GFAAS

The GFAAS technique was first developed in 1961 by Cvov. It was an attempt to improve detection limits. 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. 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 hundred degrees centigrade to remove water of fusion and other volatiles. The sample is heated to a temperature near 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 broadband source, usually a deuterium arc or a hollow cathode lamp, to measure the background 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, measurements are done apparently simultaneously. 

Graphite furnace techniques are about one order of magnitude more sensitive than direct injection techniques. Lead can therefore be determined down to 50 pg/1 using the graphite furnace modification of the technique. 

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ICP-OES is a destructive technique that provides only elemental composition. However, ICP-OES is relatively insensitive to sample matrix interference effects. Interference effects in ICP-OES are generally less severe than in GFAA, FAA, or ICPMS. Matrix effects are less severe when using the combination of laser ablation and ICP-OES than when a laser microprobe is used for both ablation and excitation. 

Althoi h nonspectral interference effects are generally less severe in ICP-OES than in GFAA, FAA, or ICPMS, they can occur. In most cases the effects produce less than a 20% error when the sample is introduced as a liquid aerosol. High concentrations (500 ppm or greater) of elements that are highly ionized in the... 

In order to derive a quantitative relation between emission Intensity as measured by EMI and actual metal content, cell samples were subjected to graphite furnace atomic absorption (GFAA) analysis (14). Atomic absorption experiments were performed both on cells which had been stained with a fluorescent reagent and on cells not exposed to a lumlnophore. After EMI analysis, 50 fiL of cell suspension were withdrawn from the 0.30 mL of sample used for EMI and were digested In 150 iiL of concentrated HNO3 for 90 minutes at 85° . These solutions were then diluted to 1/10 of their concentration with deionized water, and the 150 liL of these diluted... 

Cell suspensions which were exposed to 1.0 ppm zinc were combined, and to this matrix known amounts of Zn were added, to allow measurement of the amount of zinc accumulated by the cells via GFAA. In related work, cells treated with known concentrations of zinc solutions were systematically combined and thereby "diluted" with cells not exposed to zinc, to determine If GFAA and EMI analyses yield confirmatory results. 

Pseudomonas 244 cells were exposed to Bu Sn (x = 0,1,2,3) to compare the relative affinities the cells had for the differing species. The cells were exposed to 10 ppm solutions of the various tin species for over 2h hours. After treating the cells with Sn, one half of the cells were analyzed by GFAA, the other half by EMI. GFAA results are contrasted to EMI results in Table II. 

Figure 5. Kinetics of Sn uptake by Pseudomonas 244 measured by EMI (A) and GFAA ( )[Sn ] = 10 ppm In water.

Several attempts were made to monitor the uptake of Zn as a function of time. As a first attempt, the cells were exposed to 30 ppm Zn at room temperature. The rate of uptake of the Zn by the cells was much faster than was the case with Sn it was impossible to measure an increase in zinc content of the cells above that of the initial Zn -exposed sample either in florescence signal or GFAA signal by the methods described in this work. Reducing both the concentration of Zn in solution (10 ppm and 1 ppm) and the temperature (0°) did not slow down the uptake process enough to monitor an increase in accumulated Zn. By addition of known concentrations of Zn to the cells exposed to a 1.0 ppm Zn solution, it was found by GFAA that the amount of zinc accumulated... 

Determination of Noble Metals in Ore Samples by GFAAS-HPTLC... 

The strong selectivity of A A -dialkyl A-benzoylthiourea toward platinum metals has been favorably exploited to determine noble metals (Rh, Pd, Pt, and Au) in samples of ore and rocks by graphite fnmace atomic absorption spectroscopy (GFAAS) and UV detection after liquid chromatographic separation on silica HPTLC plates [23]. The results are presented in Table 14.3. 

Because of their growing importance during RM production, methods that need only milligram samples, like NAA and solid-samphng GFAAS, will be subsequently discussed in some detail see also Section 4.3. 

Cadmium and lead profiles in birds feathers based on samples in the milligram range and below were determined by solid sampling Zeeman-GFAAS, using a feather RM produced by milling at liquid nitrogen temperatures and characterized for its metal contents with different analytical methods (Hahn et al. 1990). 

Hahn E, Hahn K, Mohl C, Stoeppler M (1990) Zeeman SS-GFAAS - an ideal method for the evaluation of lead and cadmium profiles in bird s feathers. Fresenius J Anal Chem 377 306-309. 

Noweoy R, Marr IL, Ansari TM, Muller H 1999) Direct analysis of solid samples by GFAAS -determination of trace hea-vy metals in barytes. Fresenius ( Anal Chem 364 533-540. 

Four types of atomic spectrometry have been interfaced for chromatographic detection, namely AAS, FES, AFS and APES. Ebdon et al. [178] have discussed coupling of HPLC with AAS. HPLC-FAAS is relatively insensitive. Application of HPLC-GFAAS or... 

Practically all classical methods of atomic spectroscopy are strongly influenced by interferences and matrix effects. Actually, very few analytical techniques are completely free of interferences. However, with atomic spectroscopy techniques, most of the common interferences have been studied and documented. Interferences are classified conveniently into four categories chemical, physical, background (scattering, absorption) and spectral. There are virtually no spectral interferences in FAAS some form of background correction is required. Matrix effects are more serious. Also GFAAS shows virtually no spectral interferences, but... 

GC-GFAAS interfacing. HPLC-GFAAS has also been reported. 

In industrial research laboratories, AAS (in particular FAAS) is no longer being used to the same extent as in the past, despite the aforementioned important improvements in AAS technology. More rapid, multi-element methods have gradually taken over, such as ICP-AES, ICP-MS and NAA. However, the determination of one element is faster with AAS than with an ICP technique. Also, ICP-AES does not supersede GFAAS in terms of sensitivity and selectivity. 

Multi-element AAS has been reviewed [112], as well as ETAAS [104] and instrumental aspects of GFAAS [113]. Various monographs on analytical atomic absorption spectrometry are available [52,96,114,115], and on GFAAS [116] and ETAAS [117] more in particular. 

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