This is a frequently asked question based on a long history of water injections in gas chromatography. As time goes by, the rules often change.

In the first GC columns, gas chromatography phases were simply coated onto the column. This was mostly the case with packed columns, but also the same with the very first capillary columns. Injecting water onto these phases dissolved the phase and caused the phase to elute from the columns.

Over time, the capillary columns were bonded instead of coated. This chemical bonding made them stable to water injections, as well as solvent rinsing.

Today, most GC columns are chemically bonded—meaning that water will not remove the phase from the column. Therefore, bonded columns are chemically stable to water injections and can even be column rinsed with water.

Very polar phases like PolyEthyleneGlycol (PEG) based columns are so polar that the water can build up over time and cause slight changes in the phase. Even though this will not remove the phase, it is advisable that water injections be limited on most PEG based phases for this reason.

There is only one other consideration for GC and water injections. The expansion volume of water when vaporized is HUGE! As an example, 1.0 uL of water will expand to over 1200 uL in a 225°C inlet with a 12psi head pressure. By contrast, 1.0uL of isooctane will only expand to 136 uL of volume under the same conditions. This large expansion volume for water does need to be taken into account.  If the expansion volume is larger than the volume of the liner, then the vapor will back-flush into the gas supply lines which are not heated and cause persistent sample carryover. Small injection volumes are therefore recommended for water.

One common application that utilizes water as a matrix is volatiles. Because the analytes are volatiles, a higher elution temperature might not be necessary to elute the analytes; however, this can leave the water and other higher boiling contaminants on the column. If using low temperatures, the water (even from headspace injections) will remain on the column until eluted. This water complements the polarity of the phase and alters the separation. The water will need to be routinely baked off of the column to restore performance.

So, basically…

• Most of the hesitation about water is due to stories about column instability from when columns were coated instead of chemically bonded. There are still a couple of coated columns available, but most have taken a more modern route.

• The only consideration with bonded columns is injection volume / expansion volume and possible buildup at low temperatures. Successful water injections can be performed by keeping these two factors in mind.


Related resources:

Gas Chromatography Technical Tips
• Gas Chromatography Columns and Accessories
Polycyclic Aromatic Hydrocarbons (PAHs) in Water by Zebron ZB-5MS
Hydrocarbons from Water DIN EN ISO 9377-2
Dispersants in Seawater on a ZB-Waxplus 30 x 0.25 x 0.25 by GCMS

7 thoughts on “Is Water Safe To Inject In Gas Chromatography?”

  1. Very well for bonded phases, but aren’t most liner deactivations coatings (and those of guard columns) susceptible to hydrolysis?

    1. Hi Steve, thanks for reading! That’s a great question.

      Yes, they are susceptible, along with the metal inlet seal and any glass wool if it is used. Over repeated injections and at high temperatures, water can hydrolyze any siloxane-based (which are the most popular) deactivations on these components, leading to increased activity which manifests as peak tailing in the chromatogram.

      A good rule of thumb is to regularly change out the liner (depending on the sample matrix, type of sample preparation, and number of injections) and, when feasible, use the smallest injection volume necessary to achieve sufficient detection and sensitivity limits.

      Hope you’re enjoying the blog! We always love hearing some audience insight. Please follow us, if you wish, and come back soon! 🙂

  2. I am curious what kind of split ratio you would use for injecting pure water. Also one thing to consider, would you ever recommend diluting water with a common solvent?

    1. Hey Justin! Thanks for perusing the blog.

      Split ratio for GC analysis should be optimized based on the goal of analysis. For example, if the sample is very concentrated, then higher split ratio should be used. However, if the analytes are in trace level, then low split ratio or splitless mode should be used. So, the split ratio optimization is irrespective of the solvent used and depends on analyte concentration.

      Water : methanol, water ethanol, DNF water, DMSO water can be used. Since water has high thermal expansion in the inlet, it is not commonly used as mixture with other solvent. However, in headspace GC analysis, water : DMF/DMSO is common.

      We appreciate the feedback, and hope you find your way here again soon! Please follow or subscribe for more GC goodies. 🙂

  3. So I stumbled across this post as I was researching some water only autosamplers. Was curious if you had any recommendations, and further more if you have any experience with or feedback on the EST Analytical Centurion

    1. Hi Ryan! So glad you stumbled upon us. 🙂

      I spoke to some colleagues with experience in this topic, and this is what they had to say:

      “Tekmar was THE company for this back in the day, and I assume they are still leaders in the field:

      An important distinction here is that purge and trap (P&T) does not in fact inject water into the GC system. It bubbles (purges) the volatiles out of water, and traps them onto a . . . trap (looks sorta like a long skinny HPLC column) which then desorbs into the GC similar to headspace. If you are looking to inject straight-up water, that is doable, but an entirely different thing.”

      Let us know if that helps, and please don’t hesitate if you have further questions!

Leave a Reply