INAA

Instiximental neutron activation analysis (INAA) is considered the most informative and highly sensitive. Being applied, it allows detecting and determination of 30-40 elements with the sensitivity of 10 -10 g/g in one sample. The evident advantage of INAA is the ability to analyze samples of different nature (filters, soils, plants, biological tests, etc.) without any complex schemes of preliminai y prepai ation. 

Atomic absorption spectroscopy of VPD solutions (VPD-AAS) and instrumental neutron activation analysis (INAA) offer similar detection limits for metallic impurities with silicon substrates. The main advantage of TXRF, compared to VPD-AAS, is its multielement capability AAS is a sequential technique that requires a specific lamp to detect each element. Furthermore, the problem of blank values is of little importance with TXRF because no handling of the analytical solution is involved. On the other hand, adequately sensitive detection of sodium is possible only by using VPD-AAS. INAA is basically a bulk analysis technique, while TXRF is sensitive only to the surface. In addition, TXRF is fast, with an typical analysis time of 1000 s turn-around times for INAA are on the order of weeks. Gallium arsenide surfaces can be analyzed neither by AAS nor by INAA. 

Examples of the use of INAA in homogeneity testing of RMs are numerous and therefore only a few illustrative examples can be mentioned. More than ten elements can frequently be used for the accurate estimation of homogeneity of several types of biological materials (Tu and Lieser 1984), while a much higher number of elements can usually be precisely assayed in geochemical and environmental RMs. 

Becker DA (1993) Unique quality assurance aspects of INAA for reference material homogeneity and certification. Fresenius J Anal Chem 345 298-301. 

Kucera J, Sychra V, Horakova J, Soukal L (1997) Use of INAA in the preparation of a set of soil reference materials with certified values of total element contents. J Radioanal Nucl Chem Articles 215 l47-i55. 

Rossbach M, Grobecker KH (1999) Homogeneity studies of reference materials by solid sam-pling-AAS and INAA. Accred Qual Assur 4 498-503. 

Of the four strategies given above, the best condition for obtaining independent data for quality control (QC) are satisfied when INAA and RNAA results are compared, because the use of RNAA dramatically improves the selectivity of signal measurement and eliminates or greafiy reduces the measurement uncertainty sotuces, such as spectral interferences. A variety of radiochemical separations and... 

As an example of the capabilities of a combination of INAA and RNAA using a two group separation scheme for the simultaneous determination of As, Cd, Cu, Mo, Sb, Hg, and Se (Kucera and Soukal 1993), and a single separation procedure for vanadium determination (Byrne and Kucera 1991), Table 3.8 shows results for NIST-SRM-i573a Tomato Leaves that were obtained prior to certification of this material (Kucera 1995), and later on taken into consideration for deriving the NIST certified and information values (Becker 1995, personal communication). 

Tab. 3.8 INAA and RNAA results for NIST SRM-i573a Tomato Leaves (dry weight) (Kucera 1995)...

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