ABSTRACT
Flame photometry is now the usual means of measuring sodium and potassium, and commercially made flame photometers will measure about 0·2 μmol of either ion in about 2 ml of solution to about 1 %. However, the prior dilution of biological samples is necessary and the minimum quantity for measurement is set by the time constant of the measuring circuit. Specialized flame photometers have been described which extend the detection limit to 10−14 mol (Müller, 1958; Ramsay, Brown & Falloon, 1953), but these are hardly suitable for routine work. This communication describes inexpensive modifications for use with commercial flame photometers which avoid prior dilution of the samples and give a tenfold improvement in the detection limit, defined as the smallest quantity of an ion which may be detected with a 95 % certainty.
