Hydride Generation——Atomic Absorption Spectrometry for Determination of Arsenic in Soil

Abstract Through the experimental determination and specific analysis, it is considered that hydride generation-atomic absorption method for the determination of arsenic in soil has the advantages of high accuracy, good precision, fast analysis speed, simple method, economical and practical, etc. An effective method.
Key words soil; arsenic; analytical method arsenic is one of the toxic and harmful elements in the soil. If its content exceeds the standard, it is extremely harmful to the human body. Therefore, the determination of arsenic in soil is very important. The analysis of arsenic is commonly carried out by silver salt method, colorimetric method and spectrophotometry. Because some traditional methods are cumbersome, the analysis time is long and the measurement results are unstable. Therefore, we have used hydride generation-atomic absorption method to determine the content of arsenic. This method has the characteristics of high sensitivity, high precision, high reliability and convenient operation.

1 Test part 1.1 Main instruments and reagents (1) AA220 type atomic absorption spectrophotometer, KJ-08W type flow injection hydride generator.
(2) Primary reagents. Arsenic standard solution (500ug/mL), hydrochloric acid (excellent grade), nitric acid (excellent grade), potassium dichromate (excellent grade), thiourea, ascorbic acid, potassium borohydride, potassium iodide. Different concentrations of solution were prepared as needed.

1.2 Test procedure 1.2.1 Sample pretreatment. The sample used in this test is the standard material GBW07408 (produced by the Geophysical and Geochemical Investigation Institute). Weigh the sample m=0.1000g and place it in a 25mL colorimetric tube. Add 5mL of (1+1) aqua regia, shake it up, and dilute it overnight. The next day, the mixture was heated and dissolved in a boiling water bath for 2 hours, and taken out for cooling. Add 5 mL of 5% thiourea + 5% ascorbic acid solution, dilute to the mark with 2% potassium dichromate solution, shake well, and let stand. Take the supernatant diluted 10 times to be tested.
A blank solution was prepared in the same procedure for blank correction of the sample solution.
1.2.2 Determination conditions. The instrument measurement conditions and hydride generation conditions are shown in Tables 1 and 2.
1.2.3 Determination. The standard mother liquor was prepared by stepwise dilution with 500 ug/mL arsenic standard solution and reduced to 1 ug/mL AsIII. The standard series of arsenic was prepared using this solution. 0.0 mL, 0.2 mL, 0.4 mL, 0.6 mL, and 0.8 mL of a standard mother liquid were added to five 100 mL volumetric flasks, and dissolved in 100 mL with a 10% hydrochloric acid solution. This is a series of standard solutions of 0.00 ng/mL, 2.00 ng/mL, 4.00 ng/mL, 6.00 ng/mL, and 8.00 ng/mL. The working curve is shown in Fig. 1. The correlation coefficient is r=0.9994. The abscissa concentration value and the ordinate absorbance value can be read from the instrument (see Table 3). After the working curve is established, the blank solution and the sample solution are separately injected, and the concentration value can also be read on the instrument (see Table 4).

2 Results and discussion 2.1 As-state valence reduction Aspirate 1 mL of As standard solution with a concentration of 100 ug/mL into a 100 mL volumetric flask, add 0.8 g of potassium iodide, dissolve to 100 mL with 10% hydrochloric acid solution, and pour into a beaker. The furnace was heated to a slight boiling, allowed to cool, and 0.5 g of ascorbic acid was added. The standard solution is a standard mother liquor of 1 ug/mL AsIII, which is sealed in a brown bottle and protected from light. When used again, it does not need to be validated and can be used for half a year.

2.2 Use of potassium borohydride solution The potassium borohydride solution should be stored in a polyethylene plastic bottle. It is used now. If the storage time is too long, the reducing power will decrease, and the detection sensitivity will decrease. The shelf life is 7d.

2.3 The preparation of arsenic standard solution is different due to different atomic absorption models, and the sensitivity is also different. Therefore, when making arsenic series standard solution, it should be prepared according to the specific conditions. In short, the large reading of zui should not exceed 0.8A, otherwise the concentration is too high. Will cause the curve to bend, the small reading of Zui is greater than 0.02A (the reading after subtracting the blank).

2.4 Determination of the effect of the conditions on the results 2.4.1 room temperature. The low room temperature of zui should be above 15 °C, and the sensitivity is higher at room temperature, and vice versa.
2.4.2 Carrier gas flow rate. It can be preferably between 120 and 180 mL/min, and the sample and working curve must be determined under the same conditions.
2.4.3 Acidity. The acidity of the sample is very important. If the acidity does not match, it will have a great influence on the sensitivity and stability. Therefore, the acidity of the sample should be consistent with the standard working curve.
2.4.4 Vessels. Colorimetric tubes, volumetric flasks, pipettes, etc., which can cause contamination, are soaked in 1:1 nitric acid overnight, washed and rinsed with deionized water for 3 times, and dried for use.

2.5 Results Calculate the solution volume V=25.0mL, the dilution factor N=10, and then calculate the sample content according to the concentration value C of Table 4. Formula X (mg/kg)=(CC blank)×V×N/m (note unit Conversion). The substitution values ​​obtained by substituting the formula were X1 = 12.0 mg/kg, X2 = 11.9 mg/kg, X3 = 11.8 mg/kg, and X4 = 12.2 mg/kg, respectively. See Table 5 for precision and accuracy.

2.6 Conclusion Through the analysis of GBW07408 soil standard, it can be seen that the value measured by this method is within the allowable error range and is consistent with the actual value. We believe that hydride generation-atomic absorption method for the determination of arsenic in soil has the advantages of high accuracy, good precision, fast analysis, simple method, economical and practical, etc., as long as the operation steps are strictly followed to keep the generator free from pollution. , can quickly complete the task, is an effective method to detect arsenic in the soil.

This article is derived from hydride generation-atomic absorption method for the determination of arsenic in soil | Science Instruments Online Original link: /knowledgeview2446

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