Determination of chromium in human milk and urine by graphite-furnace atomic absorption spectrometry

Low-temperature ashing and dry ashing at 500°C are compared for the analysis of urine and human milk. Dry ashing gives superior accuracy. The importance of contamination control, background correction and temperature control are stressed. Both urine and human milk contain about 1 ng Cr ml^-1.     

Determination of beryllium and selenium in human urine and of selenium in human serum by graphite-furnace atomic absorption spectrophotometry.

For human urine beryllium (Be), each sample (500 microl) was diluted (1+1) with Nash reagent (containing 0.2% (v/v) acetylacetone and 2.0 M ammonium acetate buffer at pH 6.0) and then a 20-microl volume of Triton X-100 (0.4%, v/v) aqueous solution was added. An aliquot (10 microl) of the diluted urine mixture was introduced into a graphite cuvette and was atomized according to a temperature program. The method detection limit (MDL, 3sigma) for Be was 0.37 microg/l in the undiluted urine sample and the calibration graph was linear up to 65.0 microg/l. Calibration graphs were prepared by the standard addition method. Accuracies of 98.6-102% were obtained when testing standard reference material (SRM 2670) freeze dried human urine samples. Precision (relative standard deviation, RSD) for urine Be was < or = 2.3% (withinrun, n = 5) and was < or = 3.0% (between-run, n = 3). For human urine and serum selenium (Se), samples (100 microl) were diluted with HNO3 (0.2%, v/v) to make a (1+1) dilution for urine analysis or a (1+4) dilution for serum analysis. An additional aliquot (10 microl) of Triton X-100 (0.1%, v/v) was added to each 200 microl of (1+1) diluted urine (or 20 microl of the Triton X-100 was added to each 500 microl of (1+4) diluted serum) sample. After the diluted sample mixture (10 microl) was introduced into a graphite cuvette, the corresponding chemical modifier (10 microl, containing Ni2+ + Pd + NH4NO3 in HNO3 (0.2%, v/v)) was added to it and the mixture was atomized. The MDL (3sigma) for Se in urine and in serum was 4.4 and 21.4 microg/l in undiluted sample, respectively, and the calibration graphs were linear up to 150 and 400 microg/l. Accuracies of urine Se were 98.9 - 99.4% by testing SRM 2670 (NIST) urine standards with RSD (between-run, n = 3) within 2.9%; and that of serum Se was 97.2% when testing a certified second-generation human serum (No. 29, #664) with RSD (between-run, n = 3) of 1.4%. The proposed method can be applied easily, directly, and accurately to the measurement of Be and Se in real samples (including six urine Se and four serum Se from patients of Blackfoot Disease in Taiwan).     

Determination of trace metals in estuarine sediments by graphite-furnace atomic absorption spectrometry

A simple and rapid acid digestion method for the decomposition of estuarine sediments is described. Quantitative recovery of Cd, Pb, Cu, Ni, Co, Be and Co is demonstrated. Sensitive, precise and accurate determination of these trace metals by graphite-furnace atomic absorption spectrometry in combination with the L'vov Platform provides an interference-free technique that permits calibration with simple aqueous solutions of metal standards. The accuracy of the method has been confirmed by analysis of two marine sediment reference materials, MESS-1 and BCSS-1.     

Silica gel analysis by slurry-sampling graphite-furnace atomic absorption spectrometry

Analytical conditions for the determination of cadmium, lead, copper, iron, aluminium and titanium in commercial silica gel samples by slurry-sampling graphite-furnace atomic absorption spectrometry are established. The influence of the silica matrix on the background absorption is described. Stability tests for slurries have been carried out. Results are calculated by the method of standard additions. Statistical evaluations of the results indicate that the slurry method is reproducible and its precision is comparable to other methods used. Advantages of this method are simplicity and short time of analysis.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992; Geel, Belgium. Papers edited by R.F.M. Herber, Amsterdam     

Determination of vanadium in urine by electrothermal atomic absorption spectrometry

After wet ashing of the urine sample with nitric acid, vanadium is chelated with cupferron, extracted into 4-methylpentan-2-one and determined by atomic absorption spectrometry with a pyrolytically-coated graphite furnace atomizer. The sensitivity allows the precise determination of 1–500 μg V l^-1 in urine. The coefficient of variation for triplicate urine measurements is <8% for 10 μg V l^-1.     

