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. 

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?

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.

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. 

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.  

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.

Mixed mode Solid Phase Extraction (SPE) phases have become very popular for sample clean-up prior to analysis using mass spectrometry. Having the capability to retain compounds by two modes of interaction during SPE is useful when a large number of analytes with different properties are of interest.

How the acid dissociation constant (pKa) affects sample preparation method development? Knowing and understanding the pKa of your compounds tells you if the compound can be ionized, and under what conditions, so you can use this property to develop better sample prep methods.

Supported Liquid Extraction (SLE) is a sample preparation technique that has been in use for over ten years now, but many analytical chemists don’t know about, or understand the best way to do an SLE extraction.  In this post, I’m going to talk about how SLE works and the proper way to do an SLE extraction for sample clean up.

Understanding the chemical properties of the compounds in your sample matrix, both the ones you want to detect and the ones you want to eliminate, is necessary for successful method development. Is the molecule acidic or basic? What functional groups are present and can they be ionized? Is the molecule hydrophilic or hydrophobic? In this post, we discuss logP, and its role in sample preparation.