Almost every modern-day method uses recent technology in instrumentation for the detection and quantification of whatever analyte or analytes are of interest. The benefits of today’s systems are very clear: better separations, faster run times, increased sensitivity, and greater ease of use, among many others. Also, many of these techniques must be used because labs are required to follow regulatory or pre-established methods where the analytical technique and method conditions are prescribed. But regulatory agencies or method development labs will employ these methodologies because of the benefits just mentioned.
However, when it comes to preparing samples for that analysis, many labs are still performing these processes manually. Even though instruments are readily available for these procedures, the adoption of these devices is not as common. So, does an instrument for sample preparation modernize and improve methods or is it just a convenience, so other tasks can be accomplished in the laboratory?
One of the main reasons for doing sample prep is to obtain a truly representative sample of what is in the matrix being analyzed. Ideally, recovery should be 100%, but it is not realistic to expect this for every sample. Most methods have a range for acceptable recovery, depending on the matrix and analytes. Some compounds are difficult to extract and may tend to come out low, while others may be enhanced by matrix effects or method bias and will come out over 100%. Using PFAS as an example, regulatory methods for drinking water — such as US EPA 537.1 or EPA 533 — demand recovery be between 70 and 130%. There is also a reproducibility requirement of <20% RSD.
Automation helps recoveries because it helps bring consistency to the process. Preparations done manually are subject to many variations. In the case of solid-phase extraction when done manually, volumes applied to cartridges can be slightly different due to the device used to add liquid to the SPE cartridges; elution rates may change from cartridge to cartridge due either to vacuum pressure differences across a manifold or cartridge valves being set slightly differently. Many methods, will have an optimal flow rate for elution or loading, like US EPA 537.1, which calls for loading the sample 10 to 15 mL/min. This is very difficult to judge by just looking. Thermo Fisher Scientific application note on EPA 537.1, using the AutoTrace 280 PFAS™, shows excellent recoveries (ranging between 84% and 123%) and reproducibility (9.9% RSD is the highest) for all the target PFAS compounds, which is well within method requirements.
Error reduction is one of the biggest benefits an automated system brings to the sample prep process. Almost all labs state that when an error occurs, the most common cause is in the sample preparation process. Doing sample prep manually is prone to errors because of the multiple, sometimes complex steps involved. Unfortunately, detecting errors during the process is very difficult, if it is even possible. Mistakes during sample prep become evident only when an unexpected result is obtained. In some methods, such as unknown screening or other discovery workflows where there is no “expected” result, errors may not even be found. The process for discovering the source of the unusual result is very tedious, time consuming and costly. Using an instrument for sample preparation greatly reduces sources of errors because it will follow the same procedure time after time and can control the steps of the process precisely. This will lower the risk of having to rerun samples, obtain new samples or miss holding times, and will make the lab more productive with a higher confidence in results.
Better technology and improvement of methods are also a huge advantage in using automation for getting your samples ready for analysis. This is especially seen when working with solid samples like soils. Traditional extraction methods like Soxhlet are time consuming, use a lot of solvents and have variations in extraction efficiencies. When an automated system, like the Thermo Scientific™ Dionex™ ASE 350™, is used for the same extraction, it is done much faster with far less solvent used. This is because an instrument can utilize higher temperature and apply pressure to keep the solvent in a liquid form at an elevated temperature. The result is a more efficient extraction, since the solvent is better able to diffuse into the solid sample and extract the compounds of interest, especially when your sample contains multiple compounds of interest such as in the application note for extracting pesticides and persistent organic pollutants. Also, the same benefits previously mentioned — error reduction and constancy — apply here as well.
Is automating your sample prep about convenience? Yes, but there are many other benefits as well!