Part 8: Preparing Solutions
This section describes the routine solutions needed for total arsenic measurements.
This section describes the routine solutions needed for total arsenic measurements. Once prepared, these solutions can normally be used for many measurement sessions if stored correctly and labelled clearly.
Always add acid to water, never water to acid. Wear safety glasses, gloves and protective clothing. Prepare acids in a fume hood where possible.
0.5 M sulfuric acid for electrode conditioning
Sulfuric acid is used to clean and activate the electrode surface before arsenic measurements.
| Component | Amount for 100 mL |
|---|---|
| Deionized water | Start with approximately 80 mL |
| Concentrated H2SO4, 98% | 2.72 mL |
| Final volume | Make up to 100 mL with DI water |
Label: 0.5 M H2SO4 - for electrode conditioning. Store at room temperature unless local procedures specify otherwise.
1 M hydrochloric acid for measurement electrolyte
Hydrochloric acid is used to prepare the measurement electrolyte and acidify samples.
| Component | Amount for 100 mL |
|---|---|
| Deionized water | Start with approximately 80 mL |
| Concentrated HCl, 36% | 8.1 mL |
| Final volume | Make up to 100 mL with DI water |
If your concentrated HCl is 32%, use approximately 9.8 mL instead. Label and store at room temperature.
1ppm Arsenic standard solution
For most users, purchasing certified arsenic standard solutions is strongly recommended. This avoids handling solid arsenic compounds and reduces safety and waste-disposal requirements. The standard is used during standard addition measurements to calculate the unknown arsenic concentration in the sample.
Use a certified aqueous arsenic standard whenever possible. Store standards in clearly labelled containers with date, concentration, and hazard warnings.