Statements on Instrument Comparability
No predetermined number of data pairs are used to make the assessment on data comparability between new and existing methodology. Even in the case of instrumentation with similar methods of detection (i.e., automated colorimetric), no specific number of data pairs is used. Comparability at low and high concentrations, salinity and other possible matrix interferences, sensitivity and precision are all factors in determining the number of pairs that must be addressed before bringing an instrument on-line and in determining instrument comparability.
The analyst who performs these comparisons should be experienced, open-minded and impartial. This person can give an evaluation of ease of instrument operation and a very important general statement of comparability. This statement on comparability must then be substantiated via statistical analysis of the data. As previously mentioned, these data must encompass the entire concentration range, matrix interferences, percent recovery, results of standard reference material analyses, etc. The data interpretation must support comparability. The analyst and laboratory QA/QC officer must concur and finally, some sort of presentation (written or verbal) must be given to the contractor explaining what procedure was followed and the results that were obtained to bring this instrument on-line.