Ultramicro (nanoliter range) determination of calcium concentration (10 −3m) by atomic absorption

An original ultramicro atomic absorption spectrophotometer is reported. Picomole amounts of calcium, in the nanoliter range volume were determined. Reproducibility, linearity, and recovery were statisfactory. No interference effects were observed from biological concentrations of Na, K, Mg, and Pi. Urea decreased the signal at concentrations above 0.1 m. Determinations were performed on late proximal renal tubular fluid and plasma ultrafiltrate samples obtained from three groups of rats: normal, acutely parathyroidectomized, and parathyroidectomized 2 days prior to the experiment. The results indicate a significantly higher tubular fluid to plasma ultrafiltrate calcium gradient in the acutely parathyroidectomized group. This spectrophotometer has several advantages, and disadvantages, as compared to the electron probe.