Guard column ID matching

[Peggsy]

G'day from Perth

I am purchasing a 250 * 4.6 mm (5um) analytical SAX column and have multiple choices as to what ID i can get the guard column in. Price wise, the 20 * 4 mm option is the best, compared to the best ID match of 17*4.6 or even 40*4.6 mm guards.
Flow rate: 1ml/min
Mobile: PO4 buffer with MeCN, gradient

I would apprciate any comments on the pros and cons, if any, of choosing a guard with a smaller ID than the analytical column.

i would imagine that with the 4 mm rather than 4.6 mm ID guard, backpressure may be a little higher, but of course with the guard being very short, this increase would be minimal. Sample plug i would imagine would be 'tighter' with the smaller ID guard.....

thanks for any comments

Greg

[tom jupille]

From the point of view of chromatographic performance, it probably doesn't matter very much, with a slight edge toward the smaller id as representing a smaller fraction of the total stationary phase volume. If your samples are very dirty, the larger id will last longer.

[Peggsy]

Thanks Tom, as i expected, but nice to hear some affirmation.

BTW, we meet at the HPLC troubleshooting course at HPLC 2012 Anaheim, I'm the Aussie guy!

cheers
Greg