Sulphites analyzer in fruits, vegetables and their products towards export promotion strategy

In this work, two systems of sulphites analysis were designed and invented based on 3 reactions; firstly, sulphite (SO32-) is converted to volatile sulphur dioxide (SO2) by acidification, then, Fe (III) is reduced to Fe (II) by SO2, and finally, Fe(II) react with o-phenanthroline to form a red complex. All results of sulphite determination in this study were evaluated in mg L-1 as SO2 following the general regulations of sulphite amounts. The first system applied the headspace microextraction (HS-ME) incorporating to a lab on cotton swab platform with smartphone detection. A universal clamp sample holder was designed and fabricated for use with a microfluidic cotton swab-based analytical device (µCSAD) on a smartphone. The reactions were performed in 1.5 mL-vial, SO2 gas was diffused into the cotton head of the swab that hung over the sample solution, then reacted with the colorimetric reagent in the cotton. The red complex was detected by the smartphone. The linear ranges were 0.32–2.40 (R2 = 0.9997) and 2.4–24.00 mg L1 (R2 = 0.9936). The limit of detection (LOD) and limit of quantitation (LOQ) was 300 and 600 g L1, respectively. Compared to the Ripper method, the developed method showed no significant differences in the amount of SO2 in 13 bottles of wine samples. This µCSAD was simple, cost-effective, and eco-friendly. Moreover, the designed universal clamp holder and the software application can be used with multiple brands and models of smartphones. The second system, an automatic flow-based analysis via gas diffusion unit was invented, and the light emitting diode (LED 515 nm) and photodiode were used as a detection unit. The extraction time is an important role in controlling the rate of analysis by stopping the pump for 5 min to achieve an appropriate signal. This system presented a non-linear calibration graph, y = -0.1354x2 + 14.766x + 21.755 with R2 = 0.9991, in the range of 1.0-35.0 mg L-1. The LOD and LOQ were 0.32.and 1.08 mg L-1, respectively. The system was successful in the determination of sulphite in wines, coconut juice, and dried fruits. The amounts of sulphite were no significant different from those results analyzed by the iodometric titrimetric method. This system provided eco- and user-friendly with automated control.