During calibration experiments it was revealed that
the standard deviation of area ratio of CC standards
increased with concentration indicating a need for
weighted linear regression. The area ratios from cali
bration experiments are depicted in Table 1. The use of
the unweighted regression calibration model which re
sulted in equation y = 0.001x + 0.020, also resulted in
heteroscadasticity and a large total % RE. When
weighting factor of 1/x was used, the variances of area
ratios of CC standards were homogenized over the cal
ibration range with a decrease in the % RE. Thus,
weighted linear regression with a weighting factor of
1/x was selected as a calibration model which resulted
in the equation y = 0.0012x + 0.0298. During the val
i