Graphite-furnace atomic absorption spectrometry

The GFAAS technique, first developed in 1961 by L vov, was an attempt to improve the detection limits achievable. In this technique, instead of being sprayed as a fine mist into the flame, a measured portion of the sample is injected into an electrically heated graphite boat or tube, allowing a larger volume of sample to be handled. Eurthermore, by placing the sample on a small platform inside the furnace tube, atomisation is delayed until the surrounding gas within the tube has heated sufficiently to minimise vapour phase interferences, which would otherwise occur in a cooler gas atmosphere. 

The sample is heated to a temperature slightly above 100 C to remove free water, then to a temperature of several himdred degrees centigrade to remove water of fusion and 

Other volatiles. Finally, the sample is heated to a temperature near to 1000 C to atomise it and the signals produced are measured by the instrument. 

The problem of background absorption in this technique is solved by using a broad-band source, usually a deuterium arc or a hollow cathode lamp, to measure the background absorption independently and subsequently to subtract it from the combined atomic and background signal produced by the analyte hollow cathode lamp. By interspersing the modulation of the hollow cathode lamp and background corrector sources, the measurements are performed apparently simultaneously. 

Graphite furnace techniques are about one order of magnitude more sensitive than direct injection techniques. Thus lead can be determined down to 50 pg/1 by direct AAS and down to 5 pg/1 using the graphite furnace modification of the technique. 

The GFAAS technique, first developed in 1961 by L vov, was an attempt to improve the detection limits achievable. In this technique, instead of being sprayed as a fine mist 

The sample is heated to a temperature slightly above 100 °C to remove free water, then to a temperature of several hundred degrees centigrade to remove water of fusion and other volatiles. Finally, the sample is heated to a temperature near to 1000 °C to atomise it and the signals produced are measured by the instrument. 

Ritter and co-workers [1] conducted interlaboratory testing of polymers for the determination of cadmium, chromium and lead. They found that even when contaminant concentrations were identical the determination of heavy metals in plastics was strongly dependent on the polymer matrix. 

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Trace metals in sea water are preconcentrated either by coprecipitating with Ee(OH)3 and recovering by dissolving the precipitate or by ion exchange. The concentrations of several trace metals are determined by standard additions using graphite furnace atomic absorption spectrometry. 

L Vov, B. V. Graphite Furnace Atomic Absorption Spectrometry, AuflZ. Chem. 1991, 63, 924A-931A. 

Electrothermal vaporization can be used for 5-100 )iL sample solution volumes or for small amounts of some solids. A graphite furnace similar to those used for graphite-furnace atomic absorption spectrometry can be used to vaporize the sample. Other devices including boats, ribbons, rods, and filaments, also can be used. The chosen device is heated in a series of steps to temperatures as high as 3000 K to produce a dry vapor and an aerosol, which are transported into the center of the plasma. A transient signal is produced due to matrix and element-dependent volatilization, so the detection system must be capable of time resolution better than 0.25 s. Concentration detection limits are typically 1-2 orders of magnitude better than those obtained via nebulization. Mass detection limits are typically in the range of tens of pg to ng, with a precision of 10% to 15%. 

Figure 15-12 is a schematic illustration of a technique known as acid volatile sulfides/ simultaneously extracted metals analysis (AVS/SEM). Briefly, a strong acid is added to a sediment sample to release the sediment-associated sulfides, acid volatile sulfides, which are analyzed by a cold-acid purge-and-trap technique (e.g., Allen et ai, 1993). The assumption shown in Fig. 15-12 is that the sulfides are present in the sediments in the form of either FeS or MeS (a metal sulfide). In a parallel analysis, metals simultaneously released with the sulfides (the simultaneously extracted metals) are also quantified, for example, by graphite furnace atomic absorption spectrometry. Metals released during the acid attack are considered to be associated with the phases operationally defined as "exchangeable," "carbonate," "Fe and Mn oxides," "FeS," and "MeS."... 

Vol. 149. A Practical Guide to Graphite Furnace Atomic Absorption Spectrometry. By David J. Butcher and Joseph Sneddon... 

Nowka R, Muller H (1997) Direct analysis of solid samples by graphite furnace atomic absorption spectrometry with a transversely heated graphite atomizer and D2-background correction system (SS GF-AAS). Fresenius J Anal Chem 359 132-137. 

Hinds MW (1993) Determination of gold, palladium and platinum in high purity silver by different solid sampling graphite furnace atomic absorption spectrometry methods, Spectrochim Acta 48B 435-445. 

Klemm W, Baumeach G (1995) Trace element determination in contaminated sediments and soils by ultrasonic slurry sampling and Zeeman graphite furnace atomic absorption spectrometry. Fresenius J Anal Chem 353 12-15. 

LtiCKER E, Konig H, Gabriel G, Rosopulo A (1992) Analytical quality control by solid sampling graphite furnace atomic absorption spectrometry in the production of animal tissue reference materials. Fresenius J Anal Chem 342 941-949. 

Kelko-Levai, A., Varga, I., Zih-Perenyi, K., and Lasztity, A., Determination of trace elements in pharmaceutical substances by graphite furnace atomic absorption spectrometry and total reflection X-ray fluorescence after flow injection ion-exchange preconcentration, Spectrochim. Acta Pt. B, 54, 827, 1999. 

