V4
ANODIC STRIPPING VOLTAMMETRY
Last Revised: August 2014 1. PURPOSE This exercise determines the concentration of heavy metals in water samples by anodic stripping voltammetry (ASV), and investigates one of the options for improving sensitivity. 2. REAGENTS & EQUIPMENT 2.1 Metrohm polarograph 2.2 1 & 5 mg/L Pb standards 2.3 1% Aristar nitric acid (glassware rinsing) 2.4 4% ethanoic acid (leaching) 2.5 pH 4.6 ethanoate buffer 2.6 Dosimat standard (5 mg/L Cu & Zn, 500 ug/L Pb, 50 ug/L Cd) 2.7 Lead crystal drinking glass 2.8 Leach solution, 24 hour contact with lead crystal 3. PROCEDURE 3A. Solution preparation 3.1 Almost fill the lead crystal drinking glass with 4% ethanoic acid. Cover with plastic film and leave for 30 minutes. Transfer to a rinsed plastic container. 3.2 Rinse ALL glassware to be used with 1% Aristar nitric acid. 3.3 Prepare 100 mL of a 50 ug/L Pb standard from the 1 mg/L Pb solution provided. 3B. Variation in deposition time 3.4 Add 10 mL (measuring cylinder) of the 50 ug/L Pb standard into the acid‐rinsed cell, and add 1 mL (this can be done each time by plastic Pasteur pipette) of the ethanoate buffer solution. 3.5 Load the method V4 DepTime. 3.6 Follow the instructions provided on the separate sheet. 3.7 Record the peak height (current). 3.8 Re‐run the solution with deposition times of 120 and 300 seconds. Remember that you don’t have to do the purge for these two runs. 3C. Analysis 3.9 Pipette 10 mL of tap water and 1 mL of the ethanoate buffer into the sample cell. 3.10 Load the method V4 CuPbCdZn. The standard additions are done using the Dosimat delivery system – the software will prompt you to make the addition of 0.2 mL. 3.11 Load the method V4 Leach. 3.12 Pipette 10 mL of the 30 minute leach solution into the cell and 1 mL of the ethanoate buffer and run the analysis. The standard additions are manual – 100 uL of the 5 mg/L standard by micropipette. 3.13 Repeat step 3.12 with the 24 hour solution. 4. REPORT Calculations The computer interface should do the standard addition calculations for you for the four metals in tap water. However, there are occasions where problems with the measurements mean that you will have to do the calculations yourself. The calculations have been disabled for the Leaching analysis. You are required to do these yourself. Note that the ethanoic acid leaching solution has been analysed and found to contain 82 ng Pb/10 mL. 
plot a graph showing the difference in current for the three different stripping times 
determine the concentrations of the metals in ug/L in the tap water and the leachate from the lead crystal glass 
calculate the mass of lead in 150 mL of the 30 minute leach solution (equivalent to one glass of wine) 
calculate the mass of lead in 50 mL of the 24 hour minute leach solution (equivalent to one glass of whisky) Discussion 
explain the reasons for the choice of (a) deposition voltage and (c) scan range for the two analyses 
explain why ASV has a better sensitivity than differential pulse polarography 
explain why multiple runs can be conducted on the same solution 
comment on the difference in response for the different deposition times 
discuss how varying the deposition time can be employed for solutions of different concentration levels Questions 1. What are the accepted levels of the four analytes in drinking water in Australia? How do your results compare with these standards? 2.
The recommended maximum daily intake of lead is 4 ug/kg of body weight. What percentage of this would be provided by the glass of (a) “wine” and (b) “whisky” from the calculations? Assume an average adult body weight of 75 kg. 3.
Read the Metrohm method for analysis of cadmium, lead and copper in wine (V‐93) provided. What sample preparation step is used? Explain why this would be necessary. V4 p2 V4. ANODIC STRIPPING VOLTAMMETRY RESULTS SHEET 3B. Deposition time Time (s) Current 60 120 300 3C. Metals in tap water You only need to record these if there is a problem with some of the readings. Cu Pb Cd Zn Sample Addition 1 Addition 2 Addition 3 3C. Lead leaching 30 mins 24 hours Sample Addition 1 Addition 2 Addition 3