Semi-permanent lutetium modifier for the determination of beryllium in urine by electrothermal atomic absorption spectrometry

The determination of beryllium using electrothermal atomic absorption spectrometry with deuterium background correction in the presence of various isomorphous metals and Mg(NO₃)₂ was studied. While, Eu, Ir and Sm had no effect on the transient signals, the addition of Lu and Mg(NO₃)₂ improved the sensitivity of the beryllium signal with respect to that obtained in the absence of modifier. Although, Mg(NO₃)₂ has improved the signal with respect to its sensitivity, it also increased the tail and the background (BG) signals, specially when urine samples are under study. Whereas, when Lu was used the analytical signal is virtually free of BG interference indicating that the urine matrix interference was almost eliminated. Besides, the addition of 6 μg of Lu ensured that the signals were effectively constant for five firings following the furnace program, which included: three drying, and the pyrolysis, atomization, cleaning and cooling steps. The effect of some components, likely to interfere in the accurate determination of beryllium (such as: Al, Ca, Cl, Co, Cr, Fe, Mg and Mn) were investigated. At the physiological levels, most of these elements had no effect, except in the case of chloride when Mg(NO₃)₂ was used as modifier. In this case, the tolerance limit was of 3000 mg Cl⁻ l⁻¹. The characteristic masses were 1.19, 0.45 and 0.48 pg, when integrated absorbance was measured for beryllium without the addition of any modifier and in the presence of Lu and Mg(NO₃)₂, respectively. The limits of detection (3σ) were 85, 19 and 58 fg, respectively. The accuracy and precision with the use of Lu and Mg(NO₃)₂ was tested for the direct determination of beryllium in urine samples. Quantification was performed with aqueous standards. The results obtained for the determination of beryllium in reference materials (Trace Elements in Urine), together with good recovery of spiked analyte, using either Lu or Mg(NO₃)₂ modification demonstrate the applicability of the procedure to the analysis of real samples. However, Lu provided the most accurate results. Also, the addition of Lu enhanced the precision of the measurements to levels of 1.8% relative standard deviation instead of 5.6 and 3.3% for the case of beryllium alone and with the addition of Mg(NO₃)₂.     

A study of background signals in graphite-furnace atomic absorption spectrometry

The non-specific absorption from inorganic and organic molecules between 190 and 400 nm are measured using a graphite furnace and an atomic absorption spectrometer with a deuterium source.The molecular absorption spectra of NaCl, KCl, RbCl and CsCl are very similar, with two maxima at ca. 200 and 250 nm. That of LiCl is very weak, as is that of NaF. The spectra of NaBr, NaI, KBr, KI, CaCl₂, MgCl₂, SrCl₂, FeCl₃, LaCl₃ are also reported.The non-specific absorption spectrum arising from albumin decreases fro 190 to 400 nm, and that for plasma is similar to albumin, although a contribution from inorganic salts can also be seen. To decrease the non-specific absorption from metal chlorides or biological samples of mainly inorganic composition such as urine, addition of HNO₃ is satisfactory. Oxygen introduction during low temperature charring is better for removing contribution from organic molecules.     

Determination of trace elements in gallium arsenide by graphite-furnace atomic absorption spectrometry after pretreatment in gas streams

Atomic absorption spectrometry (AAS) with a resistively-heated graphite furnace is used for the determination of chromium (0.3–1 atom/10⁶ atom) in chromium-doped gallium arsenide after pretreatment in a separate furnace in a stream of argon to remove arsenic, and of manganese and silver (0.03 and 0.04 atom/10⁶ atoms, respectively) by a similar procedure after pretreatment with argon and chlorine, the latter to remove both gallium and arsenic as volatile chlorides. Results for chromium were in agreement with those obtained by furnace AAS after dissolution and by spark-source mass spectrometry (SSMS) but AAS after dissolution is more precise. Results for manganese and silver obtained by both gas pretreatments were in good agreement, but were higher than those obtained for presparked material by SSMS, indicating that surface contamination of gallium arsenide was not completely removed by the etching methods used. The procedures established that the concentrations of bismuth, indium and lead in the gallium arsenide sample were below the limits of detection of 3 × 10^?3, 10 × 10^?3 and 1 × 10^?3 atom/10⁶ atoms, respectively. In all cases, calibration graphs were constructed from data obtained with aqueous solutions of appropriate salts.     

