Editorial Article: Webinar Highlights: The Forgotten Variable: Laboratory Water Purity and its Impact on Your Experiments

Your questions answered on using ultrapure water for analytical experiments and how to avoid the effects of contaminants

14 Jul 2017

Dr. Estelle Riche, Merck KGaA, Darmstadt, Germany


The quality of your laboratory water has a large influence on the quality of results obtained in research. In a recent SelectScience® webinar, Dr. Estelle Riche, Senior Application Scientist from Millipore SAS, highlights the potential impact of water contaminants on your experiments and how water is purified for use in the lab. She also offers practical advice on how to obtain the best water quality from your purification system.

This webinar explores:

  • How analytical instruments (HPLC, LC-MS, etc.) and experimental results may be affected by contaminants in your lab water
  • The main types of water contaminants and how various water purification technologies can remove them from your lab water
  • How to obtain the best water quality for your experiments

Read on for highlights from the Q&A session, or watch the webinar on-demand here.

Q: How long should we keep ultrapure water for UPLC use? We currently keep it for no more than seven days but are wanting to increase that limit.

A: We advise that you store it for as short a time as possible. Ultrapure water becomes contaminated very easily (from the container, from air, etc.). I understand that in some cases you need to store it. Depending on what you are doing with the water, it’s important to choose the right container; for example, since you are analyzing organics, then it is better to use a glass container. It also depends on the sensitivity of the technique you are using; if you are performing a very sensitive technique (UHPLC-MS) I would recommend you don’t store the water for very long.

The best technique would be to replace the water used for your mobile phase with freshly purified water every morning. If you protect it from the laboratory air with a bottle adapter, you may be able to keep it for a few more days. Seven days is already quite a long time!

Q: When I measure the pH of my pure water, it is not seven, do you know why?

A: It can be really complicated to measure the pH of ultrapure water because most of the techniques we have to measure pH rely on the presence of ions in water. If you are using ultrapure water, you will not be able to obtain a reliable pH value from a pH meter. If you wait for the meter to equilibrate, the CO2 from the air in your lab will start to dissolve into the ultrapure water and generate carbonic acid, bicarbonate and carbonate, making it slightly acidic. However, if you are using ultrapure water, you do not normally need to measure the pH because if the resistivity is 18.2 MOhm·cm, then the pH must be seven. As soon as there is the slightest contamination in ultrapure water that may affect the pH, the resistivity will no longer be 18.2 MOhm·cm.

Q: How is ultrapure water comparable to triple distilled water?

A: Triple distilled water is very high quality, but the concern when distilling is the container in which it is being stored. Furthermore, you have no easy way of measuring its purity, whereas with ultrapure water you can be absolutely sure what it contains since its quality is monitored by the purification system. I would also add that ultrapure water is much easier to obtain.

Q: Can I use the water that is dispensed from the water system right away or should I discard the first amount? If I need to discard, how much should I dispense?

A: If the system has been sitting idle (such as over the weekend), there is a risk that the tip of your system may have gotten contaminated by the lab air. I would discard a few liters of water before collecting water for really sensitive techniques. You can use the discarded water for less sensitive things, such as rinsing glassware.

Watch the full webinar on-demand, or find out more about the Milli-Q® systems.

Do you use any of the technologies mentioned in this webinar? Write a review today for your chance to win an Amazon voucher worth $400 or an iPad®.