Chromatography Forum

I am kind of curious. I keep reading literature and a lot of them are still using classical 1100 era column 4.6mm 25cm 5um columns even the recent papers from the past few years. No one seems to be publishing papers using SPP, sub 4um particles sizes etc. Is there a reason?

That's a great question. In our lab we essentially started with HPLC about 1980, and started using 2.1mm i.d. columns of 100mm length about a decade later (these were cartridge columns, the stainless steel holders got re-used). This enabled us to use 25% of mobile phase, and saved more because of less disposal costs. Linear velocity was kept the same, and this was on HP/Agilent 1050 systems.

Here are a few reasons columns were chosen in my lab:

• -It's a stationary phase only available in larger column dimensions (e.g. GPC)
  -Can run larger injection volumes for fraction collection
  -It was referenced in an older paper
  -It was in the column drawer and there's not enough budgeted for a new column
  -less sample prep required (e.g. no sample filtration)
  -Lack of training and experience
  -Equipment needs serviced/replaced to operate above 100 bar

I agree with Consumer Products Guy. This is an interesting question that more people need to ask themselves!

S_G's comments are very much on-point. I think a lot of it can be chalked up to inertia. The fact is that most people who publish papers using chromatography are not chromatographers. I don't mean that to be disrespectful: they are pharmaceutical chemists, biochemists, environmental chemists, or whatever, and chromatography is a tool. In many cases it's not even the most important tool, so as long as it does the job there is little incentive to seek out the latest and greatest.

To put this in perspective, I'm writing this on a 5 year-old Windows laptop that was mid-range even when it was new. Sure, there are better/faster/lighter machines available today, but as long as this one does the job, there is little incentive for me to upgrade.

In many cases it's not even the most important tool, so as long as it does the job there is little incentive to seek out the latest and greatest.

This absolutely true. For example, in developing a new assay for a pharmaceutical active, if column "A" separated the sought-for analyte well from the product matrix, and I could complete the assay run in a reasonable amount of time (isocratic, if I could), then there would be no incentive to explore other columns to see if the resolution was even better. Then we would order brand-new columns for the validation studies. There would be financial considerations if we were fortunate-enough - or if I was good enough - to stay with column types that could be used with some of our other assays.

To put this in perspective, I'm writing this on a 5 year-old Windows laptop that was mid-range even when it was new. Sure, there are better/faster/lighter machines available today, but as long as this one does the job, there is little incentive for me to upgrade.

Ha !!!! I'm using a Dell laptop (purchased used) and Windows 7 !!!!

If you're in a regulated environment, there might be a big disincentive: if you have to revalidate your method, it might be cheaper to carry on using the validated 1990's method. It annoyed me enormously during the Great Acetonitrile shortage, because ACN was rationed by the suppliers, who were (quite rightly) favouring those who had important applications; but important applications tend to be in regulated environments, and therefore were more likely to be running 1mL/min 40min methods on 250*4.6mm columns, while at the time I was running 0.3mL/min 10min methods on 50-100*2mm columns.

There is a theoretical consideration too. Very roughly: If you halve the particle size, you double the number of theoretical plates, so you can get the same resolution out of a column half the length. Halving the length would normally halve the back-pressure, but halving the particle size will roughly quadruple the pressure, so the net change is same resolution at twice the back-pressure, but with half the run time if you keep the flow-rate the same. So actually, small particle sizes in modern columns are about fast run-times, not about increased resolution. If you really need high plate-count to get adequate resolution, and you are limited by the back-pressure capabilities of your pump (as we all are, ultimately, even if you have a UPLC pump), then there comes a point where you need long, big-particle columns, not short, small-particle columns. For this reason, you will still find a few people making an informed choice of a 250mm columns instead of reaching for 1.7u particles.

If you're in a regulated environment, there might be a big disincentive: if you have to revalidate your method, it might be cheaper to carry on using the validated 1990's method.

My last pointy-haired boss (see Dilbert) did not believe the written text in USP <621> or FDA ORA documents which detailed what modifications could be made WITHOUT having to re-validate. I even sarcastically mentioned that when I was in kindergarten that I learned 26 letters which would make up words, and then these words could be read by all.

If you're in a regulated environment, there might be a big disincentive..... It annoyed me enormously during the Great Acetonitrile shortage, because ACN was rationed by the suppliers, who were (quite rightly) favouring those who had important applications; but important applications tend to be in regulated environments, and therefore were more likely to be running 1mL/min 40min methods on 250*4.6mm columns, while at the time I was running 0.3mL/min 10min methods on 50-100*2mm columns.

I had already changed our company over to narrower-bore HPLC columns before that ACN shortage. We used ACN in most of our regulated/validated test methods. It turns out that our production QC labs had enough ACN for several months, and so did we. I was able to purchase ACN already containing acetic acid to use in a couple of non-regulated methods, as were were using acetic acid-water as the aqueous phase for those anyway.

However, my pointy-haired boss (see above) felt that we should re-validate most of our regulated methods using methanol as the organic phase, which we ended up doing for assays which did not build up too much column pressure. But we never did switch to methanol for those at either R&D or QC, but did expend a lot of time/effort for that project.

The same pointy-haired boss also felt that the world's supply of helium was going to dry up so he had the company hoard cylinders of helium, paying cylinder rentals for years. Last time I walked by Dollar Tree, they had helium tanks for filling balloons; yes: they were $1 !!!