FLAME PHOTOMETRIC ANALYSIS OF SODIUM AND POTASSIUM IN NANOGRAM SAMPLES OF MAMMALIAN NERVOUS TISSUE

A dual-channel integrating micro-flame-photometer was evaluated for simultaneous analysis of sodium and potassium in aqueous extracts from nanogram samples of frozen-dried mammalian nervous tissue. Calibrated quartz constriction micropipettes delivered 10⁻⁸ l. of extraction fluid to a 100 μ platinum-iridium wire for insertion directly into the flame. Over-all reproducibility was 4 per cent for twenty samples containing 6.5 × 10⁻¹¹ g K and 2.2 × 10⁻¹¹ g Na. Large amounts of anions decreased the emissions for both sodium and potassium, but no interference between sodium and potassium was found over the range adopted for biological analyses. The micro-flame-photometer gave results for a few nanolitres of aqueous extracts of brain homogenates which were within 3-5 per cent of those obtained on larger volumes with a conventional flame photometer. Macroanalysis and microanalyses of microgram quantities of frozen-dried tissue sections of cerebral cortex were also in agreement. Nanogram samples from frozen-dried spinal ganglia of a rabbit gave average values for sodium and potassium (calculated/g wet wt.) which were similar to those for aqueous extracts of rabbit brain homogenates. Samples from peripheral ganglia in vivo, 10 minpost mortem and 20 min post mortem had significantly different average K/Na ratios of 1.97, 2.64 and 3.23, respectively.