Various methods of microchemical analysis for biology have been developed in conjunction with other recent advances such as the micropuncture technique. Few, however, have a sensitivity below 1VX2 gm.
Neutron activation is a successful means of ultramicroanalysis, and is applicable to biological samples. In this method, a sample is exposed to a neutron source and the resulting isotope can be identified by its decay rate, type of emission, and energy. The method is good for many elements, and for samples as small as lo-l4 gm, but the complexity of the necessary equipment and limitation of its use makes it impractical for many applications.
Another promising method developed in this laboratory is based upon the use of the electron microprobe x-ray analyzer. The probe, as it is often called, uses a beam of accelerated electrons to excite a sample, causing it to emit x-rays whose wavelengths are characteristic of the atomic number of the elements (l-3). A spectrometer, using a diffraction crystal, selects the wavelength; and the intensity of emission, measured with conventional x-ray detectors, is proportional to the quantity of the element being excited.
A method of analysis using the probe has several advantages. With it, one can detect any element whose atomic number is greater than five, and three elements can be analyzed simultaneously.
The sample may be in various forms, and the amount of the unknown element can be as low as 1V15 gm.
The following procedure was developed specifically for electrolyte analysis of renal tubular fluid and of plasma. Any other biological fluid could be analyzed similarly, though slight adaptations might be appropriate.
METHOD
The pipet developed for this method is made from Pyrex glass tubing (o.d. 3.5 mm, i.d. 2 mm), by first pulling to an inside diameter of about 54