2017-6. Method Adjustment the USP Way

When you want to adjust a United States Pharmacopoeia (USP) method for a different size column or to meet system-suitability criteria that fail, how much of a change can you make without revalidating the method? LCGC 35(6) 368-373 (2017) John W. Dolan  

Read More →

2015-4. Be Careful of the Flow Rate

When converting methods from liquid chromatography (LC) to ultrahigh-pressure liquid chromatography (UHPLC), don’t get confused by flow-rate settings. LCGC 33(4) 248-253 (2015) John W. Dolan

Read More →

2014-8. How Much Retention Time Variation is Normal?

Small changes in retention time of a liquid chromatography (LC) method are normal. At what point is a problem suggested? Retention time shifts can be frustrating when you can’t figure out if a shift is something you caused or if there is another reason for it. LCGC 32(8) 546-551 (2014) […]

Read More →

2013-5. Gradient Elution, Part III: Surprises

Sometimes when changes are made to gradient conditions, the result isn’t what was expected. LCGC 31(5) 382-389 (2013) John W. Dolan ERRATUM: The last word on p. 388 should be “decrease” not “increase.” A change in particle size from 3 microns to 5 should reduce the pressure, not increase it.

Read More →






2003-4. Flow Rate and Peak Spacing

Flow-rate changes might or might not be acceptable means to adjust retention. LCGC 21(4)350-354 (2003) John W. Dolan erratum: text associated with equation 3 should have stated “If the flow rate is halved from 2 mL/min to 1 mL/min k* is halved.”

Read More →