X-ray microanalysis of pyroantimonate-precipitable cations.

Modifications of the Komnick potassium (pyro)antimonate precipitation method have been widely used for the subcellular localization of a variety of cations. The identity of cations precipitated with this method has often been controversial, and it is therefore important to establish definitive criteria for identifying precipitated cations in situ. In the present study, we have precipitated antimonate salts in vitro and examined the salts both in crystalline powder form and after embedment in Epon, using energy-dispersive X-ray microanalysis, in an attempt to identify biologically important antimonate-precipitable cations. We have found that the cations sodium, magnesium, and calcium, if present in physiological concentrations, will precipitate antimonate under "standard" conditions (2.5% antimonate, pH 7.2 - 7.4, in the presence of 1% OsO4). Characteristic X-ray emissions were observed for sodium and magnesium, as well as for lead similarly precipitated, but Lalpha and Lbeta emission peaks from antimony interfered with calcium identification and necessitated complex computerized deconvolution or peak stripping to determine the presence of a calcium peak. Precipitates of sodium did not contain appreciable potassium, whereas variable amounts of potassium were present in precipitates of calcium and lead, depending upon the extent of washing prior to dehydration. Sizeable potassium peaks were consistently present in even well washed magnesium precipitates. X-ray spectra of standardized precipitates were found useful as an aid in interpreting the more complicated spectra obtained from tissue samples.