Background:
Sarin is a nerve agent which is lethal to people due to its high toxicity. According
to its extreme toxicity, sarin, relatively lack of color, highly toxic, miscible in water, poses
viable threats to potable water sources. Therefore, there is an urgent need for portable, rapid and yet
reliable methods to monitor for adulteration of potable water sources by sarin on spot.
Methods:
A stock solution of 30 mg/L sarin was prepared daily by dissolving 300 μg of sarin in
10 mL isopropanol. A certain amount of sarin was added to the glass tube, and then o-dianisidine and
hydrogen peroxide were added. The pH value of the solution was adjusted to 9.8. The solution was
transferred to the test tube after 10 minutes. A test tube of 2 mL was placed between the light source
and the RGB color sensor. The LED light source illuminates directly over the test tube while the
RGB sensor obtained the generated spectral response. This RGB voltage output is connected to the
ADC and microcontroller to convert these analog voltages to three digital data. This RGB digital data
is linked to the microcomputer through the serial port that is interfaced with the user interface. The
data thus obtained in the sensor can be processed to display the sarin concentration.
Results:
Under the optimum conditions as described above, the calibration curve of chromaticity
value versus sarin concentration was linear in the range of 0.15 mg/L to 7.8 mg/L. According to the
IUPAC definition, theoretical detection limits of this method were 0.147 mg/L and 0.140 mg/L for R
and B values, respectively. The practical detection limit was 0.15 mg/L. The sensor was successfully
applied to the determination of sarin in artificial water samples and the recoveries were between
86.0% to 95.9%.
Conclusion:
The results in the present work have demonstrated the feasibility to design a new portable
colorimetric sensor based on the RGB chromaticity method for quantitative determination of sarin
in water. The influences of chromogenic reagent, oxidant, reaction time, o-dianisidine concentration,
hydrogen peroxide concentration, reaction temperature, pH on the chromaticity values were investigated.
The results showed that the sensor possessed high selectivity, sensitivity and good repeatability.
The method would be potentially applied to the analysis of other toxic compounds in
environment, such as other chemical warfare agents.
Spectrometric Determination of Heavy Metals Present in Mango Fruit of Nepali Origin
