DI water or HPLC water for mobile phase?

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

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DI water or HPLC grade water? any particular requirement for the method mobile phase?

Your method should specify which grade of water to use. If it does not, I would default to HPLC grade water.

The method is using DI water, but I don't understandard the reason. Is DI water and HPLC water equivalent?



Blazer wrote:
Your method should specify which grade of water to use. If it does not, I would default to HPLC grade water.

I assume you're considering Chromasolv water vs house DI?

In which case, the difference is in the impurities and ionic strength. Chromasolv has lower magnitude of both.

If your method is calling for house DI, I suspect that:

1) Ionic strength won't measurably affect your separation.

2) Your analytes are at a high enough concentration compared to the impurities.

3) You filter your mobile well and use a guard column.

I wouldn't put DI in any of my columns, but that's because I don't want to replace them any quicker than necessary.

[quote="flora0975"]The method is using DI water, but I don't understandard the reason. Is DI water and HPLC water equivalent?

Well they can be - if you use DI in your HPLC :-). In general, DI water is expected to contain more impurities than HPLC water, which usually has been through extra steps to remove the last residues of ionic impurities, as well as many organic species using carbon and UV stages. Some detectors may not like DI water.

Both Chromatography grade and DI are often sterile-filtered ( 0.22um ) at point of use, which is adequate for most HPLC work, unless the instrument/column manufacturer specifies otherwise.

Bruce Hamilton

HPLC grade water quality varies significantly. Someone found "HPLC Grade" water that came in plastic bottles. As expected we saw significant impurities when running a gradient with UV detection.

I've had good success with Burdick and Jackson HPLC Grade water. For most work I use water from a Milli-Q DI system. It is HPLC grade and as good or better than Burdick and Jackson.

ASTM D1193 lists some quality parameters for Type I water:
Resistivity: 18 Mohm.cm
TOC: <50 ug/L
Sodium: <1 ug/L
chlorides: <1 ug/L
silica: <3 ug/L

Hope this helps.
A. Carl Sanchez

Thanks for your reply!

In the method, it is said to use distilled or deionized water, further purified using Millipore Milli-Q or equivalent system.

Since we don't have high quality in-house DI water, I am always using HPLC grade water and didn't see any problem so far. I am wondering except impurity / particle concern, DI and HPLC water should be same.
We recently purchased a high end LC-MS/MS system and the vendor assured us we can safely use Milli-Q water as mobile phase for which we have an in-house purification setup. It is of course important to maintain and monitor the quality of this water.

For other HPLC and LCMS setups, we have been using HPLC/LCMS quality water up to now. If it's fit for a high end LCMS setup, it should be fit for HPLC as well. So we're looking into gradually replacing the use of HPLC/LCMS water.
I would never recommend using DI water in an HPLC system. You invest all that money in an advanced chromatography system which relies on the ultra-high purity of the mobile phase, columns and flow path to provide scientifically accurate results, then put "DI" water in it???? DI water is by definition not even filtered for particulate matter. A very bad choice in my opinion and one that should result in method failure by any trained auditor or industry chromatographer.

For more information, I wish to recommend this article: "What type of Water Should I use for HPLC, UHPLC or LC/MS Analysis?" https://hplctips.blogspot.com/2013/10/w ... e-for.html
have to disagree I'm afraid, though it depends what you define as "DI" or Milli-Q. We use 18.2MOhm water from a purifier with a 0.2u filter on its outlet, and get the water purifier serviced regularly according to its instructions, and we've only had one water-related issue in the last 15 years (that was with pulsed amperometric detection in a Dionex ion-chromatography system, where we have since stuck to electrochemical grade water).
If you're a reasonably high throughput lab, then bottled HPLC water is fine. Where it's more risky is if you're a more occasional user (e.g. some university labs where the instrument is multi-user, and a group might maintain their own solvents, but sometimes not use the instrument for a few weeks). In this case there is a real risk of algal growth and contamination in the bottled water once it's been opened; LCMS-grade water is only LCMS-grade when it's supplied, not two weeks after someone's opened the top and let the bugs in.
Personally I always replace water/aqueous solvents after 24 hours.
I have only used DI water that was filtered (0.22 um) for a RID. For a UV/PDA/DAD I would use a low TOC water like an HPLC water (Burdick and Jackson).
I have been able to use 3 Megaohm DI water from a Culligan system on an LCMSMS and had good results. It mostly depends on the test you are doing. If there are impurities that interfere with the analysis then the water is not good enough, no matter where it comes from.

I have tried to use HPLC grade water in our Purge and Trap analysis for volatile organic compounds on GC/MS and had high levels of Chloroform impurities that made it unacceptable, but in an HPLC application that will not cause any problems at all.

When you read up on most recent applications from the instrument manufacturers the specify using Milli-Q or equivalent water. DI really isn't an accurate specification for water, better to refer to Type I, II or III https://puretecwater.com/deionized-wate ... -standards
The past is there to guide us into the future, not to dwell in.
18.2 Megaohm DI water is used all the time in pharma labs for HPLC without issues. I find that LCs with MS prefer LCMS grade bottled solvents.
Im not sure if a UV could tell the difference but any MS will.
BostonFSE wrote:
18.2 Megaohm DI water is used all the time in pharma labs for HPLC without issues. I find that LCs with MS prefer LCMS grade bottled solvents.
Im not sure if a UV could tell the difference but any MS will.


Can you elaborate how the MS will easily tell the difference between different grades of water?
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