Decreasing the theoretical plates

Discussions about GC and other "gas phase" separation techniques.

10 posts Page 1 of 1
H
Hi folks just one question. I am using the DB-624 column with USP<467> method for IPA determination. Theoretical plates are 6000 but I want to decrease to 4000 or less without compromising the reproducibility. Any idea how I can do that


Thanks in advance
Hi Murshad,

Increasing the column ID and/or film thickness should help in lowering the plate count without affecting the reproducibility of the separation if this is the desired goal. Just check the USP requirements for the allowable adjustments and perform a verification study.
MattM
I agree with Matt.
Thanks for your inputs.

Actually I want to degrade the column to the level that plate count decreases to half. Changing the column dimensions or any modification in any operational parameter is not an option.

Thanks in advance
Hello again, Murshad,

You said:

Actually I want to degrade the column to the level that plate count decreases to half. Changing the column dimensions or any modification in any operational parameter is not an option.


Is it not the case currently that a GC column may be increased in ID by 50% and the film thickness by 100% by the USP?

https://www.fda.gov/downloads/ScienceRe ... 173085.pdf
MattM
Murshad wrote:
Thanks for your inputs.

Actually I want to degrade the column to the level that plate count decreases to half. Changing the column dimensions or any modification in any operational parameter is not an option.

Thanks in advance


I don't understand why one would degrade a column by purpose to get less plates?
If you have plates in excess you may trade them in for getting things done faster (higher flow rates or use shorter column).
But that seems not to be what you want.

other ideas: start overloading your column or use a suboptimal injection solvent/settings or make lousy connections to get your peaks broader... [/silly mode off]
Huh??

I don't want to change anything but I want to degrade the performance.

I don't get it.

Best regards,

AICMM
This does not make any sense at all. Why on earth would you want to reduce the plate count ?

Peter
Peter Apps
Making the column shorter will also decrease plate count (and can be done with current column assuming it is a capillary column).

Losing plates with out changing anything is not an option, it's physics.
Thanks,
DR
Image
I could see decreasing theoretical plates as being useful for prescribed methods, since there might be some compounds that have historically been reported as a coeluting singlet peak. With too much chromatographic efficiency, the singlet might be separated into a doublet and cause "errors" in the output relative to historical data. Similar requirements exist in many regulated sample prep methods, such as determination of lipids in solids for PCB conger analysis. The result could be more accurate, closer to the true value for lipids, but changing the method to improve accuracy will make it difficult to compare to historical data.

That said, the easiest way to reduce column efficiency (number of theoretical plates) is to change the flow from optimal. If you are currently close to optimal flow, slowing it a bit will increase your height equivalent of a theoretical plate and decrease the number of theoretical plates. If you have the luxury of increasing inner diameter or film thickness, this will also get you where you want to go, or by shortening the column.
10 posts Page 1 of 1

Who is online

In total there are 4 users online :: 0 registered, 0 hidden and 4 guests (based on users active over the past 5 minutes)
Most users ever online was 599 on Tue Sep 18, 2018 9:27 am

Users browsing this forum: No registered users and 4 guests

Latest Blog Posts from Separation Science

Separation Science offers free learning from the experts covering methods, applications, webinars, eSeminars, videos, tutorials for users of liquid chromatography, gas chromatography, mass spectrometry, sample preparation and related analytical techniques.
Subscribe to our eNewsletter with daily, weekly or monthly updates: Food, Environmental, (Bio)Pharmaceutical, Bioclinical, Liquid Chromatography, Gas Chromatography and Mass Spectrometry.
Follow us on Twitter: @Sep_Science

Liquid Chromatography

Gas Chromatography

Mass Spectrometry