Liquid Chromatography

A reader asked me when it is appropriate or necessary to premix mobile phases when on-line mixing is available. For example, if a gradient is run from 95/5 buffer/organic (5% B) to 5/95 buffer/organic (95% B), should one bottle contain 95% buffer...

A reader asks, “I have a nice isocratic method for compound A, which elutes at about 8 min, so I can inject a new sample every 10 min. Occasionally, however, my samples contain another compound B that comes out at about 40 min. I have no way of...

A reader is trying to figure out the fate of a pesticide in water. For the test, he takes a soil sample (e.g., 5 g) and adds 100 mL of an aqueous solution containing 10 ppm of a pesticide. He takes 1 mL aliquots of the liquid phase each hour and...

What do you do if you receive the gift of an HPLC system of unknown breeding? In a recent enquiry, a reader indicated that when he moved into a new lab, the prior occupants left an HPLC system sitting on the bench. They thought it was working well...

How do you go about recovering a column that you suspect has some problems? Or perhaps you’ve pulled a used column off the shelf and want to make sure that it will work OK. Do you just dust it off before trying it, or is there a better approach?...

A question that comes up now and then in our Master Classes is how to figure out the volume of an HPLC column. I’d like to share a couple of rules of thumb that I find very useful for estimating column volume, V_M. Figuring out the volume inside the...

Did you ever feel like someone was out to get you? I remember the story one of my Master Class students told about leaving on a vacation. She left instructions with her lab mate to shut down her HPLC system the following morning after all the...

A reader recently asked, “The flow cell on my UV detector is completely blocked with some kind of white substance. I tried using a syringe to flush with water and with isopropanol, but neither was successful (and the process was very slow). The...

A reader recently submitted this question: “Most HPLC methods call for preparing the sample in mobile phase as the solvent. I like to avoid using some of the organic solvents for sample preparation because of toxicity issues, so most of the time I...

A reader asks, I would like to split HPLC column effluent between an evaporative light scattering detector (ELSD) and a fraction collector. What is the best way of doing this, particularly as we may want a biased split, i.e., 10% to detector and 90%...

A reader asks, “I am using a shared equipment where somebody used tetrabutyl ammonium (TBA) as an ion pair in their mobile phase for chromatography. It looks to me like the ion pairing reagent was not washed completely from the column, even though I...

A reader recently asked how to determine the column volume of a column packed with superficially porous particles. You’ll recall that these are a newer type of HPLC packing material, variously referred to as superficially porous, core-shell,...

A reader observed baseline drift in his gradient method and wondered where it came from and what could be done to eliminate it. There are two main sources of baseline drift – temperature and mobile phase. If the column is operated in a column oven,...

One of the topics in my HPLC Troubleshooting: A Performance Qualification Approach Master Class is the importance of knowing how your HPLC system works when it is working correctly. Knowing the normal detector noise and drift can help you to realize...

In HPLC Solutions #109 we discussed a technique to measure noise and drift for an HPLC detector. There are several possible sources of noise in the detector, and the approach to reducing or eliminating such noise depends on the noise source. For the...