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Applications

Test Se and As Concentration in Wastewater by Using PF7

Introduction
This application note describes the method of testing the concentration of Arsenic and Selenium simultaneously in Wastewater by use of Persee’s Heavy Metal Analyzer (PF7).

Equipment and Reagent
Equipment:
1. Heavy Metal Analyzer with 2 or more lamp slots.
2. As and Se Hollow Cathode Lamp.
3. Hot Plate.

Reagent:
4. HNO3 – HClO4 digestions liquid (50mL HNO3 and 50mL HClO4 mixed together).
5. KBH4 Solution (15g/L): 1.25g KOH dissolved in water, then add 3.75g of KBH4 and dilute to 250mL. This solution must be prepared fresh daily.
6. Thiourea-Ascorbic acid solution: dissolve 1g thiourea in water; add 1g ascorbic acid into the solution. Dilute to 100mL and mix well.
7. HCl solution (5%): 5% HCl dissolved in water.
8. As Standard Solution (20mg/L): transfer 10mL of 100mg/L As solution into 50mL volumetric flask, dilute to 50mL and mix well.
9. Se Standard Solution (5mg/L): transfer 1.00mL of 500mg/L As solution into 100mL volumetric flask, dilute to 100mL and mix well.
10. As and Se Standard Solution (200 g/L As and 50 g/L Se): transfer 1.00mL of As Standard Solution (20mg/L) and 1mL of Se Standard Solution (5mg/L) together into a 100mL volumetric flask, dilute to 100mL and mix well.

Equipment Condition

Instrument Working Parameters:

Table 1. Instrument Working Parameters.

Experiment Procedure
Standard Curve:
Transfer 0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0mL prepared As and Se standard solution (200 g/L As, 50 g/L Se) into 7 different 25mL volumetric flask. Add 2mL HCl (guarantee reagent) solution and mix well. Add 5mL thiourea-ascorbic acid solution. Dilute to the 25mL marker, mix well again. Let solution sit for 30min. Use the prepared KBH4 Solution (15g/L) as Reducer; and HCl solution (5%) as Carrier Liquid. Run the experiment by PF7.

Wastewater Sample Preparation:
Transfer 50mL wastewater sample into a 150mL tall beaker, then add 5mL of HNO3 – HClO4 digestions liquid. Put the tall beaker on a hot plate until white smoke appears around the bottleneck. Remove the beaker from the hotplate and wait for it to cooldown. Add 5mL of HCl (1+1), then continue heating on the hot plate until the yellowish-brown smoke disappears. Remove the beaker from the hotplate and wait for it to cooldown. Transfer the sample into a 25mL volumetric tube with small amount of pure water. Then, add 2mL HCl (guarantee reagent) mix well. Add 5mL thiourea- ascorbic acid solution. Dilute to the 25mL marker, mix well again. Let the solution sit for 30min.

Instrument Procedure:
Use the prepared KBH4 Solution (15g/L) as Reducer; and HCl solution (5%) as Carrier Liquid.

Results
By using the method of HNO3 – HClO4 digestion, interference is limited, thus the result is accurate and reliable. The sensitivity of the experiment is high. The detection limits ofAs and Se are 0.89g/L and 0.5 g/L. The RSD value of the mixed standard solution (24 g/L As and 6 g/L Se) are 3.5% and 1. 1% and the Recovery rates are 91.5%~101.2% and 94%~100.5% for As and Se respectively.

As Results by PF7:
Standard Curve:

As Standard Graph at 10 g/L:

As Quality Control 1:

As Quality Control 2:

As Sample 1:

As Sample 2:

As Final Results:

Se Results by PF7:
Standard Curve:

Se Standard Graph at 10 g/L:

Se Sample 1:

Se Sample 2:

Se Final Results:

 

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