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Discrepancies in the calibration of reaction rate analysers

Journal of Automatic Chemistry
Hindawi Publishing Corporation
Publication Date
DOI: 10.1155/s1463924680000284
  • Research Article
  • Biology
  • Chemistry
  • Design


Discrepancies in the calibration of reaction rate analysers E. F. Legg* Department of Cinical Chemistry, East Birmingham Hospital, Birmingham, England. J. D. Cooper Department ofBiochemistry, Coventry & Warwickshire Hospital, Coventry, England. M. R. Holland Department ofChemical Pathology, New Cross Hospital, Wolverhampton, England. J. Willis Department ofMedical Engineering, East Birmingham Hospital, Birmingham, England. Introduction Problems were encountered in ascertaining the cause of dis- crepancies between two LKB reaction rate analysers (RRA). One of the instruments consistently gave results which were 15% less than the values obtained from the other. The calibration procedure provided by the manufacturer, how- ever, was not helpful in deciding at what level the fault was operating. This paper describes the investigation of the factors responsible for the discrepancy. A calibration method is proposed which is designed to ensure better inter-laboratory agreement of enzyme analyses and which can be adapted to the calibration of any reaction rate analyser. Preliminary investigations An initial investigation showed the calibration differences noted were not related to the reagent concentrations. Similarly, differences in pump volumes, incubator tempera- ture, recorder voltages, chart speeds and cuvettes could not account for a difference between the instruments of greater than about 2%. The focussing of the incident light beam onto the circular cuvette was also found to be correctly aligned. Filters A 5 nm difference was found between the peak absorbances of the original 340 nm filters used in the LKB reaction rate analysers. When both sets of filters were compared in the one instrument by means of an enzyme assay, they gave mean activities values 107.8 + 5.6 (n 10) and 103.8 + 5.8 (n 10) IU/L for the same-test. This difference was significant at the 0.001 level and accounted for nearly 5% of the discrepancy between the instruments. All filters in subsequent studies were chosen with peak

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