Silver detection

Highly sensitive iastmmental techniques, such as x-ray fluorescence, atomic absorption spectrometry, and iaductively coupled plasma optical emission spectrometry, have wide appHcation for the analysis of silver ia a multitude of materials. In order to minimize the effects of various matrices ia which silver may exist, samples are treated with perchloric or nitric acid. Direct-aspiration atomic absorption (25) and iaductively coupled plasma (26) have silver detection limits of 10 and 7 l-lg/L, respectively. The use of a graphic furnace ia an atomic absorption spectrograph lowers the silver detection limit to 0.2 l-ig/L. 

Glyoxal-based fixatives work faster than formalin. Small biopsies may be ready to process after only an hour while properly grossed larger specimens are ready in about 6h. Structural detail is remarkable in its clarity (Fig. 12.9). Red blood cells are lysed, but that rarely presents a problem. Eosinophilic granules are reduced in prominence (see below). Special stains work well, except for tests for iron (the mildly acidic pH is detrimental) and the silver detection methods for Helicobacter pylori. Most notably, glyoxal-fixed tissues retain strong immunoreactivity for most antigens. The chemistry behind most of this is known. 

The method of sol-particle immunoassay uses colloidal metal particles as the label. Typically these labels have been colloidal gold and colloidal silver. Detection in this type of assay is carried out visually, colorimetrically or by atomic absorption spectroscopy with electrothermal atomization. The colorimetric methods obviously offer potential in sensor development and the detection limits in the pmol 1 range are useful. 

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