Stephanie J. Marin, Ph.D.
Recent Posts
How to choose the best elution solvent for SLE?
September 24, 2021 at 2:18 PM / by Stephanie J. Marin, Ph.D. posted in SLE Supported Liquid Extraction, Sample preparation, extraction, solvent polarity, elution
How do I pretreat my samples for Supported Liquid Extraction
July 14, 2021 at 6:09 PM / by Stephanie J. Marin, Ph.D. posted in SLE Supported Liquid Extraction, Sample preparation, extraction, pretreatment
Correct pretreatment of samples prior to supported liquid extraction (SLE) produces better partitioning and cleaner extracts. Supported liquid extraction (SLE) is a simple clean-up technique similar to liquid-liquid extraction (LLE), but on a solid supported surface.
Why should I underload SLE+ plate or cartridge?
July 7, 2021 at 7:00 PM / by Stephanie J. Marin, Ph.D. posted in SLE Supported Liquid Extraction, Sample preparation, extraction
Underloading your SLE+ samples can result in better partitioning and cleaner samples. Supported liquid extraction (SLE) is a simple clean-up technique similar to liquid-liquid extraction (LLE), but on a solid supported surface.
When should I choose SPE instead of SLE?
October 9, 2020 at 8:00 AM / by Stephanie J. Marin, Ph.D. posted in SLE Supported Liquid Extraction, SPE solid phase extraction, Solid-phase extraction
When would I choose SLE? When would I choose SPE? We all have faced those questions. Let's have a look at the two sample preparation techniques.
Protein precipitation vs. traditional protein crash: what's best?
October 7, 2020 at 8:00 AM / by Stephanie J. Marin, Ph.D. posted in Sample preparation, Method development, Protein precipitation
Most clinical chemists have developed a blood, serum or plasma assay using a protein crash because it is inexpensive and generally removes proteins that interfere with detection or the analysis in some way. But is this always true?
How do I Develop a Sample Prep Method?
October 2, 2020 at 8:00 AM / by Stephanie J. Marin, Ph.D. posted in LC-MS, Sample preparation
This is a question that I am often asked by very smart people that just haven’t had time to learn the process. An optimized sample preparation method is critical for an accurate, specific, robust clinical LC-MS/MS assay. A good sample prep method can improve accuracy and precision, provide longer LC column lifetime, and keep your LC-MS/MS system clean.
What is Crosstalk and how do I Prevent it from Contaminating my Samples?
September 18, 2020 at 1:47 PM / by Stephanie J. Marin, Ph.D. posted in amphetamines, contamination, false positive result
Evaporative crosstalk is contamination that occurs during evaporation of the elution solvent after SLE or SPE extraction. Volatile analytes evaporate, then redistribute in adjacent wells in a 96-well plate. This can generate false positive results and require re-extraction of patient specimens. Addition of HCl in methanol (MeOH) to produce the salt of volatile compounds like sympathomimetic amines is used to control crosstalk. The type of evaporator, conditions and solvents used can all contribute to crosstalk.
Methods for a drug class or one large panel - what's the difference
August 23, 2020 at 8:00 AM / by Stephanie J. Marin, Ph.D. posted in LC-MS, GC-MS, Extraction method optimization, Sample preparation, Method development
Most clinical and forensic labs have a used a traditional approach for drug testing called screen with reflex to confirmation. This involves analyzing samples using an immunoassay technique that identifies a drug class. Positive immunoassay results are then analyzed by a second more specific method, like GC-MS or LC-MS/MS, to identify and quantitate specific drug analytes.
When should I choose weak ion exchange SPE phases?
July 8, 2020 at 3:17 PM / by Stephanie J. Marin, Ph.D. posted in SPE solid phase extraction, Extraction method optimization, Sample preparation
What is a weak ion exchange SPE phase? What is their charge state and how they behave in function of pH conditions? When to choose them? This post will describe Biotage mixed mode weak ion exchange SPE phases - EVOLUTE EXPRESS WCX and EVOLUTE EXPRESS WAX - and how to optimize your sample preparation of your analytes of interest.
When should I choose a mixed-mode SPE?
July 8, 2020 at 3:15 PM / by Stephanie J. Marin, Ph.D. posted in SPE solid phase extraction, Evolute Express AX, Evolute Express CX