Determination of arsenic in urine by atomic absorption spectrometry with electrothermal atomization

A cheap device which can be used to follow transient signals with a chart recorder is described.     

Determination of manganese in serum and urine by electrothermal atomic absorption spectrometry

Manganese is determined in serum and urine by graphite-furnace atomic absorption spectrometry after dilution (1 + 1) with distilled water. Simple aqueous standards are used for calibration. Background absorption from the matrix is decreased by attention to the heating programme, sample dilution and gas flow-rate during atomisation. Remaining background absorption is removed by a deuterium-arc background correction system. To obtain accurate results, great care is needed in collecting samples to avoid contamination. Blood is collected through a plastic cannula, because stainless steel needles introduce considerable contamination. The mean normal concentration of manganese in serum was found to be 0.58 μg l^?1 (it- = 9) which is in agreement with other literature values. For urine, the mean normal concentration found was 0.7 μg l^?1 (it- = 16). Patients on total parenteral nutrition with manganese supplements show elevated serum and urine manganese concentrations.     

Determination of trace elements in sea water by graphite-furnace atomic absorption spectrometry after preconcentration by tetrahydroborate reductive precipitation

A method is described for the preconcentration of 16 elements from coastal and deep ocean sea water based on their reductive precipitation by sodium tetrahydroborate. The enrichment factors obtained were sufficient to permit the analysis of a near-shore sea-water reference material (11 elements) and an open ocean sea-water reference material (9 elements). Recoveries from 900 ml of sea water ranged from 80 to 107% (100-ml sample for Mn) with absolute blanks between <1.0 ng (Se) and 20 ng (Cu). Estimated detection limits varied from 0.3 ng l ^?1 (Pb) to 19 ng l^?1 (As) based on a 36-fold concentration of a 900-ml sample.     

Determination of cobalt and nickel by graphite-furnace atomic absorption spectrometry after coprecipitation with scandium hydroxide.

Trace amounts of cobalt and nickel in a water sample were quantitatively coprecipitated with scandium hydroxide at pH 8.0-10.5. Because the coprecipitant could be easily dissolved with 1 mol dm(-3) nitric acid, and the presence of up to 10 mg cm(-1) of scandium did not interfere with the graphite-furnace atomic absorption spectrometric determination of cobalt and nickel, the volume of the final solution prepared for the determination could be minimized down to 0.5 cm3. The concentration factor was 400-fold and the detection limits (signal to noise = 2) were 5.0 pg cm(-3) of cobalt and 10.0 pg cm(-3) of nickel in 200 cm3 of the initial sample solution. The 27 diverse ions investigated did not interfere with the determination in at least a 500-fold mass ratio to cobalt or nickel. The proposed method was successfully applied to the determination of trace amounts of cobalt and nickel in river-water samples.     

Determination of mercury in biological tissues by graphite-furnace atomic absorption spectrometry with an in-situ concentration technique.

A method has been described for the determination of total mercury by graphite-furnace atomic absorption spectrometry (GFAAS) using an in-situ concentration technique with a Pd-Zr coating and a chemical modifier. The characteristic mass, which gives an integrated absorbance of 0.0044 s, was found to be 42 pg and an absolute detection limit (3sigma) of 33 pg was obtained with the proposed modifier. The total mercury values in standard reference materials, including Mussel (GBW08571), Bovine liver (GBW08306), Peach leaf (GBW08501) and Tea leaf (GBW080001), were determined using the proposed method, and the results were consistent with reference values. The method had been successfully applied to the determination of mercury in biological tissue samples with a recovery range of 94-105%.     

