Liquid Chromatography Blog

Enantiomer Separations

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...

MP Lifetimes

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...

Why Acid?

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 Follow-up

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...

Method Adjustment vs Change Part 7: Follow-up

In the previous articles in this series (Part 1Part 2Part 3Part 4Part 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...

Method Adjustment vs Change Part 6: Interactions

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.

Method Adjustment vs Change Part 5: Volume, Column Temperature and Detector Wavelength

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...

Method Adjustment vs Change Part 4: Flow Rate and Particle Size

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...

Method Adjustment vs Change Part 3: Column Dimensions

In this series on method adjustment vs method change, we first took an overview of the concept (Part 1) then at specific guidelines for mobile-phase adjustment (Part 2). In this article, we’ll take a closer look at some of the potential...

Method Adjustment vs Change Part 2: Aqueous-to-Organic Ratio

In the previous article (Part 1), we took an overview of the concept of method adjustment vs method change in reversed-phase HPLC, in light of the guidelines of the European Pharmacopoeia (EP) and United States Pharmacopoeia (USP). We also looked...

Method Adjustment vs Change Part 1: Overview

We all know that no HPLC method is perfect and that it may need to be “tweaked” once in a while to make it operate properly. But in today’s highly regulated environment, there’s always a question about whether or not such adjustments are allowed....

PEEK Fitting Slippage

PEEK (poly-ether-ether-ketone) fittings and tubing are in widespread use for HPLC applications. The convenience of using your fingers instead of a wrench to tighten the fittings and the flexibility of the tubing make PEEK the material of choice...

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