Why is Liquid Chromatography Coupled with Mass Spectrometry (LC-MS) Favored for Pharmaceutical Bioanalysis?

Forensic laboratories and doping laboratories perform bioanalysis to detect substance misuse in criminal trials and sports.

FREMONT, CA: Pharmaceutical bioanalysis includes detecting and quantifying drugs in biological fluids such as human blood plasma, serum, whole blood, urine, and saliva. Furthermore, hospital laboratories carry out bioanalysis to ensure if patients are appropriately medicated and compliant.

Bioanalysis is carried out by the pharmaceutical industry during drug production and clinical trials, for pharmacokinetics and toxicokinetics, and ADME (Adsorption, Delivery, Metabolism, Excretion) research linked to new drug substances. Analytical services contract laboratories also perform the above type of measurements. Besides, forensic laboratories and doping laboratories perform bioanalysis to detect substance misuse in criminal trials and sports. Bioanalysis is thus of immense interest to society and is a very active scientific discipline.

Liquid Chromatography, coupled with Mass Spectrometry (LC-MS), is currently the favored instrumental technique for pharmaceutical bioanalysis. However, sample preparation is needed before the LC-MS. Sample preparation may be the dilution of a sample that is typical of urine samples; or Protein Precipitation (PP), Liquid-Liquid Extraction (LLE), Solid-Phase Extraction (SPE). The preparation of the sample aims to make it consistent with the LC-MS system. This occurrence includes removing proteins to prevent contamination of the instrument and removing matrix components that could cause ion suppression, such as phospholipids.

LC–MS-based bioanalytical methods primarily use PP, LLE, or SPE for sample preparation. Since current methods are rooted in these proven sample preparation techniques, which have been developed, perfected, and tested over a long period, acceptance and implementation of new techniques is slow. On the contrary, in scientific literature, sample preparation is an active area of research and development, and micro-extraction is a passionate subject.

In SPME, a thin needle generally coated with Polydimethylsiloxane (PDMS) is placed in the sample solution or headspace, and the target analytes are transferred to this coating. In the next step, the operator or auto-injector inserts the needle into the heated Gas Chromatography (GC) injector. The target analytes thermally desorb and move to the GC column. Just a few years after its release, SPME became commercially available. Since its launch, more than 13,000 SPME-related research papers have appeared, and today scientists are increasingly implementing SPME for routine applications.

Liquid-phase microextraction (LPME) was developed in parallel to SPME. Conceptually, LPME is similar to SPME, except in the former, the extraction process consists of a few microliters of the aqueous solution or organic solvent. Technical structures are referred to as Single-Drop Micro-Extraction (SDME). From SDME, LPME has grown into alternative technological formats like Dispersive Liquid-Liquid Micro-Extraction (DLLME), Hollow-Fiber Liquid-Phase Micro-Extraction (HF-LPME), Dispersive Liquid-Liquid Micro-Extraction Centered on Floating Organic Droplet Solidification (DLLME-SFO), and others.

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