The validation studies for such purposes as maximizing the sensitivity, reducing the measurement limits, creating a wide linear dynamic range and raising the degree of accuracy and precision were realized by examining basic assay parameters such as precision, accuracy, linear region
range, limit of detection (LOD) and the limit of quantification (LOQ).
The precision of the method was tested by considering intra-day and inter-day repeatability. For this purpose, corn oil samples which of FFA content ranged from 0.09 to 2.42 % oleic acid were injected for three consecutive days (n = 5), and the results were evaluated statistically regarding mean (X), standard deviation (SD), and relative standard deviation (RSD %). They are tabulated in Table 1.
The results in both cases (intra- and inter-day) indicated high precision, as the percent RSD did not exceed 2 %.
The accuracy of proposed method was tested by analyzing the working references corn oil samples with the % FFA values ranging between 0.09 and 2.42 % oleic acid.
Intra- and inter-day recovery studies were performed for each oil sample (n = 5) and the average percentage recovery were found to be within the range of 87.19–122.22 % by proving the accuracy of proposed FIA method (see Table 1).
The linearity of the proposed method was evaluated by linear regression analysis using six different FFA concentrations of corn oil samples. Each concentration was measured five times and the proposed method was found linear between 0.09 and 1.50 oleic acid % FFA ranges.
The results of linearity test such as slope, intercept, correlation coefficient of the linear line and standard deviation of slope and intercept were presented in Table 2.
For the calculation of LOD and LOQ values, calibration graphs (area-% FFA) were used, with points plotted for corn oil sample. The standard deviations of the areas and FFA values were calculated by using the slope and intercept of the graph and coefficient of variation (CV) values.
FFA values, corresponding to three and ten times the calculated standard deviation value, were regarded as LOD (3 s) and LOQ (10 s), respectively. Accordingly, LOD values for corn oil was calculated as 7.41 9 10-3 oleic acid %, and LOQ values were calculated as 2.24 9 10-2 oleic acid %, respectively.