graphite disc electrodes of radius 2.5 mm occurs at readily accessible potentials (600 mV versus the standard hydrogen electrode) in the presence of yeast cytochrome c peroxidase. Introduction of the enzyme into the electrolyte solution initiates large changes in the ellipsometric angles measured for the electrode-solution interface, consistent with time-dependent enzyme adsorption. This process may be correlated with changes in electrochemical activity. Over the same time course, linear-sweep voltammograms are characterized by a transition from a sigmoidal to a peak-type waveform. It is proposed that the time-dependent behaviour may be rationalized by use of a microscopic model for substrate mass transport, in which the two-electron reduction of peroxide occurs at electrocatalytic sites consisting of adsorbed enzyme molecules. A voltammetric theory based on treating the adsorbed redox enzymes as an expanding array of microelectrodes is in excellent agreement with experiment.

Adsorption↗

PubMedDate not supplied

Determination of cadmium and lead in foods by graphite furnace atomic absorption spectrometry with Zeeman background correction: test with certified reference materials.

Two methods for the determination of cadmium and lead based on graphite furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction are described. The main difference between the methods is the method of sample destruction, bomb digestion versus dry ashing. The precision and accuracy of the methods has been tested by analysing 16 different reference materials, with cadmium concentrations varying from 2.9 micrograms/kg to 2.7 mg/kg and lead concentrations from 44 micrograms/kg to 13.5 mg/kg. The methods produced results which differ, with a few exceptions, less than 10% from the certified contents, with relative standard deviations of around 5%. The methods are not difficult to carry out, are not very laborious and without modifications are applicable to a large variety of products. The sample solutions obtained can also be used for the determination of other elements, e.g. Al, Cr, Cu, Hg, Mn, Ni and Zn. The detection limits, for test portions of 1 and 5 g (wet products) are 0.5-1 microgram/kg for cadmium and 5-20 micrograms/kg for lead.

Animals↗

PubMed1980

Determination of total tin in environmental biological and water samples by atomic absorption spectrometry with graphite furnace.

Analysis of traces of tin using several analytical techniques (X-ray fluorescence, neutron activation, polarographic techniques and atomic absorption) have been tested. Parameters such as simplicity, rapidity, sensitivity and interferences are compared in order to choose the most useful method for practical purpose. Finally, flameless atomic absorption was chosen for the determination of total tin concentration in different natural samples. Digestion of biological samples (plant, plankton, fish, etc.) was achieved by using Lumatom (a trade organic chemical). Thus, the digested sample is directly injected into the graphite furnace. This digestion technique is suitable and rapid with a minimum of error (contamination and losses). For tin analysis in water samples, a preconcentration of tin is carried out by coprecipitation with 1, 10-phenanthroline and tetraphenyl boron. The precipitate is separated and dissolved in alcohol or in Lumatom. The sensitivity of this method is 0.1 ng absolute tin.

Animals↗

PubMed1986

Determination of ultra trace amounts of cobalt in fish by graphite furnace Zeeman effect atomic absorption spectrometry.

A method is described for determining stable cobalt concentrations in fish flesh and bone using polarized Zeeman effect graphite furnace atomic absorption spectrometry (ZAAS). Cobalt analysis on freshwater fish flesh samples (10 g dry weight) required predigestion and wet-ashing at 70-80 degrees C. Cobalt is chelated with ammonium pyrrolidine dithiocarbamate (APDC) extracted with methyl isobutyl ketone (MIBK) and analysed by ZAAS. The mean cobalt content calculated from the standard additions method using three replicate fish flesh samples was 4.23 +/- 1.0 microgram Co. Kg-1 (dry weight). Analyses were also carried out on flesh and bone samples from similar sized fish, of the same species, taken from three area lakes.

Animals↗

PubMed1991

Graphitized carbon black in quartz tubes for the sampling of indoor air nicotine and analysis by microwave thermal desorption-capillary gas chromatography.

Nicotine in a smoky indoor air environment can be determined using graphitized carbon black as a solid sorbent in quartz tubes. The temperature stability, high purity, and heat absorption characteristics of the sorbent, as well as the permeability of the quartz tubes to microwaves, enable the thermal desorption by means of microwaves after active sampling. Permeation and dynamic dilution procedures for the generation of nicotine in the vapor phase at low and high concentrations are used to evaluate the performances of the sampler. Tube preparation is described and the microwave desorption temperature is measured. Breakthrough volume is determined to allow sampling at 0.1-1 L/min for definite periods of time. The procedure is tested for the determination of gas and paticulate phase nicotine in sidestream smoke produced in an experimental chamber.

Air Pollutants↗

PubMedDate not supplied

Determination of tin in biological materials by atomic-absorption spectrometry with a graphite furnace.

