Description
Among the various HgII sensing approaches, paper-based sensors are widely used to provide low cost and simple means of on-site analysis. The advantage of using paper is well documented. Paper-based sensors are manually cut into strips or sections and soaking in chemical reagent(s) that change colour on exposure to a specific pollutant; the change in colour relates to the pollutant concentration and can be estimated by the naked eye or read out by an electronic device.In this work, three different chromogenic reagents for the detection of Hg were selected: cuprous iodide (Cu2I2), diphenylcarbazone (DPC) and rhodamine 6G (R6G), and their analytical performance compared when used in spot test mode (both as wet reagents and when dried onto filter papers), and in the apparatus recommended by Yallouz et al.1 for semi-quantitative Hg screening in environmental sample. In the spot test, DPC and R6G test papers were produced by immersing filter papers in 1% DPC in ethanol and in a mixture of 1 mL hexamine buffer, 2.5 mL 10% potassium iodide, 5 mL 0.01% R6G and 1 ml 1% gelatin, respectively. Approximately 100 µL of Hg standard solutions was dropped onto the surface of the test paper immediately after the papers were produced, and after they had been completely dried under ambient condition.
Visual detection by the reaction between HgII and Cu2I2, DPC and R6G was observed. The Cu2I2 detecting papers were not considered suitable for use in spot test mode as a result of colour bleaching of the paper upon the addition of Hg standard solutions. In the semi-quantitative screening method, the intensity of the coloured complex Cu2[HgI4] produced on the detecting papers increased with increasing Hg concentration in the standards. The Hg-DPC compound formed with the coordination of DPC with Hg was suitable for colorimetric determination of Hg in wet paper condition. The intensity of purple coloured complex obtained increased as the concentrations of Hg in the standards increase. However, because of the oxidation of the DPC on the dried test papers, this reagent could not be adapted to the Hg semi-quantitative screening method. The reaction between [HgI4]2- and R6G was successfully achieved by producing an ion-associate [(HgI4)2-[(R6G)+]2 that has a characteristic pink colour both in wet and dry spot test mode. However, leaching of R6G was observed upon addition of Hg standards under dry papers condition. The performance using the semi-quantitative screening method was achieved. The absorbance spectra of Hg-complexes were measured directly on the surface of detecting papers using UV-vis reflectance spectroscopy. Linear calibration between the absorbance and Hg concentrations was obtained with a strong correlation coefficient of r2=0.9726 and r2=0.9238 for Cu2[HgI4] and [(HgI4)2-[(R6G)+]2, respectively.
1. A. V. Yallouz, R. G. Cesar and S. G. Egler, Environmental Pollution, 2008, 151, 429-433.
| Period | 14 Dec 2016 |
|---|---|
| Event title | 9th Scottish Symposium on Environmental Analytical Chemistry |
| Event type | Conference |
| Location | Dundee, United KingdomShow on map |
| Degree of Recognition | Regional |