Nondestructive analytical techniques sample size

Nondestructive radiation techniques can be used, whereby the sample is probed as it is being produced or delivered. However, the sample material is not always the appropriate shape or size, and therefore has to be cut, melted, pressed or milled. These handling procedures introduce similar problems to those mentioned before, including that of sample homogeneity. This problem arises from the fact that, in practice, only small portions of the material can be irradiated. Typical nondestructive analytical techniques are XRF, NAA and PIXE microdestructive methods are arc and spark source techniques, glow discharge and various laser ablation/desorption-based methods. On the other hand, direct solid sampling techniques are also not without problems. Most suffer from matrix effects. There are several methods in use to correct for or overcome matrix effects ... 

The question, what is it made of is more or less the standard inquiry analytical chemists are confronted with. However, even here the archaeological chemist has to handle intriguing and extraordinary situations which rarely occur elsewhere. The sample size is usually very small, and the methodology is often restricted to nondestructive techniques. 

In the laboratory, XRF analysis is usually performed in a vacuum chamber or in an atmosphere of an inert gas (like helium) so that low-energy photons are not absorbed by air. In general, the sensitivity of the method increases with the atomic number of the analyte and in solid samples the limit of detection for many elanents is typically in the mg kg" (ppm) range. One advantage of the technique is the ability to perform a nondestructive assay of several elements simultaneously, although the accuracy for quantitative analysis is quite limited. Due to their simplicity and small size, handheld XRF devices are available and can be carried into the field for onsite analysis as described in detail recently (Bosco 2013). 

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