ISO 9647:2020 pdf download – Steel – Determination of vanadium content – Flame atomic absorption spectrometric method (FAAS)
6.1 Atomic absorption spectrometer
The spectrometer shall be equipped with a vanadium hollow-cathode lamp and supplied with dinitrogen monoxide and acetylene sufficiently pure to give a steady clear fuel-lean flame, free from water and oil, and free from vanadium. The atomic absorption spectrometer used will be satisfactory if, after optimization according to 8.3.3, the limit of detection and characteristic concentration are in reasonable agreement with the values given by the manufacturer and it meets the performance criteria given in 6.1.1 to 6.1.3. The instrument should also conform to the additional performance requirement given in 6.1.4.
6.1.1 Minimum precision (see Annex C)
The standard deviation of 10 measurements of the absorbance of the most concentrated calibration solution shall not exceed 1,0 % of the mean absorbance of this solution. The standard deviation of 10 measurements of the absorbance of the least concentrated calibration solution (excluding the zero member) shall not exceed 0,5 % of the mean absorbance of the most concentrated calibration solution.
6.1.2 Limit of detection (see Annex C)
The limit of detection is a number, expressed in units of concentration (or amount) that describes the lowest concentration level (or amount) of an element that can be determined to be statistically different from an analytical blank. The limit of detection of vanadium in a matrix similar to the final test solution shall be less than 0,3 µg/ml.
6.1.3 Calibration linearity (see Annex C)
The slope of the calibration line covering the top 20 % of the concentration range (expressed as a change in absorbance) shall not be less than 0,7 times the value of the slope for the bottom 20 % of the concentration range determined in the same way. For instruments with automatic calibration using two or more standard solutions, it shall be established prior to the analysis, by obtaining absorbance readings, that the above requirements for calibration linearity are fulfilled.
6.2 Ancillary equipment
Scale expansion can be used until the noise observed is greater than the readout error and is always recommended for absorbances below 0,1. If scale expansion has to be used and the instrument does not have the means to read the value of the scale expansion factor, the value can be calculated by measuring a suitable solution with and without scale expansion and then dividing the signals obtained.
8.3.3 Adjustment of the atomic absorption spectrometer
Fit the vanadium hollow-cathode lamp (see 6.1) to the atomic absorption spectrometer (6.1), switch on the current and allow it to stabilize. Adjust the wavelength in the region of 318,4 nm to minimum absorbance, if possible. Following manufacturer’s instructions, fit the correct burner, light the flame, adjust it to a red feather and the observation height in the flame to about 20 mm and then allow the burner temperature to stabilize. Taking careful note of the manufacturer’s instructions regarding the minimum flow rate of acetylene, nebulize alternately the calibration solution of highest concentration and the zero member, adjust the gas flow and burner position (horizontally, vertically and rotationally) until the difference in absorbance between the calibration solutions is at a maximum. NOTE Other suitable radiation sources can also be used.