Determination of Zinc, Cadmium, Lead and Copper in Effluent Sample

Transcription

1 Determination of Zinc, Cadmium, Lead and Copper in Effluent Sample Branch: General analytical chemistry, water, waste water, environmental protection Key Words 797 / polarography / VA / 8 / Zn / Cd / Pb / / HMDE / effluent / branch 1, 2 Summary To determine the levels of zinc, cadmium, lead and copper in effluent sample using voltammetry. Sample Effluent sample containing around 3 mg/l of organics Apparatus and accessories 797 VA Computrace 8 Dosinos Electrodes WE MME AE Pt RE Ag/AgCl/KCl (3 mol/l) Reagents Nitric acid Zn standard stock solution, β[zn(ii)] = 1 g/l Cd standard stock solution, β[cd(ii)] = 1 g/l Pb standard stock solution, β[pb(ii)] = 1 g/l standard stock solution, β[(ii)] = 1 g/l Ready-to-use solutions: Acetate buffer Standard addition solution 56.9 g potassium chloride and 2.5 g sodium acetate were added to 25 ml deionised water in 5 ml volumetric flask. Make up to mark with deionised water. 1 mg/l Zn, 4 mg /L Cd, 4 mg/l Pb and 1 mg/l To each cuvette was added 2 µl of H 2O 2 to aid the photolytic generation of OH radicals along with 1 µl of HCl (3%) to acidify the solutions to ph 2. The samples were digested at 9ºC for a period of 12 minutes. After 1 hour a further 1 µl of H 2O 2 was added. A blank sample was also digested (i.e. 1 ml of UPW plus H 2O 2 and HCl). Analysis 2 ml of sample, 7.5 ml upw and 2 ml acetate buffer (from Dosino) were added to the reaction vessel. The concentration was then determined using two standard additions of 4 µl with the HMDE using the 8 Dosino. Voltammetric parameters working electrode drop size 1 stirrer speed mode initial purge time addition purge time deposition deposition potential deposition time sweep equilibration time pulse amplitude start potential end potential voltage step voltage step time sweep rate peak potential Zn peak potential Cd peak potential Pb peak potential HMDE 2 rpm DP 3 s 3 s -115 mv 3 mv 15 s 5 mv -115 mv 2 mv 6 mv.1 s 6 mv/s -98 mv -56 mv -38 mv -1 mv Sample Preparation 5 ml of sample was added to 5 ml of ultra pure water (Milli Q Advantage) in each of the quartz cuvettes of the UV digestor.

2 Page 2/7 Example Determination of Zinc, Cadmium, Lead, and Copper acc. to DIN3846/16 Zn sample 1 2n c =.21 mg/l +/-.3 mg/l (14.8%) 8.n 6.n 15n 4.n 1n 5.n Cd Pb U (V) Zn c =.114 mg/l +/-.4 mg/l (3.64%) 5.n 4.n 3.n 2.n 1.n 2n 15n 1n 5.n -9.9e-6-2.e-5 2.e-5 4.e-5 6.e-5 Cd c = e-6 1.e-5 1.5e-5 2.e-5 2.5e-5 Pb c =.46 mg/l +/-.4 mg/l (8.66%) 3.n Results 2.n -1.8e-6 Sample ID 2.e-5 4.e-5 6.e-5 Zn Cd Pb µg/l µg/l µg/l µg/l blank corrected corrected Comments The sample requires UV digestion because of the high levels or organics that would otherwise interfere with the electrochemical signal. A blank is essential when working at low levels at Metrohm UK because the applications laboratory is not trace level specific and also utilized for other metal analysis at higher concentrations (e.g. titration). From the method used it may be concluded that voltammetry with UV digestion can be used to determine the levels of zinc, cadmium, lead and copper in effluent sample. Date 7 December 27 2.n 1.n Name Jonathan Bruce BSc MRSC -4e-6 1.e-5 2.e-5 3.e-5