The determination of tin in the blood, liver, kidney, and spleen by atomic-absorption measurement using a graphite furnace was investigated. The presence of 20 micrograms/mL Fe(III) reduced absorbance of 0.2 microgram/mL Sn to 50%. To remove the interference of Fe(III), it was reduced to Fe(II) by 10% ascorbic acid, and Sn(IV) was extracted by methylisobutylketone (MIBK) without a chelating agent. This technique can be applied when 100 micrograms/mL Fe coexists with 0.2 microgram/mL Sn. Four methods for determination of tin in the blood were examined: (a) standard addition, (b) low-temperature ashing/MIBK extraction, (c) wet ashing/MIBK extraction, and (d) direct determination. The results of (a), (b), and (c) showed a high correlation (r greater than 0.86, n = 12), while the values obtained by (d) were scattered widely and showed little correlation with those determined by the other three methods. In methods (b) and (c), the detection limit was 10 ng/mL (0.2 ng Sn) without expansion mode, 2 ng/mL (0.04 ng Sn) with X 5 expansion mode, the recovery more than 90%, and the coefficient of variation 6.6% (n = 8). Method (c) was recommended for large sample sizes, and was also suitable for determination of tin in liver, kidney, and spleen, using 0.5%, instead of 10%, ascorbic acid.

Animals↗

PubMedDate not supplied

Axial distribution of arsenic in individual human hairs by solid sampling graphite furnace AAS.

In cases of arsenic poisoning, the distribution of arsenic along the length of a hair can be used to distinguish between chronic and acute exposure. Individual 5-mm segments of a hair were analyzed for their arsenic content by solid sampling graphite furnace atomic absorption spectrophotometry with a mixed Pd-Mg(NO3)2 matrix modifier. Results obtained using arsenic calibration solutions and standard additions to uncontaminated hairs are analytically indistinguishable, allowing aqueous standards to be used for hair analysis. The characteristic mass is 24 pg, and the 3 sigma detection limit is approximately 10 pg. Results obtained for hairs from two victims of arsenic poisoning are in good agreement with those obtained using neutron activation analysis.

Arsenic↗

PubMed1983

Microanalysis of platinum in biological media by graphite furnace atomic absorption spectroscopy.

An accurate method for the analysis of platinum in biological matrix is described. The method requires minimal sample handling and pretreatment prior to injection into the graphite furnace. It is reproducible, with average recovery of 97.7% platinum in biological matrix. The data presented also demonstrate that Fe in particular (also NaCl and HNO3) significantly depresses the atomic absorption signal of platinum. Standard addition calibration curves are therefore essential for determination of platinum in biological samples.

Humans↗

PubMedDate not supplied

Graphite calorimeter in water phantom and calibration of ionization chambers in dose to water for 60Co gamma radiation.

A graphite calorimeter similar in size and shape to a Farmer type 0.6-cm3 ionization chamber was developed for direct measurement of absorbed dose at a specified depth in a water phantom irradiated by a beam of 60Co gamma radiation. The accuracy of the absorbed dose determined was estimated to be +/- 1.1% at a dose level of 4 rad/s (4 X 10(-2)Gys-1). The absorbed dose to water at the calibration depth of 5 cm was standardized for our 60Co gamma bean, for a 60-cm SSD and 10 X 10 cm2 field. Farmer type ionization chambers were calibrated against the standardized absorbed dose. The overall accuracy in calibrating the ionization chambers was +/- 1.2%.

Calibration↗

PubMed1995

Lead and cadmium in human placentas and maternal and neonatal blood (in a heavily polluted area) measured by graphite furnace atomic absorption spectrometry.

OBJECTIVE: To measure the concentrations of the trace elements lead and cadmium in human placenta and in maternal and neonatal (cord) blood. To assess the influence of the strongly polluted environment on the content of metals in tissues and on the permeability of placenta to cadmium and lead. Various methods of mineralisation were tested before analysis. METHODS: Graphite furnace atomic absorption spectrometry was used for the determination of lead and cadmium. The samples for analysis were prepared by mineralisation under pressure in a Teflon bomb (HNO3, 110 degrees C), by wet ashing under normal pressure (HNO3 + H2O2 for 12 hours), and by microwave digestion in concentrated nitric acid. RESULTS: In analysed samples the following mean concentrations of cadmium and lead were found: in venous blood Pb = 72.50 ng/ml, Cd = 4.90 ng/ml; in placenta Pb = 0.50 microgram/g, Cd = 0.11 microgram/g; in cord blood Pb = 38.31 ng/ml, Cd = 1.13 ng/ml. CONCLUSION: High concentrations of lead and cadmium were found in placentas and in maternal blood whereas in neonatal blood there was an increased concentration of lead and only traces of cadmium. It is concluded that the placenta is a better barrier for cadmium than for lead. Among the examined methods of mineralisation, microwave digestion was the best.

Cadmium↗