Archive for the ‘LC-MS/MS’ Category

Why is my LC Retention Time Shifting?

If you have experienced retention time shifts with LC, you know it can be complicated and can cause problems with quantitation if not resolved. Hopefully this post will help you navigate through troubleshooting this situation. For the purposes of this discussion, we will be discussing changes in retention on one individual column, not differences from […]

Chiral separation on a C18 column? Separation of d- and l-amphetamines, Part II

To continue my blog part 1 (Part 1:https://blog.restek.com/?p=67087) , where I have briefly discussed the importance of separating the d and l isomers to accurately identify the illicit isomer using an achiral method on a Raptor C18 column employing a pre-column derivatization technique. Today I’d like to discuss more about the matrix of interest, sample […]

Falling Victim to One of LC’s Classic Blunders: Mismatching Your Diluent and Mobile Phase

An early lesson most of us learn in liquid chromatography is this: Always match your diluent to your mobile phase.  Once the exams are done, if you learned this in a college course, or your manager has walked away, you start flexing this “requirement” a little to see how matched they really need to be.  […]

Determining Optimal LC-MS/MS MRMs: Sensitivity is NOT Everything!

LC-MS/MS using electrospray ionization (ESI) is a widely used platform for routine target analysis and quantitation. However, one big challenge faced through the use of ESI is the presence of matrix effects. So, what are matrix effects and why are they important? Simply put, when matrix components coelute with the target analytes, they have the […]

Chiral separation on a C18 column? Separation of d- and l- Amphetamines, Part I

Did you know that chiral chemistry was discovered by Louis Pasteur, a French chemist and biologist in 1848? However, it took about a century to find that chirality plays a key role not only in the life of plants and animals, but also in several aspects of drug design, and both pharmaceutical and illicit drug […]

Afraid of HILIC? Watch These Videos and Overcome Your Fear!

Hydrophilic Interaction Liquid Chromatography or HILIC is a powerful tool to analyze polar compounds that have limited retention on typical reversed-phase columns. The power of HILIC can be utilized across multiple markets including environmental, food safety, and clinical diagnostics. But to be honest, it can be challenging to implement a HILIC method and more considerations […]

Pesticides are like Siblings – some get along well and some don’t – No. . .Really?

My colleague, Joe Konschnik and I have been asked by many food chemists out there about how much they can trust their pesticides mixes after they combine them into one single larger mixture for calibrating their instrument, or monitoring the accuracy and precision of their method – and rightfully so.  Well, like siblings, sometimes they […]

What are GenX and PFBS? Why are they important in PFAS analysis?

Analysis of PFAS (per- and polyfluorinated alkyl substances) has been a hot topic for envoironmental labs for the last several years. Currently there are two C8 based PFAS compounds (PFOA and PFOS) with a health advisory level of 70 ppt in drinking water announced by the US EPA. In 2018 at the National Leadership Summit, […]

Sorry for the delay. Here is your chromatogram with and without the PFAS Delay Column.

Sometimes I hear this from customers: “I don’t need a delay column. I haven’t had any trouble without it so far.” It might be true. You may not have any issues without the delay column, especially when your samples are, for example, highly PFAS contaminated soil samples because the interference is too small to affect […]

What’s in a name? A C18 by any other name would not be the ARC-18

You have probably read or been told numerous times and in numerous ways that not all C18 columns are the same. And that is very true. Particle morphology, bonding chemistry, and add-ons like end capping all influence the retention and selectivity of this workhorse LC phase. At Restek we have an interesting C18 phase that […]