where “X” is the mean concentration of fortified sample blank values, and “s” is the sample standard deviation.
For recovery experiment, non-infected chilli samples were spiked with AFB1, AFB2, AFG1 and AFG2 at two concentration levels of 0.5 and 2 μg kg−1. Spiking was carried out in six replicates. The spiked materials were then analysed according to method protocol previously described and analytes were quantified. The observed signal was plotted against the actual concentration. The measured concentration was determined using the obtained calibration curves and the recovery value was calculated by the following equation:
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The accuracy refers to a combination of precision and trueness. The precision of the method in terms of repeatability was evaluated by six-replicated analysis of spiked samples at two concentrations (0.5 and 2 μg kg−1) of the analyte in the sample on the same day. The precision was calculated as the relative standard deviation (RSD) of replicate results. The trueness, in terms of bias (a measurement of systematic error) was calculated according to the following equation:
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where “Xi” is the expected value and “Xt” is measured value.
3. Results and discussion
3.1. Analytical method performance
The calibration level, linear regression equation and coefficient of determination (R2) for each analyte are shown in Table 1. Based on linear regression analysis, all analytes showed good linearity over a concentration range of 0.1–5 μg l−1, with coefficient of determination greater than 0.9994. Fig. 1A shows an HPLC-FD chromatogram of AFs standard solution containing 2 μg AFB1 l−1, 2 μg AFB2 l−1, 2 μg AFG1 l−1 and 2 μg AFG2 l−1.