3 Page 3/7 Full report of example ===== METROHM 797 VA COMPUTRACE (Version ) (Serial No. 1135)======== Determination : _sample 1.dth Sample ID : sample 1 Creator method : Date : Time: 14:38:15 Creator determ.: Date : Time: 15:38:44 Modified by : Date : Time: 14:29:5 Method : BSF_AB231_1.mth Title : Determination of Zinc, Cadmium, Lead, and Copper acc. to DIN3846/16 Remark1 : 2 ml acetate buffer Remark2 : 7.5ml upw + 2ml sample Sample amount : 2. ml Cell volume : 11.5 ml Substance : Zn Conc. : ug/l Conc.dev. :.362 ug/l ( 3.64%) Amount : ng Add.amount : 4. ng Substance : Cd Conc. : --- Conc.dev. : --- Add.amount : 16. ng No peak found No peak found Substance : Pb Conc. : ug/l Conc.dev. :.346 ug/l ( 8.66%) Amount : ng Add.amount : 16. ng

4 Page 4/ Substance : Conc. : ug/l Conc.dev. :.256 ug/l (14.8%) Amount : 2.94 ng Add.amount : 4. ng Substance Calibr. Y.reg/offset Slope Mean deviat. Corr.Coeff Zn std.add e e e Cd std.add e e e Pb std.add. 4.88e e e std.add e e e Solutions No. Content Predose (ml) Buffer electrolyte 2. 2 Mixed standard Final results +/- Res. dev. % Comments Zn: Zinc =.114 mg/l Cd: Cadmium = --- ug/l No result found Pb: Lead =.46 mg/l : Copper =.21 mg/l Electrode Test : passed

5 Page 5/7 Method Print Method parameters Method : BSF_AB231_1.mth Title : Determination of Zinc, Cadmium, Lead, and Copper acc. to DIN3846/16 Remark1 : 2 ml acetate buffer Remark2 : 7.5ml upw + 2ml sample Calibration Technique Addition : Standard addition : Batch : Automatic Sample ID : sample 1 Sample amount (ml): 2. Cell volume (ml): 11.5 Voltammetric parameters Mode : DP - Differential Pulse Highest current range Lowest current range : 1 ma : 1 na Electrode : HMDE Drop size (1..9) : 2 Stirrer speed (rpm) : 2 Initial electr. conditioning : No No. of additions : 2 No. of replications : 2 Measure blank : No Addition purge time (s) : 3 Initial purge time (s) : 3 Conditioning cycles Start potential (V) :. End potential (V) :. No. of cycles : Hydrodynamic (measurement) : No Cleaning potential (V) :. Cleaning time (s) :. Deposition potential (V) : Deposition time (s) : 3. Sweep Equilibration time (s) : 15. Start potential (V) : End potential (V) :.25 Voltage step (V) :.6 Voltage step time (s) :.1 Sweep rate (V/s) :.6 Pulse amplitude (V) :.5 Pulse time (s) :.4

6 Page 6/7 Cell off after measurement : Yes Peak evaluation Regression technique : Linear Regression Peak evaluation : Height Minimum peak width (V.steps) : 1 Minimum peak height (A) : 1.e-1 Reverse peaks : No Smooth factor : 4 Eliminate spikes : Yes Substances Zn : -.98 V +/-.1 V Standard solution : 2 1. mg/l Addition volume (ml) :.4 Zinc : Final result (Zn) = Conc * (11.5 / 2) * (2 / 1) + - Cd : -.56 V +/-.1 V Standard solution : 2 4. mg/l Addition volume (ml) :.4 Cadmium : Final result (Cd) = Conc * (11.5 / 2) * (2e+6 / 1) + - Pb : -.38 V +/-.1 V Standard solution : 2 4. mg/l Addition volume (ml) :.4 Lead : Final result (Pb) = Conc * (11.5 / 2) * (2 / 1) + - : -.1 V +/-.1 V Standard solution : 2 1. mg/l Addition volume (ml) :.4 Copper : Final result () = Conc * (11.5 / 2) * (2 / 1) + - Baseline Substance Addition automatic start (V) end (V) type scope Zn Sample yes linear wholepeak Addition 1 yes linear wholepeak Cd Sample yes linear wholepeak Addition 1 yes linear wholepeak Pb Sample yes linear wholepeak

7 Page 7/7 Addition 1 yes linear wholepeak --- Sample yes linear wholepeak Addition 1 no linear wholepeak Solutions No. Content Predose (ml) Buffer electrolyte 2. 2 Mixed standard