ovi method iv USP 467

[Murshad]

Hi

Has anybody had smooth sail while doing this combipal equipped with GC5890

I am having problem with RSD of 1,4-dioxane. After trying every thing I am thinking about chromatographic conditions described in method

As per method column is kept at 40°C for 20 minutes while injector is at
140°C

Finally I am thinking that 1,4-dioxane is recondensating at 40°C (boiling pt 100-102°C)

Would any body come to help.

Thanks with regards

[Peter Apps]

Hi Murshad

Unless you are grossly overloading the column with sample none of the sample componets will condense on the column n the sense of producing a droplet of liquid. What they will do is to partition stronbgly into the stationary phase (which is the basis of all chromatography) - a process known as stationary phase focussing, and this is to the good because all else being equal it should give you sharper peaks.

So, in other words, the starting temperature is not likely to be the cause of the problem.

Peter

[shaun78]

If you are referencing the new ovi procedure to become effective in 2008, then the USP does not require the RSD to be monitored. This is lergely due to the fact that only one injection each of the standard solutions are made at the beginning and end of each run ... which is also done because the run times are so very long.

I hold hope for future revisions of this procedure. As it stands, it is terrible.

[Schmitty]

If you are referencing the new ovi procedure to become effective in 2008, then the USP does not require the RSD to be monitored. This is lergely due to the fact that only one injection each of the standard solutions are made at the beginning and end of each run ... which is also done because the run times are so very long.

I hold hope for future revisions of this procedure. As it stands, it is terrible.

How does the EP feel about the method, as it seems the USP copied it from EP? (Or maybe vice-versa?)

[Murshad]

Hi Friends

Thanks for your reply. My injection volume is 1ml and this this method is part of GC calibration thats why I have to consider RSD.

Problem is only with 1,4-dioxane RSD.

Is there anly solution to avoid problem with 1,4-dioxane without changing anyparameter of the method.

Thanks

[AICMM]

Murshad,

Dioxane is problematic because it has a K value of 1618 (Restek Technical Guide on Static Headspace) which means it really does not want to partition into the headspace. I would be less likely to accuse the GC than I would the headspace process. I would also suspect your response is pretty poor.

Best regards.

[Schmitty]

I am using a LEAP Technologies CombiPAL on a 7890 with no issues for <467>. I was using a 5890 previously, but my management was kind enough to replace the aging unit.

I have no issues with reproducibility, typically running a standard before and after all samples. The autosampler method is VERY typical. 80°C heating, 85°C syringe, 20 minute incubation, short delays after pullup and after injection. The GC is set up as splitless, constant flow. I found with the 7890 that the peak shape for headspace analysis is very poor if no split is enabled, so I am not injecting 1mL, rather 250µL.

[Murshad]

Hi Schmitty

The method I am doing is iv. I cant change incubation time and vol. I have set combipal parameters as
Fill speed 300ul/sec
Pul up delay 5.0sec
Inject speed 300ul/sec
Pst inj del 1.0sec

what u suggest

Thanks with regards

[Schmitty]

What is your column flow? Your injection speed should not exceed the flow onto your column by too much.

The pullup delay is probably a little excessive, you could probably get away with ~ 500milliseconds or less.

Also, you mentioned that your %RSD was poor...what is the actual number?

[Murshad]

Hi Schmitty

Carrier velocity is 35cm/sec.

The only problem is 1,4-dioxane with RSD values about 20% while all other three are about 5 to 7%

my biggest problem at this time is 1,4-dioxane

For pullup delay should i try 500milli sesonds

[AICMM]

Murshad,

Schmitty wants flow not linear velocity. The idea behind this is that you don't want to push the syringe so fast that you push the sample out the split vent line or the septum purge line. Linear velocity speaks to column efficiency but does not help with the aforementioned issue. Two other items I think would be useful is column i.d. and whether or not you are splitting. The shorter pull up delay is to prevent the sample from leaking from the syringe before injection while still allowing some equilibration.

Best regards.

[Murshad]

Hi

At this velocity flow comes about 4ml/min. If we consider the leakage from syringe then problem with be all peaks not only 1.4-dioxane.

It is a splitless method
'
Thanks

[Schmitty]

Murshad,

With a column flow of 4mL/min (70µL/sec), you may be building up pressure in the inlet with your injection speed of 300µL/sec.

At what time does your 1,4-D elute at that column flow? Maybe you can increase the flow.

I don't recall <467> being all that strict.

[Murshad]

I am going to try three injections at 5.5ml/min flow with 500millisec

Hope every thing will be fine

I will let u know about outcome

[Murshad]

Hi

It did not work

RSD for 1,4-dioxane is way high and it eluted at 7.099 minutes


The only option now left use differenet manufactures for column


any idea