Effects due to the type of glass used in the discharge tubes on the calibration of emission spectrometers for the measurement of nitrogen-15
The influence of the type of glass used in the discharge tubes on the calibration of a spectrometer that is used for the measurement of nitrogen-15 by emission spectrometry has been investigated. Discrepancies in the values obtained for the same experimental samples measured with a Statron, Model NOI-5, emission spectrometer and with a Model NOI-4 emission spectrometer were traced to the use, with the latter instrument, of sealed glass calibration standards supplied by the manufacturer and prepared with glass different from that supplied for the preparation of experimental samples.
Three consignments each of Pyrex and Rasotherm glass were used to prepare discharge tubes containing nitrogen gas at six different levels of known nitrogen-15 abundance. Both the type and the consignment of glass had a considerable effect on the values obtained for apparent nitrogen-15 abundance. By applying a simple calibration expression appropriate to each batch of glass, corrected values in good agreement were obtained.
Results for experimental samples measured with the NOI-5 and NOI-4 emission spectrometers were in good agreement when each instrument was calibrated with standards prepared from the same consignment of glass as was used for the experimental samples.