One-time standard colour references analysis of hexavalent chromium by 1,5-diphenylcarbazide in environmental water matrices using camera-based approach

Abstract

ABSTRACT The analysis of hexavalent chromium (Cr (VI)) is an important water quality monitoring for public health safe consumption. Many high-end instruments were accessible to detect total Cr precisely at parts per trillion. Because of high upkeep of instruments, important to recognise on field examination and adjusting to low-volume (green chemistry) was quite challenging. The potential methods of detecting Cr in on-spot field examination were colorimetry. Numerous scientists were carried out by lab or compact spectrophotometer using 1,5-diphenylcarbazide and ability to produce magenta at 540 nm absorbance. The detection limit was achieved as per the WHO regulation levels. Still the requirement of standardisation in the field analysis was not completely suitable for low-volume due to use of standard chemicals. So in our study, the regular method was evaluated with the colour science approach by uniform (Lab, HLab and XYZ) and non-uniform models (RGB) with spectrophotometer and different cameras (mobile and digital still) using its flash light. The study showed Cr (VI) analysis by mobile camera was able to detect at 20 ng/mL. This was far better than recent reported studies with microfluidic and nanotechnology. The analytical relation with ICP-MS and mobile for Cr (VI) was found to be 0.60 (RSE-6.2%) to 0.72 (RSE-6.72%) with adjusted r2 value > 0.98. We have found to be in good agreement of ~70% with 98% confidence level of uniform models than non-uniform. The use of one-time colour standard references of uniform models might be helpful through naked eye judgment and ability to detect at 100 ng/mL based on individual perceptions in field analysis. This will improve in determining the sample collection, site evaluation for remediation and involvement of public in the water monitoring programmes. Further studies have to be conducted in tuning models to detect as precisely like high-end instruments using various NIST SRM standards.