ZGFAAS Zeeman graphite furnace atomic absorption spectrometry... 

Aroza I, Bonilla M, Madrid Y, et al. 1989. Combination of hydride generation and graphite furnace atomic absorption spectrometry for the determination of lead in biological samples. J Anal Atmos Spectra 4 163-166. 

Ellen G, Van Loon JW. 1990. Determination of cadmium and lead in foods by graphite furnace atomic absorption spectrometry with Zeeman background correction Test with certified reference materials. Food Addit Contam 7 265-273. 

Zhang Z-W, Shimbo S, Ochi N, et al. 1997. Determination of lead and cadmium in food and blood by inductively coupled plasma mass spectrometry a comparison with graphite furnace atomic absorption spectrometry. Science of the Total Environment 205(2-3) 179-187. 

Zeeman Graphite Furnace Atomic Absorption Spectrometry... 

A limited amount of work has been carried out on the determination of molybdenum in seawater by AAS [107-109] and graphite furnace atomic absorption spectrometry [110]. In a recommended procedure a 50 ml sample at pH 2.5 is preconcentrated on a column of 0.5 gp-aminobenzylcellulose, then the column is left in contact with 1 mol/1 ammonium carbonate for 3 h, after which three 5 ml fractions are collected. Finally, molybdenum is determined by AAS at 312.2 nm with use of the hot-graphite-rod technique. At the 10 mg/1 level the standard deviation was 0.13 xg. 

Many of the published methods for the determination of metals in seawater are concerned with the determination of a single element. Single-element methods are discussed firstly in Sects. 5.2-5.73. However, much of the published work is concerned not only with the determination of a single element but with the determination of groups of elements (Sect. 5.74). This is particularly so in the case of techniques such as graphite furnace atomic absorption spectrometry, Zeeman background-corrected atomic absorption spectrometry, and inductively coupled plasma spectrometry. This also applies to other techniques, such as voltammetry, polarography, neutron activation analysis, X-ray fluroescence spectroscopy, and isotope dilution techniques. 

Bishop [75] determined barium in seawater by direct injection Zeeman-modulated graphite furnace atomic absorption spectrometry. The V203/Si modifier added to undiluted seawater samples promotes injection, sample drying, graphite tube life, and the elimination of most seawater components in a slow char at 1150-1200 °C. Atomisation is at 2600 °C. Detection is at 553.6 nm and calibration is by peak area. Sensitivity is 0.8 absorbance s/ng (Mo = 5.6 pg 0.0044 absorbance s) at an internal argon flow of 60 ml/min. The detection limit is 2.5 pg barium in a 25 ml sample or 0.5 pg using a 135 ml sample. Precision is 1.2% and accuracy is 23% for natural seawater (5.6-28 xg/l). The method works well in organic-rich seawater matrices and sediment porewaters. 

Epstein and Zander [76] used graphite furnace atomic absorption spectrometry for the direct determination of barium in seawater and estuarine... 

Dehairs et al. [78] describe a method for the routine determination ofbarium in seawater using graphite furnace atomic absorption spectrometry. Barium is separated from major cations by collection on a cation exchange column. The barium is removed from this resin with nitric acid. Recoveries are greater than 99%. 

Various workers have discussed the application of graphite furnace atomic absorption spectrometry to the determination of cadmium in seawater [ 115— 124],... 

Adsorptive cathodic stripping voltammetry has an advantage over graphite furnace atomic absorption spectrometry in that the metal preconcentration is performed in situ, hence reducing analysis time and risk of contamination. Additional advantages are low cost of instrumentation and maintenance, and the possibility to use adapted instrumentation for online and shipboard monitoring. 

A Cis column loaded with sodium diethyldithiocarbamate has been used to extract copper and cadmium from seawater. Detection limits for analysis by graphite furnace atomic absorption spectrometry were 0.024 pg/1 and 0.004 xg/l, respectively [283]. 

Hirao et al. [964] concentrated lead in seawater using a chloroform solution of dithizone and determined it in amounts down to 40 pg/1 by graphite furnace atomic absorption spectrometry. Lead in 1 kg acidified seawater was... 

Graphite-furnace atomic absorption spectrometry, although element-selective and highly sensitive, is currently unable to directly determine manganese at the lower end of their reported concentration ranges in open ocean waters. Techniques that have been successfully employed in recent environmental investigations have thus used a preliminary step to concentrate the analyte and separate it from the salt matrix prior to determination by atomic absorption spectrometry. 

Statham [448] has optimised a procedure based on chelation with ammonium dithiocarbamate and diethylammonium diethyldithiocarbamate for the preconcentration and separation of dissolved manganese from seawater prior to determination by graphite furnace atomic absorption spectrometry. Freon TF was chosen as solvent because it appears to be much less toxic than other commonly used chlorinated solvents, it is virtually odourless, has a very low solubility in seawater, gives a rapid and complete phase separation, and is readily purified. The concentrations of analyte in the back-extracts are determined by graphite furnace atomic absorption spectrometry. This procedure concentrates the trace metals in the seawater by a factor of 67.3. 

Graphite furnace atomic absorption spectrometry with the L vov platform and Zeeman background correction has been applied to the determination of down to 0.02 xg/l manganese in seawater [452]. 

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