Rapid assessment of soil accessible Cr(â ¥) in the field by a portable RGB color sensor.

Field rapid determination of soil accessible Cr(Ⅵ) is of great significance for on-site assessment and decision-making about the health risks of contaminated sites. When the thickness of solutions with various concentrations of Cr(Ⅵ) is constant, there would be a quantitative relationship between the chromogenic difference of Cr(Ⅵ) solutions and the concentration of Cr(Ⅵ). The chromogenic difference could be described by Red (R), Green (G), Blue (B) values. Based on the chromogenic reaction between 1,5-diphenylcarbazide and Cr(Ⅵ), this study first established the calibration curve between the chromogenic difference and the concentration of Cr(Ⅵ) in standard solution with or without 0.01 M CaCl2, using an RGB color sensor. This is the subsequent determination basis of the method for rapidly assessing accessible Cr(Ⅵ) in the field (M-RGB). Then, the concentration of accessible Cr(Ⅵ) of contaminated soil with "hand-shaking + standing" field extraction method was compared with "end-over-end shaking" laboratory extraction method. Finally, the accessible Cr(Ⅵ) of contaminated soil extractants was determined via M-RGB integrating the field extraction method. Results indicated there was a highly significant linear relationship between colorimetric difference value (∆E) and Cr(Ⅵ) concentration in the range of 0.1-3 mg/L (R2 > 0.99, P < 0.01), based on the Euclidean formula for calculating ∆E. The "hand-shaking + standing" field extraction method was effective in obtaining accessible Cr(Ⅵ) extractants with or without 0.01 M CaCl2, with the high extraction efficiency within 100±1%. The concentrations of accessible Cr(Ⅵ) in various polluted soils determined by M-RGB were consistent with that determined by the ultraviolet-visible spectrophotometry, with the relative error within ±5%, and the relative standard deviation ≤ 20%. The spiked recovery experiments showed that the recovery of M-RGB was between 95% and 105%, which means M-RGB could realize the trace analysis for accessible Cr(Ⅵ) in the field.

Using an inexpensive RGB color sensor for field quantitative assessment of soil accessible Cu(â ¡).

Field rapid determination of soil accessible Cu(Ⅱ) was important for environmental safety and human health risk assessment. In this study, an inexpensive red, green, and blue (RGB) color sensor was used for quantitative color difference analysis of the colored solution for soil accessible Cu(Ⅱ) with bis-cyclohexanone oxalydihydrazone as color reagent to develop a new method for analyzing soil accessible under field conditions. First, the calibration curve for RGB color sensor method was established in the standard solutions of Cu(II). Then the "hand shaking + standing" field extraction method for accessible Cu(Ⅱ) was developed. Finally, the method was applied in contaminated soils in the laboratory and in the field, and set the values determined by atomic absorption spectroscopy (AAS) as the standard ones. Results indicated that in the range of 0.1-5 mg L-1 Cu(II), the RGB Euclidean chromogenic difference values were directly linear correlated with the concentration of Cu(II) (R2 > 0.999). The interference of Fe(Ⅲ) and Mn(Ⅱ) could be eliminated by adding citric acid. The "hand shaking + standing" field extraction method could effectively extract the accessible Cu(Ⅱ) from soil with the high extraction rates. The concentrations of accessible Cu(II) in various polluted soils determined by RGB color sensor method were consistent with that determined by AAS, with the relative error within ±5%, the relative standard deviation ≤ 20%. The recovery of Cu(II) in RGB color sensor method was between 97% and 105%, which could meet the requirements of trace analysis of accessible Cu(Ⅱ) in the field. The high accuracy and precision of RGB color sensor method was reconfirmed in the rapid field quantitative assessment of soil accessible Cu(Ⅱ). Due to that the RGB color sensor was low cost, rechargeable, portable, mobile, ambient light resistant, the method would have a great potential for the determination of accessible Cu(Ⅱ) in contaminated soils.