Proper handling of water samples is crucial for maintaining their integrity and ensuring accurate analytical results, involving careful preparation, filling, storage, and timely analysis.
Effective water sample handling follows a structured approach to prevent contamination and degradation, ensuring the reliability of laboratory analysis. The process begins right at the sampling site and extends through transportation to the laboratory.
Bottle Preparation and Rinsing
Before collecting the actual sample, preparing the collection bottles correctly is a fundamental step.
- Rinse the bottles thoroughly with the sample water itself. This pre-rinse helps to condition the bottle to the water's properties and removes any residual contaminants from the bottle's previous use or manufacturing process that could otherwise affect the sample's composition.
Sample Collection and Filling
The method of filling the sample bottle significantly impacts the sample's stability and integrity, particularly for sensitive parameters.
- Once rinsed, fill the bottles completely to the brim. This practice minimizes the air space above the sample, reducing the potential for gas exchange between the sample and the atmosphere, which can alter concentrations of dissolved gases or volatile compounds.
Special Considerations for Oxygen and pH Samples
- For samples designated for oxygen (O2) and pH analysis, it is critically important to ensure no air bubbles are allowed on the walls of the bottle or within the sample itself. Air bubbles can introduce atmospheric oxygen, artificially increasing the dissolved oxygen content, and potentially altering the pH through carbon dioxide exchange. Careful filling techniques, such as slowly pouring the water down the side of the bottle, can help prevent bubble formation.
Storage and Transportation
The conditions under which samples are stored and transported are vital to prevent degradation and maintain their original characteristics.
- During transport to the laboratory and while awaiting analysis in the lab, store the bottles in a cool and dark environment. This helps to inhibit biological activity (e.g., microbial growth), prevent undesirable chemical reactions (e.g., oxidation), and reduce the degradation of sensitive compounds that are susceptible to light or heat. Using coolers with ice packs and opaque containers is recommended.
Timely Analysis
The time elapsed between sampling and analysis is a critical factor influencing result accuracy.
- To ensure the most representative and accurate results, perform the analysis as soon as possible after sampling. The longer a sample is stored, the higher the likelihood of chemical or biological changes occurring within the sample, which can lead to inaccurate or misleading data. Adhering to recommended holding times for specific parameters is essential.
Summary of Water Sample Handling Guidelines
| Stage | Key Action | Purpose |
|---|---|---|
| Bottle Preparation | Rinse with sample water | Conditions bottle, removes potential contaminants. |
| Sample Filling | Fill to the brim | Minimizes air space, reduces gas exchange and oxidation. |
| Specific Samples | No air bubbles for O2 & pH | Prevents atmospheric O2 introduction, maintains accurate readings. |
| Storage/Transport | Store cool and dark | Inhibits biological activity, prevents chemical degradation. |
| Analysis | Perform as soon as possible | Ensures accurate results, minimizes changes in sample composition. |
