Zinc determined in 10-microL serum or urine samples by flameless atomic absorption spectrometry

We describe a precise flameless atomic absorption spectrometric method requiring only 10 microL of sample, which thus permits repeated measurements in the neonate. Standard curves covering the range of 0 to 30 mg of zinc per liter, with standards in various matrixes (albumin, glycerol, serum, or nitric acid) had slopes ranging from 0.49 to 1.17, relative to that for aqueous standards. We prepared low-zinc matrixes, which had slopes similar to that of serum, by dialyzing serum or a 50 g/L solution of albumin vs a buffered zinc-free dialysis fluid containing appropriate inorganic constituents. Use of thoroughly de-ionized water, reagent-grade chemicals, "ultrapure" nitric acid, specified disposable plastic ware, and appropriate pipet tip-rinsing techniques minimized extraneous contamination with zinc. Concentrations of zinc in serum calculated from a "rational-method" calibration algorithm fit to the standard curve agreed well with independent determinations by flame atomic absorption spectrometry.