What is a preservative, and why is it important? According to the EPA, methods of preservation are relatively limited and are intended generally to (1) retard biological action, (2) retard hydrolysis of chemical compounds and complexes, (3) reduce volatility of constituents, and (4) reduce absorption effects.
In other words, the purpose of a preservative is to “freeze” the sample chemistry at the point of sampling so that what gets analyzed at the lab is as similar to the source as possible, despite the unavoidable delay between the sampling and analysis.
Some common preservatives include:
- Sulfuric Acid (H2SO4)
- Preservative for Nutrients: Total Nitrogen, Ammonia, Phosphorus, TKN, etc.
- Nitric Acid (HNO3)
- Preservative for Metals: Arsenic, Sodium, Lead, Copper, Iron, Mercury, etc.
- Sodium Thiosulfate (Na2S2O3)
- Preservative for Bacteria: Total Coliform, E. Coli, Fecal
- Sodium Hydroxide (NaOH)
- Preservative for Cyanide: Total CN, Free CN, WAD CN, etc.
- Hydrochloric Acid (HCl) in VOA vials
- Preservative for Volatile Organics: VOCs and Gasoline
- Hydrochloric Acid (HCl) in Amber Glass
- Preservative for Organics: Oil & Grease, Diesel, Oil, etc.
However, the most important, but often overlooked, preservative is ice. Keeping a sample cold (between 2-6C) is a requirement for nearly every analytical test we perform EXCEPT for metals analysis. It is generally preferable to use wet ice instead of ice packs when possible.
Sample containers, just like preservatives, are designed to inhibit the natural chemical changes which will occur in a sample as time passes. In addition to that, sample containers also serve a few other purposes:
- To ensure proper volume is provided to a lab (all tests have a minimum required volume)
- To ensure the lab has enough volume to perform the proper quality control
- Some containers limit a samples exposure to UV rays
- Some containers are designed to prevent sample contact with air
- Some are sterilized and sealed to prevent bacteria contamination
- Some containers are designed to limit sample absorption (plastic vs. glass)
- Some are specifically designed to be loaded directly into an instrument (or even an autosampler for composite samples)
But how do I know which sample bottle and preservative to use? Simple, you ask the lab! By contacting WETLAB before you begin your sampling process, you will help ensure that you use the correct bottle and preservative. Our staff can also help you review your permit making sure the correct samples are taken at the correct time of the year (DPBs, LCR, SOCs), and making sure the correct methods are used for your sample matrix (drinking water, waste water, haz waste). We can even help with sampling requirements making sure your samples are collected as intended by your permit (LCR first draw, grab vs. composite), saving you valuable time that can be lost from unintended mistakes.
Be aware, preservatives and hold times are dictated by the analytical method and enforced by state/federal agencies and the laboratory. Cyanide species, Volatile Organics, Dissolved Oxygen, Bacteria, SOCs, DBPs, and many other tests absolutely require correct bottles and preservatives to analyze for compliance.
Contact WETLAB at (775)355-0202 to discuss your sampling needs. Our seasoned staff can help you determine which samples you need, how they need to be collected, and provide you with all the right bottles and preservatives to make sure your procedures remain in compliance.