Atomic absorption spectrometry using graphite furnace technique

A limited amount of work has been carried out on the determination of molybdenum in seawater by atomic absorption spectrometry and graphite furnace atomic absorption spectrometry [ 137,502], In a recommended procedure [503], a 50 ml sample of seawater at pH 2.5 is passed through a column of 0.5 g p-aminobcnzylccllulosc, then the column is left in contact with 1 M ammonium carbonate for 3 h, after which three 5 ml fractions are collected. Finally, molybdenum is determined by atomic absorption at 313.2 nm using the hot graphite rod technique. At the 10 mg/1 level, the standard deviation was 0.13 pg. 

The need for the determination of metallic constituents or impurities in pharmaceutical products has, historically, been addressed by ion chromatographic methods or various wet-bench methods (e.g. the USP heavy metals test). As the popularity of atomic spectroscopy has increased, and the equipment has become more affordable, spectroscopy-based techniques have been routinely employed to solve analytical problems in the pharmaceutical industry. Table 1 provides examples of metal determinations in pharmaceutical matrices, using spectroscopic techniques, and the reasons why these analyses are important. Flame atomic absorption spectrometry (FAAS), graphite furnace atomic absorption spectrometry... 

Flame atomic absorption spectrometry (FAAS) can be used to detect most elements present at levels greater than about 100 pg 1 . For more sensitive determinations graphite furnace atomic absorption spectrometry (GFAAS) is the technique of choice. In addition, if the volume of the fraction is limited GFAAS is ideally suited for the determination because only a few microfitres (5-20 pi) of sample... 

Other direct methods used more routinely for solid sampling analysis make use of an atomization cell, usually a graphite furnace, and optical spectrometry. Optical spectrometry techniques used are inductively coupled plasma (ICP) and atomic absorption spectrometry (AAS). This last technique, solid sampling atomic absorption spectrometry (SS-AAS), is used by far the most and thus will be dealt with more comprehensively. 

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. 

One of the advantages of the isotope dilution technique is that the quantitative recovery of the analytes is not required. Since it is only their isotope ratios that are being measured, it is necessary only to recover sufficient analyte to make an adequate measurement. Therefore, when this technique is used in conjunction with graphite furnace atomic absorption spectrometry, it is possible to determine the efficiency of the preconcentration step. This is particularly important in the analysis of seawater, where the recovery is very difficult to determine by other techniques, since the concentration of the unrecovered analyte is so low. In using this technique, one must assume that isotopic equilibrium has been achieved with the analyte, regardless of the species in which it may exist. 

Willie et al. [17] used the hydride generation graphite furnace atomic absorption spectrometry technique to determine selenium in saline estuary waters and sea waters. A Pyrex cell was used to generate selenium hydride which was carried to a quartz tube and then a preheated furnace operated at 400 °C. Pyrolytic graphite tubes were used. Selenium could be determined down to 20 ng/1. No interference was found due to, iron copper, nickel, or arsenic. 

Techniques for analysis of different mercury species in biological samples and abiotic materials include atomic absorption, cold vapor atomic fluorescence spectrometry, gas-liquid chromatography with electron capture detection, and inductively coupled plasma mass spectrometry (Lansens etal. 1991 Schintu etal. 1992 Porcella etal. 1995). Methylmercury concentrations in marine biological tissues are detected at concentrations as low as 10 pg Hg/kg tissue using graphite furnace sample preparation techniques and atomic absorption spectrometry (Schintu et al. 1992). 

Both flame and graphite furnace atomic absorption spectrometry are two of the commonest techniques used for the determination of metals and metalloids. Various authors " have discussed the application of both to the analysis of trace elements in biological materials. 

Graphite Furnace Atomic Absorption Spectrometry Graphite furnace atomic absorption spectrometry (GFAAS), the most popular form of ET-AAS, is today a common technique widely used in routine laboratories and has become a powerful tool for the analysis of trace and ultratrace elements in clinical and biological samples [61]. The main advantages of this technique are low cost, simplicity, excellent detection power, and the fact that it allows very low sample volumes to be used (5-20 p,L). In this sense, this technique allows LoDs for many elements in the order of 0.01 pgl-1 in solution or 1 pg g-1 in solid samples to be achieved [62]. However, the technique is prone to spectral and matrix interferences. 

Persson and Irgum determined sub-p.p.m. concentrations of DMAA in seawater by electrothermal atomic absorption spectrometry. Graphite-furnace atomic absorption spectrometry was used as a sensitive and specific detector for arsenic. The technique allowed DMAA to be determined in a sample (20 ml) containing a 10 -fold excess of inorganic arsenic with a detection limit of 0.02ng As ml ... 

A number of analytical techniques have been used to determine ppm to ppt levels of vanadium in biological materials. These include neutron activation analysis (NAA), graphite furnace atomic absorption spectrometry (GFAAS), spectrophotometry, isotope dilution thermal ionization-mass spectrometry (IDMS), and inductively coupled plasma atomic emission spectrometry (ICP-AES). Table 6-1 summarizes the analytical methods for determining vanadium in biological materials. 

Emission spectrometry using chemical flames (flame atomic emission spectrometry, FAES) as excitation sources is the earlier counterpart to flame atomic absorption spectrometry. In this context emission techniques involving arc/spark and direct or inductively coupled plasma for excitation are omitted and treated separately. Other terms used for this technique include optical emission, flame emission, flame photometry, atomic emission, and this technique could encompass molecular emission, graphite furnace atomic emission and molecular emission cavity analysis (MEGA). 

Interest in the roles of both essential and non-essential trace metals in human health and disease has undergone an enormous expansion in the last thirty years. This has come about partly due to major advances in our knowledge of inorganic biochemistry (Frausto da Silva and Williams. 1991), as well as the wider introduction into clinical laboratories of powerful analytical techniques such as graphite furnace atomic absorption spectrometry (Delves, 1987 Slavin, 1988). Developments in instrumentation and chemical matrix modification techniques have also brought about dramatic improvements in analytical performance (Delves. 1987 Baruthio et al.. 1988 Slavin, 1988 Christensen et al., 1988 Savory and Wills, 1991). Other analytical techniques, such as inductively-coupled plasma emission spectrometry (ICP) and ICP-mass spectrometry are also finding wide application in the clinical analysis of trace elements (Kimberly and Paschal, 1985 Delves and Campbell, 1988 Melton et al., 1990). Although the cost of such Instruments tends to restrict their use only to specialist centres, they have very important roles as reference techniques in the characterisation of reference materials (Delves and Campbell, 1988). 

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