Liquid Chromatography Blog

I had a follow-up enquiry about one of the recent articles. In 'Why Acid?', I discussed some of the reasons why acids such as formic or trifluoroacetic (TFA) are added to mobile phases for LC-MS work. The reader noted that in Figure 1 of that...

Q: I am running an isocratic method with a 250 x 4.6 mm, 10 µm particle column at 1 mL/min with a 20% acetonitrile (ACN)/buffer mobile phase. I dissolve my sample in ACN and inject. Normally my compound of interest comes out at 7.7 min. I...

In a recent email, a reader enquired about the best way to clean the frits used in the HPLC system. He indicated that he had been sonicating them in nitric acid, but wasn’t sure if that was the best way to approach the problem.

A reader complained about retention times that changed in an overnight HPLC run and wondered how to diagnose the problem source. The question left too many possibilities, and because there was no complaint about changing resolution, I’ll assume...

Recently, a reader sent a question about how to get started with a method that required separation of enantiomers by reversed-phase HPLC. Unfortunately, the problem is a non-starter in this context. Enantiomers cannot be separated by...

A reader recently sent in this e-mail: “I am trying to find information that I can put in an SOP regarding how long a mobile phase can be used before it must be discarded. I’ve heard 1-2 weeks from some sources, whereas others say a month, and...

Recently, I received an email from a reader asking why formic acid was specified as an additive for the mobile phase in an HPLC method he was using. Formic or trifluoroacetic acid at 0.1% concentrations are common, especially for LC-MS work....

PEEK (poly-ether-ether-ketone) tubing and fittings have become a standard part of most HPLC systems today. The flexibility and ease of cutting the tubing, coupled with the convenience of finger-tightened fittings make a combination that is hard...

In the previous articles in this series (Part 1, Part 2, Part 3, Part 4, Part 5, Part 6), we have explored the concept of the adjustment of HPLC methods. In particular, we have tried to determine the difference between method adjustment and...

This is the last in a six-part series on allowed adjustments to HPLC methods. In the previous instalments (Part 1, Part 2, Part 3, Part 4, Part 5), we’ve looked at each of the specific variables listed in Table 1.

In the last few articles we've focused on the guidelines for method adjustment listed in the European Pharmacopoeia (EP) and United States Pharmacopoeia (USP). We looked at pH (Part 1), mobile-phase composition (Part 2), column dimensions (Part 3...

In prior instalments of this series on method adjustment, we’ve looked at the guidelines from the European Pharmacopoeia (EP) and United States Pharmacopoeia (USP) for allowable adjustments in pH (Part 1), mobile phase (Part 2), and column...