X2 values were similarly recorded for the
other standard AA solutions (20, 30, 40, and 50 ppm). X1 X2 values
were the absorbance of each working standard. The calibration
graph was constructed by plotting the absorbance values versus
the concentration (ppm) of standard AA solutions (r2 = 0.9951).
For the absorbance measurements of the sample extracts, the
same procedure was applied. First, an autozero operation for the
instrument was performed. Then, the absorbance of 1 ml of the
sample extract with 8 ml of distilled water and 1 ml of acetate buffer
solution was recorded at the end of 15 s. This was the X2 value
of the sample solution. X1 X2 values represented absorbance of
the sample. From the calibration graph, the AA concentration of
the sample was determined. All of the measurements were
recorded at 520 nm. All determinations were performed in triplicate
(n = 3).