Extending the working range for the flame photometric determination of alkali metals and calcium using the PAVLIN spectrometer

At the Novosibirsk Chemical Concentrates Plant, the determination of alkali metals and calcium in the range of 0.1–100 mg/l is carried out using atomic emission spectra excited in an air-acetylene flame and recorded in the range of 390–860 nm. When these elements are analyzed simultaneously in a wide range of concentrations, the accumulation time of the analytical signal (exposure) is determined by the minimum concentration of calcium. However, at this exposure, the highly sensitive lines of sodium and potassium do not provide the analysis in the entire concentration range, since at large values, the analytical signal goes into saturation. Other analytical lines of potassium and sodium in the above-mentioned operating spectral range have three to four orders of magnitude lower sensitivity. As a result, there may be a gap in the range of detectable concentrations. This paper provides a way to eliminate this gap. To evaluate the degree of correction of the recorded signal, the relative intensities of the spectral lines of potassium and sodium excited in an air-acetylene flame are calculated. Then, based on the calculation results, an optimal echelette diffraction grating with a blaze angle of 300 nm is selected, and a combination of filters is installed to equalize the recorded radiation. As a result, for sodium and potassium, for which the determination is carried out along two analytical lines, the calibration dependences have an overlap that includes at least two concentration values.