A3 Mercury in Water by Vapour Generation AAS Last Revised: May 2015
1. REAGENTS & EQUIPMENT 1.1 Varian AAS with vapour generation accessory 1.2 10 mg/L mercury standard 1.3 Tin (II) chloride (solid) 1.4 Concentrated HCl 1.5 Throsby Creek & bottled water 1.6 0.1% (dilution) and 1% (rinsing) Aristar nitric acid 2. PROCEDURE 2A. Solution preparation 2.1 Determine an appropriate dilution scheme to prepare 5, 10, 20 and 50 ug/L calibration standards from 10 mg/L Hg. Check this with your teacher before proceeding. 2.2 Prepare the standards. All solutions below 1 mg/L must be made up in the 0.1% Aristar nitric acid. 2.3 Weigh tin chloride (4 g) into a 20 mL beaker and add conc. HCl (5 mL). 2.4 Heat gently (DO NOT BOIL) with stirring until dissolved. 2.5 Remove from the heat and allow to cool for a few minutes. 2.6 Pour this solution carefully into a 50 mL beaker containing about 10 mL of ultrapure water. 2.7 Mix well and add enough water to bring up to the 20 mL line. 2B. Analysis 2.8 Set up the instrument for the analysis with the assistance of your teacher. 2.9 Measure the absorbance of ultrapure water, and then the standards in increasing order. 2.10 Run a blank after the top standard to check that the system is flushed. 2.11 Measure the absorbance of the samples: bottled, creek and tap water. 3. REPORT Calculations 1.
Plot a calibration graph for the standards. 2.
Determine the concentration of mercury in the samples. Discussion 
explain the function of the tin chloride 
explain the function of the gas 
compare this technique to electrothermal AAS for the analysis of mercury Questions 1.
What is the Australian Drinking Water Guideline limit for mercury? Do any of the samples fail this? 2.
(a) How does the device described in the Varian article differ from the one used in this exercise? (b) What would be the most significant effect on analytical performance? 3.
(a) What is the most toxic environmental form of mercury? (b) Why wouldn’t it be detected by the method used in this analysis? (c) What modification to the method is required to measure it? (d) How could you determine the concentration of both forms of mercury using cold vapour AAS? 4.
(a) Describe the technique outlined in the Agilent article. (b) What are the two main advantages of the analysis in 4(a) compared to the one used in this exercise. Website resources Australian Drinking Water Guideline Fact Sheet for all pollutants Determination of mercury by cold vapour AAS (Varian) Determination of methyl mercury in water and soil (Agilent) Acknowledgement The preliminary work for this exercise was done by Richard Flew, 2008 Diploma student, as his Practical Project. A3 p2 AI3. HG IN WATER BY VAPOUR GENERATION AAS
RESULTS SHEET
Absorbances Conditions Abs. Blank 5 ug/L 10 ug/L 20 ug/L Bottled water Tap water Creek water