Arsenic instrumental neutron activation analysis

Instrumental neutron activation analysis was used to determine concentrations of several major and trace elements in samples of heavily corroded residues found in crucible fragments excavated at Tel Dan, Israel. The residues were mostly hard, metallic phases admixed with nonmetallic inclusions that appeared to be ceramic material from the loose porous interior of the crucible itself The objective was to identify the metals that had been melted in these crucibles. A method is described that attempts to separate nonmetallic and metallic phase data. In comparison to previous reports on analyses of source materials thought to have been used at Dan in this period (Late Bronze II Age-Early Iron I Age 1400-1000 B.C.), high gold concentrations were found. These appear to be correlated to arsenic and antimony concentrations. This finding is discussed in relation to possible changes in the source of tin at this period. 

X-ray fluorescence spectrometry (XRF) and instrumental neutron activation analysis (INAA) are commonly used for multi-element analysis of rock, soil, and sediment samples since they do not require chemical dissolution. However, the detection limit for arsenic using XRF is on the order of 5 mg kg and is too high for many environmental purposes. Once dissolved, arsenic can be determined using many of the methods described above... 

The Trace Metals Project conducted a study to identify the type of container which would provide minimum losses of arsenic and mercury by precipitation, volatilization, adsorption, or diffusion. Solutions of organomercury and organoarsenic compounds added to petroleum feedstock were used. Because of the relative ease with which mercury and arsenic can be determined at sub-parts-per-million levels in a hydrocarbon matrix by instrumental neutron activation analysis (INAA), this technique was used for the analytical measurements. The solutions were stored in five different types of glass and/or plastic containers and sampled periodically over eight months (12). The results of the study are summarized in Tables 2.III and 2.IV. 

Arsenic levels below 10 ng/g can be readily detected in petroleum by instrumental neutron activation analysis. The most convenient technique involves direct gamma counting based on the 75As (n, y) 76As reaction with a principle radiation of 559 keV. After a 1-hr irradiation at a neutron flux of 1012 n cm"2 sec-1, the arsenic may be counted in a relatively short time. The method requires a high resolution Ge(Li) detector to avoid interference from bromine (550 keV) or antimony (564 keV). 

Figure 3 Instrumental methods for the determination of arsenic compounds (Abbreviations AAS, atomic absorption spectrometry APS, atomic fluorescence spectrometry CE, capillary electrophoresis GC, gas chromatography HG, hydride generation ICP-AES, inductively coupled plasma-atomic emission spectrometry ICP-MS, inductively coupled plasma-mass spectrometry INAA, instrumental neutron activation analysis LC, liquid chromatography MS, mass spectrometry).

Elson, C.M., Ackman, R.G. and Chatt, A. (1983) Determination of selenium, arsenic, iodine and bromine in fish, plant and mammalian oils by cyclic instrumental neutron activation analysis. J. Am. Oil Chem. Soc. 60, 829-832. 

The detection limits of the old methods for the determination of arsenic (10) were too high to determine arsenic in uncontaminated biological samples. With the invention of instrumental techniques, such as flame atomic absorption (emission) spectrometry, graphite furnace atomic absorption spectrometry, neutron activation analysis, inductively coupled plasma atomic emission spectrometry, and inductively coupled plasma mass spectrometry, the ubiquity of arsenic in our environment was proven. The improvement of the analytical techniques has changed the reputation of arsenic from a poisonous substance to an essential trace element at least for warm-blooded animals (11). An arsenic requirement for humans cannot be deduced from these animal experiments. In recent literature, there are certainly more hints that arsenic might be an essential trace element for humans, but there is still a lot of future research work necessary to prove this. 

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