Samarium perchlorate is a particularly good reference for establishing wavelength calibration because it has useful peaks from 230 to 560nm, many having a spectral bandwidth of less than 5nm. The narrow bandwidth permits the precise locating of peaks. This is a great advantage over glass filters which may have a spectral bandwidth of over 30nm. Samarium is also an excellent material for checking wavelength in the UV as it has many peaks in the UV. In addition to wavelength calibration, the Samarium perchlorate can be used for checking instrument spectral bandwidth. By using peaks in the 230-240 or the 410-420 region, the ability of your instrument to resolve complex peaks can be tested.

Samarium presents a wide range of crisply resolvable peaks which are easily used to correlate the wavelength indicator on your spectrophotometer to the known Samarium peaks. The first procedure should be to scan the cell over the useable range to assure that all of the peaks can be resolved. Alter the slit width and scan rate to produce a useable spectra. Check each peak to assure that the reading on your spectrophotometer is within the manufacturer's tolerances for the wavelength of your spectrophotometer. If not, get a service technician to check and, if necessary, adjust your instrument. Samarium is measured against an air blank.

Periodically check the spectra, at a minimum in the area where you are doing your analysis. The periodic use of your Samarium cell will build a log of your instrument's wavelength accuracy for use with certification and troubleshooting should the correlation change over time.

Compare the wavelength peaks from your instrument with the expected values on the certificate supplied with the reference set. If the readings are within the expected range for your instrument then your wavelength scale is correct. If not, consult your service techincian and have the instrument evaluated

Each time that the analysis is repeated you can compare the new results with the previous results to check for any variance. If your instrument needs service because of a change in resolution, the historical data will greatly assist the service technician.