Ultrapure Water Applications – Cleaning Guidelines for Containers Holding Water Samples

The method for cleaning containers should be determined according to the requirements of the water sample testing project.

1. Samples for general chemical analysis

When analyzing trace chemical components in surface water or wastewater, thoroughly cleaned new containers are usually used to reduce the possibility of recontamination. The general cleaning procedure is to wash with water and detergent, then with lead-acid-sulfuric acid solution, and finally rinse thoroughly with tap water or distilled water. The type of detergent and the material of the container should be determined according to the analyte. Phosphate-containing detergents cannot be used for phosphate determination; chromic acid-sulfuric acid solution cannot be used for sulfate or chromium determination. Glass containers and polyethylene containers for heavy metal determination are usually cleaned with hydrochloric acid or nitric acid (C = 1 mol/L) and soaked for one to two days, then rinsed with distilled water or deionized water.

1.2 Samples for determining pesticides, herbicides, etc.

Amber glass bottles are generally used. Because plastic containers other than polytetrafluoroethylene (PTFT) can significantly interfere with the analysis, they should be cleaned according to general procedures (i.e., water and detergent – chromic acid – sulfuric acid cleaning solution – distilled water), and then dried in an oven at 180°C for 4 hours. After cooling, rinse several times with purified hexane or petroleum ether.

1.3 Samples for Microbiological Analysis

Containers, stoppers, and lids should be sterilized at a temperature that does not release or produce any chemicals that inhibit biological activity, inactivate, or promote biological growth.

Glass containers should be washed according to general cleaning principles, soaked in nitric acid, and then rinsed with distilled water to remove heavy metal or chromate residues.

Before sterilization, sodium thiosulfate (Na₂S₂O₃) can be added to the container to remove the inhibitory effect of residual chlorine on bacteria. (The dosage is 0.1 mL of 10% Na₂S₂O₃ per 125 mL container.)