Liquid Testing | 39
• The standard deviation for each set of readings should be less than the
allowed deviation.
Example: Absorbance readings of 1.950, 1.948, 1.955, 1.952, and 1.950
will result in a mean of 1.951, and a standard deviation of 0.0026. The
mean (1.951) multiplied by 1.0% (1.951 x 0.010) = 0.0195, which, when
added to the 0.005 (0.0195 + 0.005) = 0.0245 OD, which is the allowable
deviation. Since the standard deviation is less than this value, the
reader meets the test criteria.
Repeatability Specification:
± 1.0% ± 0.005 OD from 0.000 to 2.000 OD
± 3.0% ± 0.005 OD from 2.000 OD to 2.500 OD
Alignment Test
1. Using the plate prepared for the Linearity Test on the previous page,
conduct a Turnaround test by reading the plate
five times with the A1
well in the H12 position. Save the data after each read.
This test results in values for the four corner wells that can be used to
determine alignment.
2. Calculate the means of the wells A1 and H1 in the Normal plate position
(data from Linearity Test) and in the Turnaround position (from Step 1).
3. Compare the mean reading for well A1 to its mean reading when in the
H12 position. Next, compare the mean values for the H1 well to the same
well in the A12 position. The difference in the values for any two
corresponding wells should be within the accuracy specification for the
instrument.
Example: If the mean of well A1 in the normal position is 1.902, where the
specified accuracy is ± 1.0% ± 0.010 OD, then the expected range for the
mean of the same well in the H12 position is 1.873 to 1.931 OD. (1.902 x
1.0% = 0.019 + 0.010 = 0.029, which is added to and subtracted from 1.902
for the range.)
If the four corner wells are within the accuracy range, the reader is in
alignment.
Epoch Operator’s Manual
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