Chemical Grades of Water

By Jillian Jastrzembski

Not all water is created equal, especially in the laboratory. It’s important to know which type of water to use for each application in order to achieve reliable results, preserve the life of your equipment, and save money.

To make things simple, we’ve created a quick guide on the different types of water available at Lab Alley.

At Lab Alley, we currently supply four types of water, including:

• LC/MS grade water
• HPLC grade water
• Deionized lab grade water
• USP Grade Water

We’ll give a brief overview of each type and resolve some common mix-ups.

LC/MS Grade Water

LC/MS stands for liquid chromatography – mass spectrometry. This grade of water is suitable for high purity applications, especially mass spectrometry. Using this high purity water for mass spectrometry applications will help you minimize maintenance on your analytical instrumentation. It will also help you get a lower baseline for improved sensitivity.

HPLC Grade Water

HPLC stands for high performance liquid chromatography. This grade of water is also high purity, though not as strict as LC/MS grade. Read on to understand more about the difference between HPLC and LC/MS grade water.

Deionized Water Lab Grade

This is the least pure of the listed categories. Deionized lab grade water is different from water out of the tap because it doesn’t contain any minerals or ions, so it has a very low conductivity. While it isn’t quite pure enough for analytical applications, it is perfect for general lab tests like pH or the final rinse during cleaning.

USP Grade Water

USP is a chemical standard that is regulated by the United States Pharmacopeia, a non-profit independent organization that sets regulations for chemical purities and specifications. USP is an internationally recognized standard that is essentially interchangeable with pharmaceutical grade.

HPLC vs LCMS Grade Water: Is there a difference?

Yes, and it’s a fairly important one. As you might expect, you should use HPLC grade water for HPLC, and LCMS grade water for mass spectrometry applications. LCMS grade water has higher purity compared to HPLC grade.

It’s ok to use LCMS grade water for HPLC applications, because that would mean you are using a higher than necessary purity.

However, the opposite is not true. If you are working with mass spectrometry, and you downgrade to HPLC grade water, you will get worse results and cause damage to your instrument in the long run.

Let’s break down the difference:

HPLC is an analytical technique that stands for high performance liquid chromatography. LCMS stands for liquid chromatography mass spectrometry.

Both of these involve the same separation principal in which a mobile phase that carries a sample through a stationary phase. The components of the sample will separate based on their relative affinity for the stationary phase and the mobile phase. The mobile phase is a system of solvents, which often includes water.

As the sample components elute, they are detected by a detector and the signals are displayed on a chromatogram. Both the stationary phase and the mobile phase can be changed to improve the separation.

Since they are basically the same, it seems reasonable that we should be able to interchange HPLC grade water for LCMS grade water – but that isn’t the case. The key difference is in the type of detector being used.

HPLC grade implies that the water is suitable for UV detection. Since it’s an analytical technique, we should use high purity, HPLC grade water. What determines if the water is pure enough? The concept of “clean” water in this case means that it won’t react with UV.

Now let’s look at LCMS, which uses mass spectrometry as the detection method. A mass spectrometer detects the mass to charge ratio of the ions in the sample.

And that’s really the key – because there are lots of things that are invisible to a UV detector, but they definitely have a mass, and most of them will ionize.

Downgrading to HPLC grade water for LCMS applications poses two problems:

1. You will see impurities from the water, which compromises the integrity of your analytical method. You will get a higher baseline and reduced sensitivity.
2. You will put stress on the components of your mass spectrometer, which will give you a lot of maintenance issues, and potentially shorten the lifespan of your expensive instrumentation.

So, while it can be tempting to reach for the cheaper option that seems basically the same, you’ll actually be losing money and results in the long run. Stick with LCMS grade water for mass spectrometry.

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