It is possible for the interference filters to go bad.
Filters function to block certain wavelengths, allow others to pass, and to transmit a specified % of incident light. If the filters have deteriorated significantly there is typically a gradual change in peak areas, usually a decrease. Since the Lachat systems are calibrated frequently, the change is not always readily apparent. If one is having difficulty with a method and it is determined that the areas obtained for standards are significantly different than the Lachat method support data, the filter is a possible cause. In some cases, if a user goes back and looks at calibration areas over the last year or several months they may see that the areas have gradually changed over time. If another reason for a change in areas cannot be determined filter replacement should be considered.