ORGANIC AND INORGANIC GASES by FTIR Spectrometry: METHOD 3800, Issue 1, dated 15 March 2003 - Page 3 of 47 PRE-TEST PROCED URES: The following procedures (Steps 1 and 2) may be performed only by an experienced “analyst” (see Append ix A ). 1.
Verify that the FTIR system has been tested for wavenumber reproducibility, minimum instrumental linewidth (MIL), absorption pathlength, system resp onse tim e, residual squared area (RSA ), and detector linearity as desc ribed in App end ix B. If the system is new and/or has been recently assembled and/or has been recently serviced, perform and document results of the tests described in Appendix B before proceeding. 2. Prepare a test plan. The plan must include the following: a. The proposed system configuration, including the absorption pathlength and integration time for sample spectra. b. The data quality objectives, ana lytical region s, and expected Limit of Detection (LOD) values for each ana lyte. See Ta ble 2 a nd A ppe ndix E for exa m ple values and calculations. c. The names of all “operators” and “analysts” to be involved in the test. Analysts must be experienced in all aspects of the test procedures listed below, and may perform any or all of the test procedures. Ope rators m ust be expe rienced in the perform ance of Steps 3 through 13 listed below, and may perform only those portions of the test procedures. d. Verification that the system configuration, existing RS A values, and related LO D values are consistent with the test’s d ata quality objectives . (See App end ix E, Section 3.)
The follow ing p roce dures (Ste ps 3 throu gh 13) m ay be perfo rmed by a n experienced operator or analyst. 3. Activate the FTIR system according to the m anu fac turer ’s instruction s. A llow suffic ient tim e for the infrared source, the infrared detector, and (if required) the temperature control systems to stabilize. 4. Verify that the computer system is programm ed to store interferogram s; if the available data storage cap acity is insufficient for storage of all interferogram s, store single beam spectra instead. Verify adequacy and performance of the (recomm ended) data backup system. 5. Bypassing the sampling system, flow N 2 or zero air directly into the infrared absorption cell until a sta ble infrared response and moisture levels are reached. Record a background spectrum using an integration time equal to or greater than that planned for subsequent sample spectra. 6. Use the entire FTIR system (including all sampling components) to record an absorbance spectrum of a sam ple stream of N 2 or zero air. Use the integration time planned for subsequent sample spectra. Verify that the sam ple flow rate m eets or ex cee ds that specified in the syste m res ponse tim e documentation. Examine the resulting “system zero” (SZ) spectrum and verify the absence of contaminants in the sampling system and infrared absorption cell. If contaminants are detected, clean or replace the appropriate sampling system com ponents and/or infrared absorption cell and record a new SZ spe ctrum . If contam inants ca nno t be eliminated , the tes t resu lts and LOD values may require revision during the qua lity control proce dure s (see S teps 14 throug h 17 ).
CALIBRATION: 7. Using the entire sampling system, acquire two or more pre-test CTS spectra and use them to calculate the system absorption pathlength LS (see Appendix B, Section 1). Use the integration time planned for sub seq uen t sam ple sp ectra . Verify tha t L S is within 5% of the value quote d in the tes t plan. Verify that the sam ple tem pera ture a nd p ressure are within 10 to 30 °C and 725 to 795 m m Hg, resp ective ly. 8. W hen possible, perform the following system checks before sampling. If necessary, they may be delayed until performance of the (post-testing) quality control procedures (see Steps 14 through 17). If performed after sampling, the results of these procedures may require revision of the test results and LODs. a. LOD Check. Using one of the SZ spectra, calculate the RSA values (see Appendix B, Section 2) and LOD values (see Ap pendix E, Sec tion 2) in the analytical regions pertaining to the test analytes. Verify that the system pathlength, current RSA values, and current LODs are c ons istent w ith the test’s da ta quality objectives (see App endix E, Section 3).
NIOSH Manual of Analytical Methods, Fourth Edition
