Comparison between the precision of measurements in two types of the micropipettes according to CLSI EPS and ISO 8655

ABSTRACT

In the diagnosis medical labs, it is very important to evaluate the precision of micropipettes in transferring small amounts of liquids. The medical tests will not result accurately, if the liquid volume doesn't transfer exactly by micropipettes. Thus the doctor faces sort of problems in the disease diagnosis and its control. In the standard CLSI EPS, there is a method to specify and assess the precision of micropipettes, by using CV [coefficients of variation]. Also there are other methods to estimate and test the mention CV theory, in the formal statistic texts which could be used to assess the micropipettes precision. It is the main goal of this research to study the precision of lab micropipettes which are shown by A and B and compared by reference standard value from ISO 8655. In this research we evaluate the precision of the lab micropipettes. Two brands A and B are assigned to measure the distilled water mass by using the accurate scale which is accurate up to 10-6 to measure 50 gram weight. The experimental eenvironment is a metrology lab which is confirmed by Iran Standard and Industrial Researches. A unique technician sampled in the beginning of the work time and after 2 hours repeated the sampling. Totally, each micropipette is used to measure 40 times with 10 times repeat for single measurement in 28 work days. It is used common statistical methods to estimate and test the coefficients of variation theory. Point estimation of CV for micropipettes A and B were 0.50% and 0.64% respectively. Also the 95% confidence upper bounds for these two micropipettes by using likelihood ratio method were 0.53% and 0.64% respectively. The micropipette A confirmed the ISO 8655, but the micropipette B did not. Measurement error in micropipette B was 30% less than micropipette A in average. By using the approach of CLS EP5 and confidence interval for CV, precision of two micropipettes were compared. Only one of them confirmed the ISO 8655, but the other one was failed