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• Sudan IV GC 6 × 10 −7 –9 × 10 −4 3 × 10 −7 6 Sudan IV Nanotube modified electrode 3 × 10 −7 –6 × 10 −5 6 × 10 −8 6 Sudan IV HPLC-DAD 3 × 10 −7 –6 × 10 −6 5 × 10 −8 3 Sudan IV Graphene-modified electrode 0 × 10 −7 –0 × 10 −5 0 × 10 −8 This work Analytical application Ketchup and chili sauce purchased from a local market were accurately weighed (10.0 g) and added to a stoppered flask with absolute methanol (50 mL) under sonication for 30 min. The combined extracts were centrifuged at 12,000 rpm to obtain the supernatant, which was collected followed by appropriate dilution with electrolyte solution to furnish a desired concentration for the sample analysis. Under the optimized conditions, the prepared test solution was detected at the graphene-modified GCE by CV. Fortunately, no observable peaks appeared and a recovery experiment was carried out by adding a known amount of Sudan IV to the sample. Recovery was calculated with reduction peak current values, and the results are shown in Table 2. The average recoveries (n = 6) varied from 96.8% to 99.2%, and the related RSD values were within the range of 1.51% to 3.78%. Table Recovery of determination of Sudan IV in samples (n = 6). No. Content in samples Sudan IV added (M) Average found (M) Recovery (%) R.S.D. (%) 1 Not detected 00 × 10 −7 91 × 10 −7 9 11 2 Not detected 00 × 10 −6 0.97 × 10 −6 0 78 3 Not detected 00 × 10 −6 87 × 10 −6 8 74 4 Not detected 00 × 10 −6 94 × 10 −6 2 82 5 Not detected 00 × 10 −5 97 × 10 −6 5 51 Interference The suitability of the graphene-modified GCE was tested for the determination of Sudan IV in food in the presence of potential interference (such as capsorubin, beta-carotene, zeaxanthin, violaxanthin, neoxanthin, lutein, and metal ion). These species differ greatly from Sudan IV in chemical structure and electrochemical characteristics, and no interference in the current response was observed for 2.0 µ M Sudan IV in the presence of 1000 times K + , Na + , Fe 3+ , Ca 2+ , and Mg 2+ ; or 100 times capsorubin, beta-carotene, leaxanthin, violaxanthin, neoxanthin, lutein, glucose, and ascorbic acid, indicating that the graphene-modified GCE is highly selective towards the determination of Sudan IV. Conclusions
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