Improved microdroplet method for quantitative X-ray microanalysis of small fluid samples

A simple method of using an internal standard for X‐ray microanalysis of microdroplets

“…We also show that microdroplets can be rapidly air‐dried and that slow drying or lyophilization is not neccesary. These changes to the Rippon et al . (1993 ) modification of the Hyatt & Marshall (1985) method provide a simpler and more accurate procedure.…”

“…The microscope had two liquid‐nitrogen‐cooled anticontamination traps which effectively cryopumped the column to give a vacuum of < 1.3 × 10 −5 Pa in the specimen chamber. No evidence of contamination was evident under these conditions ( Rippon et al ., 1993 ). Spectra were processed using the Link FLS (filtered least squares fitting) software to obtain peak integrals.…”

“…The analysis of microdroplets by X‐ray microanalysis has proved to be an accurate method for obtaining elemental concentrations in very small volumes of biological fluids ( Quinton, 1979; Bonventre et al ., 1980 ; Morgan, 1983; Hyatt & Marshall, 1985; Bostrom et al ., 1988 ; Roinel, 1988; Rippon et al ., 1993 ). Microdoplets have been analysed in microprobe instruments, scanning electron microscopes (SEMs) and transmission electron microscopes (TEMs) ( Morgan & Winters, 1993).…”

“…In this case the thin film model of X‐ray microanalytical quantification ( Russ, 1974; Cliff & Lorimer, 1975) can be applied. This depends on the use of an introduced internal standard and need not depend on the use of calibrated micropipettes ( Hyatt & Marshall, 1985; Rippon et al ., 1993 ). A series of ‘ k factors’, which account for the differences in X‐ray generation and detection of X‐rays from one element to another, are also required.…”

“…Cobalt has a number of disadvantages, the principal one being that it can cause precipitation of phosphates in the sample fluid. The disadvantages of cobalt were overcome by the introduction of rubidium as a reference element ( Rippon et al ., 1993 ).…”