Quantitative X-ray analysis of biological fluids: the microdroplet technique.
X-ray microanalysis can be used to quantitatively determine the elemental composition of microvolumes of biological fluids. This article describes the various steps in preparation of microdroplets for analysis: The manufacturing of micropipettes, the preparation of the specimen support, the deposition of droplets on the support, shock-freezing, and lyophilization. Examples of common artifacts (incomplete rehydration prior to freezing or partial rehydration after lyophilization) are demonstrated. Analysis can be carried out either by wavelength-dispersive analysis, which is the most sensitive method, or by energy-dispersive analysis, which is more commonly available. The minimum detectable concentration is 0.05 mmol.liter-1 for 0.1-nl samples analyzed by wavelength-dispersive spectrometry and 0.5-1 mmol.liter-1 for samples analyzed by energy-dispersive spectrometry. A major problem, especially in wavelength-dispersive analysis, where high beam currents are used, is radiation damage to the specimen; in particular chloride (but also other elements) can be lost. Quantitative analysis requires the use of standard solutions with elemental concentration in the same range as those present in the specimen.
Roinel
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Département de Biologie, CEA Saclay, Gif Sur Yvette, France.
D000818:Animals; D001826:Body Fluids / Q000032:analysis*; D002138:Calibration; D004577:Electron Probe Microanalysis / Q000379:methods*; D004864:Equipment and Supplies; D005612:Freeze Drying; D005615:Freezing; D006801:Humans; D008899:Mineral Oil; D014508:Urea / Q000032:analysis
D008899:Mineral Oil; D014508:Urea