DCM in water

[push]

I need to analyze ppms of dichloromethane in water. Can I inject water solution onto the GC column? Which column is more stable at such conditions:DB-1 or DB-WAX?

[Consumer Products Guy]

DB wax is more compatible with water injections, but keep injection size 0.5ul or less, water expands a ton.

Personally, I'd consider headspace for this.

[cleh]

Agree with CPG, headspace or purge and trap.

[chromatographer1]

Water will damage capillary columns if allowed to condense into a liquid. At the temperatures I would expect you to do this analysis you will damage both types of column.

Which column could you dedicate to this analysis and not use for other projects?

If you can find a porous polymer column, packed or capillary, that column would be an excellent solution to your needs and it would not be damaged by water injections.

Consider this alternative if you intend to do this testing for any length of time. It would cost you the same to replace a damaged column as to buy a new porous polymer column which is a better cost effective solution over any length of time.

best wishes,

Rod

[James_Ball]

Another easy solution would be to use SPME (Solid Phase Micro Extraction) for this analysis if it will be an ongoing series of analysis. If it is a one off test then any column should survive a couple injections.

I know I have had a Restek Rtx502.2 column(105m x 0.53mm x 1.4um film made especially for volatiles) that was completely filled with water when a purge and trap overfilled and desorbed water directly to the colum that survived with no problems at all. Just baked it out a couple days and neither the column or the mass spec had any problems, but I would not recommend it as a normal practice.

[gcguy]

I have never seen any issue with columns being damaged by injecting water. For bonded phase columns most maufacturers suggest water as part of the rinsing regime to clean up columns. I have used water/meoh/DCM as the solvents to back flush GC columns. The only precaution was to heat the column very slowly after re-installation to allow the phase to "dry out" slowly.
All the problems I have encountered with water wet samples has been around getting reproducible results from a split injector, especially when the solvent of interest forms an azeotrpe with water. Most of these issues can be fixed by using an on-column injector.

GCguy

[aldehyde]

"how wet can you get" presentations from agilent and advanstar:

http://www.chem.agilent.com/Library/ese ... ctions.pdf
http://www.chromatographyonline.com/lcg ... rticle.pdf

[chromatographer1]

To offer my summary based on experience,

for almost all bonded phases,

if the water is placed on the column at temperatures and amounts where the water plug remains a vapor there is usually no or little damage to the column.

if the water is allowed to condense to liquid it can cause damage to the column, especially if the phase is polar. This can be very noticeable where PEG phases are being used. The bonding chemistry for PEG phases and their derivatives is involved.

But for non-bonded phases, water is not recommended and can cause damage to the uniformity of the coating of the phase on the column surface, effecting changes in peak shape and retention times of peaks.

For porous polymer supports water is usually not an issue.

Water of course, should never be injected on molecular sieves which are not carbon based.

best wishes,

Rod