rtx-624 resolution turn bad，just using half a year。

[dogcatlike]

as the title say。using rtx-624 to residual solvent analysis，new column resolution of acetonitrile and methylene chloride is 1.2，just half a year，now only one peak，not show any sign of isolation。what should i do？have to give up this column for this application? OR USING SOME METHOD TO TREAT THE COLUMN?

my application：USP467 Procedure A

[chromatographer1]

You may regain resolution by trimming 1-3 meters off the head of the column. Oxygen and trace contaminants damage the polymer, as does WATER in your samples. Still, no column lasts forever, and polar columns tend to have shorter lives.

Saying this, I generally found 624 columns to last 1-2 years.

best wishes,

Rod

[krickos]

I have the same experiance as Rod here.

Waht we do for non-specif procedure-dedicaded residual columns is that we semi-dedicate them for water and DMF/DMSO procedures, not just the WAX type columns for residual solvents but also 624 type columns.

Generally abit surprised would expect a Rtx column to last a bit longer, however there been some posted applications where certain critical resolutions may differ from brand to brand, but do not recall this particular resolution as an issue.

[dogcatlike]

how to use a column correctly，how to lengthen column life？
my headspace analysis，water as solvent，incubation temp 105 ℃，45min
mean more water into column。
not install carrier gas filter。
there must be some oxygen leak in，we not value the gas way airtight enough all the time。
once trimming 1-3 meters off the head of the column，when use column（parameter change），any influence to work？

[dogcatlike]

I have the same experiance as Rod here.

Waht we do for non-specif procedure-dedicaded residual columns is that we semi-dedicate them for water and DMF/DMSO procedures, not just the WAX type columns for residual solvents but also 624 type columns.

Generally abit surprised would expect a Rtx column to last a bit longer, however there been some posted applications where certain critical resolutions may differ from brand to brand, but do not recall this particular resolution as an issue.

thank u，but i can't follow u well。just know the main idea roughly。my experience must be abnormal？my clomn last too short，shorter than both of you？

[chromatographer1]

Allowing water to condense on the column interior CAN damage the column.

This happens if the initial temperature of the column is below 100C. (sound familiar?)

You can minimize this damage by putting a short piece of WAX column ahead of the 624 column [ see my paper in AC 1997 (69) p2221 ].

After some time one is required to remove a length of the column from the injector end, to remove this damaged part of the column. One to three meters is usually enough.

Of course, oxygen and other factors can damage the column as well which can be the cause of the shorter than normal service life of the column.

best wishes,

Rod

[Bigbear]

You can reduce the water on column by reducing your incubation temp. For DCM and ACN you should be able to go down to 40-50 C.

[dogcatlike]

You can reduce the water on column by reducing your incubation temp. For DCM and ACN you should be able to go down to 40-50 C.

for residual toluene assay，incubation 80 ℃ enough？toluene boil point 111℃。why in usp467，have a option of incubation temperature 105℃，when use this temperature？

now my incubation temperature is 105 ℃，oven temperature first stage，40 ℃，hold 20min。

what's DCM and ACN？mean dichloromethane and acetonitrile？

[dogcatlike]

Allowing water to condense on the column interior CAN damage the column.

This happens if the initial temperature of the column is below 100C. (sound familiar?)

You can minimize this damage by putting a short piece of WAX column ahead of the 624 column [ see my paper in AC 1997 (69) p2221 ].

After some time one is required to remove a length of the column from the injector end, to remove this damaged part of the column. One to three meters is usually enough.

Of course, oxygen and other factors can damage the column as well which can be the cause of the shorter than normal service life of the column.

best wishes,

Rod

you are excellent expert.

Initial oven temp:40℃，last 20min

‘putting a short piece of WAX column ahead of the 624 column [ see my paper in AC 1997 (69) p2221 ].’how to link well the two column，will lost resolution？

this damaged part of the column can be identified by eye.when one to three meters is cut，is there some difference in applying.

Which factor play first role in damaging the column？maybe hard to make clear

[Consumer Products Guy]

USP 611 for alcohol determinations injects water solutions on a 624 column. 624 columns can also be solvent-rinsed to restore performance; there are kits for this.

[chromatographer1]

I used a Fused Silica deactivated metal union (See Restek) or a fused silica connector (more delicate and requires more skill to use). If installed correctly there is no loss of resolution.

I used this combination of Wax and 624 column for 20-30 samples a day for 18 months before I replaced the Wax column and removed 3 meters of 624 column which then endured another 9 months before I replaced it.

Resolution of early eluting solvents improves although the order of elution changes. The only 'problem' is a coelution of MEK and Ethyl acetate.

DCM is an abbreviation for dichloromethane and ACN is acetonitrile.

The water in the HS injection plug is retained on the wax column until the temperature of the column is raised high enough so it migrates quickly through the 624 column and minimizes the damage of the water to that column.

best wishes,

Rod

[dogcatlike]

incubation temp：105℃，for water solvent headspace residual solvents analysis，why so high temp in usp467. it will influence peak area RSD obviously？have anyone used this incubation parameter，good result？

[jdezeeuw]

Such columns usually last a very long time. There are even more stable columns available using silphenylene groups. (Rxi-624Sil MS). If efficiency is lower, it usually is the inlet that has been attacked. Cut a section off (60cm = one-coil, to start with).

Other then that: you also can REVERSE the column. A bad section at the end has much lower impact on separation then a bad section at the front.

jaap de zeeuw, restek corporation

[dogcatlike]

good idea, you are very helpful, thanks a lot.