INSTRUMENT MAINTENANCE PRACTICAL TASK P9. IR CELL THROUGHPUT Outline Sodium chloride as a cell material for the infrared region has the disadvantage of being water‐ soluble. Not only does this limit what solutions can be run, but also means that atmospheric moisture will be absorbed and reduce the transparency of the plate. Affected salt plates can be polished, which removes the damaged top surface layer. Procedure 1. Run an air blank. 2. Place a loose NaCl plate in the holder, insert into the instrument and run the spectrum from 4000‐600 cm‐1. 3. Determine the highest and lowest %transmittance values. Acceptable results: Must be >90 %T across the entire spectrum Maximum variation in %T is 3% Reporting Requirements Use the standard Performance Check reporting sheet.