Analytical laboratories using techniques such as LC-MS/MS or GC-MS are continuously searching for ways to increase throughput, reduce turnaround times and lower costs. Sample prep is often an underestimated component in this process, but is a critical step that removes matrix interferences, concentrates samples, and also protects expensive analytical instrumentation.
This gives high performance analytical instrumentation the best possible chance of consistently delivering accurate results with high sensitivity. Not only that, robust sample prep will reduce instrument downtime and minimize the need for re-runs. We can first look at the challenges of sample prep and assess what can be done to improve efficiency.
Why sample prep?
Taking LC-MS/MS analysis of an analyte in a biofluid as an example, sample prep will:
- remove proteins and other sample components that could precipitate when injected into the LC mobile phase and clog the column.
- prepare the sample for the chromatographic separation, by removing interfering substances and enabling a change to a buffer that ensures high performance separation.
- deplete the biological matrix to increase the analyte-to-matrix ratio to improve the precision, accuracy, and reproducibility of the analytical method; and,
- reduce exposure of expensive analytical equipment to sample components that impact instrument stability.
Workflows are so complicated!
Sample preparation methods are as diverse as sample types and the analytes to be determined. For most biological matrices, the focus is on sample clean up and concentration, based on techniques such as solid-phase extraction (SPE), protein precipitation, liquid-liquid extraction (LLE), or supported liquid extraction (SLE). However, complex the sample prep might appear, a thorough analysis of the workflow can lead to a lot of streamlining. Solid-phase extraction, for example, has become especially popular due to the availability of a large range of sorbents and affinity phases that can be incorporated into SPE columns and plates to support high enrichment with good recovery and low consumption of organic solvents.
It takes so much time…
Time is money and as analytical run times becoming shorter and shorter, multiple, laborious steps can make sample preparation a real bottleneck. Indeed, pre-analytical sample preparation and extraction can be the most time-consuming part of an assay.
The need to perform time-consuming and repetitive steps locks up our skilled staff with laborious and boring tasks when they could be more usefully deployed. This adds unnecessary personnel cost to every sample and reduces profitability.
The risk of errors
It’s a fact that bored people get tired and make mistakes, and the risk increases with the complexity of sample preparation. Errors made in sample processing and extraction cannot be corrected, even using the most advanced analytical methods available. The most significant sources of errors in chromatographic analyses tend to be sample processing and operator error.
So why invest in costly sample prep?
We have already mentioned the cost of personnel running laborious sample prep. Attempting to avoid investments in sample prep by sticking with complex and laborious manual operations is false economy. Efficient low-error sample prep means cleaner samples that support robust, reliable analyses and minimal risk of re-runs. Pure samples also protect expensive analytical instruments from contaminants, reducing costly downtime, avoidable maintenance, and cleaning.
But it must have an impact on analyte recovery!
There can be the perception that changes in sample prep will impact analyte recovery and threaten method sensitivity. With the right approach, however, this can be avoided, ensuring that analytes are recovered at a high level in a low background of interfering substances to support sensitive analysis.
The gains to be made by automating sample prep