d. Flame photometric measurement: Determine lithium concentration by direct intensity
measurements at a wavelength of 670.8 nm. The bracketing method (Section 3500-NaB.4d) can
be used with some photometric instruments, while the construction of a calibration curve is
necessary with others. Run sample, water, and lithium standard as nearly simultaneously as
possible. For best results, average several readings on each solution.
Follow the manufacturer’s instructions for instrument operation.