Methanol in varying ratio was studied and the resolution (R) between two acids and interferences, and the run time of the chromatogram was taken into consideration. The optimization condition was performed using an isocratic elution at the proportion of 60:40 (v/v) 5 mM ammonium acetate aqueous solution adjusted to pH 4.4: methanol at a flow rate of 1 mL/min. The C18 column with 5 cm length was preferred as the complete separation was occurred within 3 min and the mobile phase operated was also 3 times decreased.
Under this condition, benzoic acid was
well separated from sorbic acid with good peak shape (resolution 3.62). Tailing factor was
0.96 and 1.00 and the number of the theoretical plates (efficiency) was 3029 and 3599 for benzoic acid and sorbic acid, respectively. The typical retention time of benzoic acid and sorbic acid was 1.82 and 2.32 min, respectively (Figure 2). Moreover, peaks of matrix interference in noodles were observed to separate from the peak of benzoic acid and sorbic acid (resolution > 2) (Figure 2 (B) and (D)). The overlaid diodearray spectrum showed good UV absorbance at 234 nm for benzoic acid and sorbic acid, and then this wavelength has been chosen for detection.