LC-MS today and tomorrow

Liquid chromatography-mass spectrometry (LC-MS) is a highly sensitive and specific analytical chemistry technique that is very commonly used in pharmacokinetic studies of new chemical entities. LC-MS has largely supplanted older techniques such as LC-UV for in vivo quantitation and is now the most frequently used technique in the field of bioanalysis. Across the history of LC-MS/MS quantitation specifically (now approaching 20 years in the mass market), the initial advantages were in improved specificity — leading to shorter LC run times — and improved sensitivity. The improvements in specificity facilitated analysis of many more samples in a short time provided that the necessary capital expenditures were made.

Though the most common method of bioanalysis, a number of challenges exist with LC-MS quantitation, including:

• Technology: the role and acceptance of dried blood spot (DBS) analysis remains unclear because of the limited history of this technique in bioanalysis.

• Cost management: solid phase extraction cartridges and plates or DBS cards are expensive, and personnel costs vary widely across locations.
• Time management: time efficiency must be achieved throughout the analysis chain. This includes a reduction in the time needed for methods development and validation, transport time for materials (and especially across borders), and time required for data processing, management and release.

In terms of overall bioanalysis, the greatest unknown presently is the role that DBS analysis will play in this field. The limited sample volume in DBS is a challenge for assay sensitivity, particularly for assays targeting the lower pg/mL concentration range. In addition, there are new and different challenges for each analyte with respect to the sample card and card coating types.

Innovations
Innovations to improve the sensitivity of LC-MS/MS are yielding continued benefits. Ever-greater sensitivity helps minimise the cleanup needs of sample preparation; samples can be minimally cleaned, then diluted for analysis. However, for analytes such as peptides, better solutions to sensitivity problems are still needed.

An alternative technology that we are exploring is the use of LC with High Resolution Mass Spectrometry (HRMS). This technique can enhance both sensitivity and specificity for certain types of analytes (e.g., peptides, steroids) and may evolve to be a critical quantitation tool within the next few years. Early uses for LC-HRMS may be in drug discovery, where bioanalysis can now capture quantitation and metabolite screening in a single simple analysis. If harnessed, this greater access to information could be transformative to discovery and lead optimisation programmes.

The equipment to support high-throughput for DBS analysis is still in the earliest stages of development and implementation. If efficient solutions are developed for sample collection and management, card sampling and elution of analytes from the dried matrix, the inherent advantages of DBS, such as reduction in subject inconvenience and serial sampling from animal models, can reach fruition. Rapid evolution of the DBS technique and tools is expected as adoption and acceptance becomes more widespread.

www.pharmanet.com