Determination of silver in sea water by coprecipitation with cobalt pyrrolidinedithiocarbamate and Zeeman graphite-furnace atomic absorption spectrometry

A preconcentration technique is described for silver, which allows the precise and accurate determination of silver in sea water at nanogram per liter levels. Silver is co-precipitated with cobalt(II) pyrrolidinedithiocarbamate from 200-ml samples. The precipitate is dissolved in concentrated nitric acid and silver is quantified by Zeeman graphite-furnace atomic absorption spectrometry, with acid phosphate matrix modification. The detection limit is 0.1 ng l^?. The method is simple and rapid, and also allows the simultaneous extraction of lead, copper, cadmium, and nickel.     

Determination of cadmium in spring water by graphite-furnace atomic absorption spectrometry after coprecipitation with ytterbium hydroxide.

A coprecipitation method with ytterbium hydroxide was studied for the determination of cadmium in water samples by graphite-furnace atomic absorption spectrometry. Up to 40 ng of cadmium in water samples was quantitatively coprecipitated with ytterbium hydroxide at pH 8.0-11.2. The concentration factor was 100 fold. The coprecipitated cadmium was sensitively determined without any influence of ytterbium and the calibration curve was linear from 0.1 to 4 ng/mL of cadmium. The detection limit (signal/noise = 2) was 2.9 pg/mL in 100 mL of the initial sample solution. Twenty-nine diverse ions tested did not interfere with the determination in at least a 10000-fold mass ratio to cadmium. The proposed method was successfully applied to the determination of cadmium in spring water.     

Determination of beryllium by electrothermal atomic absorption spectrometry using tungsten surfaces and zirconium modifier

Electrothermal atomization of beryllium from graphite and tungsten surfaces was compared with and without the use of various chemical modifiers. Tungsten proved to be the best substrate, giving the more sensitive integrated atomic absorption signals of beryllium. Tungsten platform atomization with zirconium as a chemical modifier was used for the determination of beryllium in several NIST SRM certified reference samples, with good agreement obtained between the results found and the certified values. The precision of the measurements (at 10 μg L⁻¹), the limit of detection (3σ), and the characteristic mass of beryllium were 2.50%, 0.009 μg L⁻¹ and 0.42 pg, respectively.     

Determination of inorganic tin and organotin compounds by graphite-furnace atomic absorption spectrometry with a new matrix modifier

The determination of total tin in water samples by graphite-furnace atomic absorption spectrometry is described. A matrix modifier containing 0.4% (w/v) potassium dichromate and 0.2% ammonium dihydrogenphosphate in 2% nitric acid is proposed. Interferences from major ions in natural fresh waters decreased and the sensitivity is greatly improved. The procedure is compatible with all the commercial injection devices and requires no pretreatment of the graphite furnace or use of a stabilized temperature platform. The 3σ detection limit is 0.62 ng Sn ml^?1, and calibration is linear up to 30 ng ml^?1 tin.     

Determination of lead and cadmium in urine by electrothermal atomization atomic absorption spectrometry

The applicability of a DETATA sorbent to the preconcentration of lead and cadmium followed by the determination of these elements in urine using atomic absorption spectrometry with electrothermal atomization was demonstrated. After preconcentration by a factor of 10, the limits of detection were 0.01 and 0.2 μg/L for cadmium and lead, respectively. The accuracy of the results was supported by the analysis of Seronorm Trace Elements Urine (Batch no. 101021).     

Comparison of carrier elements for coprecipitation and graphite-furnace atomic absorption spectrometry

The group IIIB elements (aluminum, gallium and indium) and iron(III) were studied from the standpoint of the advantageous combination of coprecipitation and graphite-furnace atomic absorption Spectrometry (GFAAS). Milligram quantities of four hydroxides were precipitated at different pH's from solutions containing traces of copper(II) and cadmium(II) ions, in order to examine the effect of pH on the coprecipitation. Almost similar results were obtained for gallium, indium and iron hydroxides, with which the copper and cadmium were coprecipitated nearly completely at pH>7. In case of aluminum hydroxide, the optimal pH range was narrow because of the redissolution of the precipitate in alkaline solutions. The removal of indium carrier was successfully achieved by volatilization as bromide at the pyrolysis stage in GFAAS, otherwise serious background absorption interfered with the trace determination. Volatilization loss of cadmium was eliminated by adding a small amount of miourea. Gallium carrier was mostly removed as chloride, but large background absorption still occurred in the determination of cadmium.