3.5. Linearity
Linearity was established by least squares regression analysis
of the calibration curve. Calibration curve for the assay
method was obtained over the calibration range from 80%
to 160% of assay concentration (0.1 mg/mL). The correlation
coefficient (r) was greater than 0.9998. The results show that
an excellent correlation exists between the peak area and concentration
of the analyte. The regression equation is as follows:
y ¼ 188117x þ 80:146 ð1Þ
Linear calibration plots for the 4-epianhydrotetracycline
hydrochloride limit method was obtained for three sets of concentrations
each cover the concentration range from 50 to
150% of the limit concentration 3 lg/mL. The correlation
coefficients (r) obtained were greater than 0.997. The regression
equations for the three sets were as follows:
y ¼ 39158x þ 9017; r ¼ 0:998 ð2Þ
y ¼ 42625x þ 6214; r ¼ 0:997 ð3Þ
y ¼ 40984x þ 1844; r ¼ 0:999 ð4Þ
The results met the specified acceptance criteria for the
assay procedure (r is not less than 0.999) and for the limit procedure
(r is not less than 0.99).