การพัฒนาชุดตรวจวัดไนเตรทและไนไตรท์ราคาประหยัด

Abstract

Cost effective colorimetric test kits were successfully developed for nitrate and nitrite detection. The developed test kits were inexpensive, simple, small size and portable for on-site detection with low risk from chemical hazardous. Nitrite test kit was developed based on the entrapment of Griess reagents within poly vinyl alcohol (PVA) hydrogel matrix with poly ethylene glycol diglycidyl ether (EGDE) as a cross-linker. The polymeric sensor was fabricated on 24-well plate in a freezer 24 hours resulting in a clear gel and colorless. When standard solution of nitrite (1.5 mL) was dropped on the polymeric sensor, pink violet product was obtained. For nitrate test kit, it was developed based on the reduction of nitrate to nitrite by zinc powder which was entrapped within tapioca starch film. The film was fabricated on the lid of small plastic tube by incubating the polymeric mixture (zinc powder and starch solution) at 120°C for 15 minutes. The lid containing gray thin film with 8.36 μm thickness could be used to reduce nitrate to be nitrite before testing of nitrite with the nitrite test kit. The test kits were used in conjunction with digital image colorimetry (DIC) to demonstrate the rapid quantitative analysis of nitrate and nitrite. Red-Green- Blue (RGB) intensities of the pink-violet products obtained from the reaction between standard solutions and test kits were analyzed using custom-built color analysis application on smartphone. These RGB color data from the color product were used to establish calibration graphs. The blue intensity provided the most sensitivity for nitrite detection (20.6 ± 1.2 a.u./(mg)), while red channel was observed for nitrate detection (3.8 ± 0.1 a.u/mgL-1)). The intra-day precision for analysis of nitrite was 0.29- 0.84%RSD and 0.37-1.43% RSD for nitrate, while inter-day precision (n=3) was obtained in the range of 0.20-0.69% RSD for nitrite and 0.31-1.48%RSD for nitrate. The linear range was obtained in the range of 0.05 to 5 mgL-1 for nitrite, and 1 to 50 mgl-1 for nitrate with good linearity (r2 > 0.99). A low detection limit was achieved at 0.05 ± 0.07 mgl1 for nitrite and 0.42 ± 0.04 mgl-1 for nitrate. The accuracy of developed method on analyzing standard sodium nitrite solution of known concentration (0.1 mgl") was 0.75-8.22% relative error and 1.86-7.87% relative error for nitrate (2.5 mgl-1). The developed method was applied for detection nitrite and nitrate in marine water at Chalong Bay, Phuket. Concentration of nitrite was found at 0.06 mgl and nitrate at 0.57 mgL1. The results of developed method were in good agreement with the spectrophotometric method.