Back to Basics
When it comes to sample prep, simple analytical ideas may prove more effective than expensive solutions.
José Manuel Florêncio Nogueira |
Over the past three decades, a huge number of analytical solutions have been proposed for sample preparation in combination with chromatographic or hyphenated techniques. The complexity of many matrices, as well as the trace levels found in the samples, gave rise to what appeared to be novel ideas and modern concepts, most of them in compliance with the green analytical chemistry (GAC) principles. Good examples of well-established sample enrichment techniques are solid phase microextraction (SPME) and stir-bar sorptive extraction (SBSE), introduced around 25 and 15 years ago, respectively (1).
Although these miniaturized passive sampling techniques present outstanding analytical advantages in manipulation, simplicity and sensitivity, they have several limitations. For instance, SPME is mainly associated with gas chromatography (GC) and the fibers involved are fragile and expensive, especially if dedicated to routine work. SBSE is also a costly approach in combination with GC, since a thermal desorption unit is required to desorb the analytes. Furthermore, SBSE was designed with the polydimethylsiloxane phase and, although it has excellent enrichment capacity and thermal stability, it cannot microextract the majority of polar compounds. Finally, both analytical devices were intended to be re-used, which creates difficulties, particularly if the back-extraction stage is performed through liquid desorption (LD), which requires several steps that are neither user-friendly nor compatible with routine analysis.
In the meantime, many other solutions have been suggested for routine work, including automated systems that make sampling, agitation, temperature control and derivatization very easy. Nevertheless, these sophisticated systems are useless in certain circumstances, simply because they are beyond the reach of many laboratory budgets, especially in developing countries. Therefore, we need new microextraction devices for sample prep that combine simplicity, ease of use, low costs, GAC principles and suitability for routine work.
Particularly in resource-poor settings, there is a clear need to focus on using resources that are available in the lab, rather than requiring that users rush out to buy expensive sample preparation supplies or equipment. Recently, we introduced ‘bar adsorptive microextraction’ (BAµE) as a novel passive sample enrichment technique that presents several advantages over previous methods (2)(3).
First, the analytical devices involved can be easily and quickly made in the lab, with very cheap materials. Second, they can be used by anybody, since the extraction stage is performed through agitation without any special requirements – it simply employs the ‘floating sampling technology’ concept. Third, it can be combined with conventional GC or HPLC systems, using a very simple back-extraction procedure that follows the GAC principles. Fourth, it is compatible with current GC and HPLC auto-samplers, which allows routine work without any instrumental investment.
In short, our new cost-effective and disposable BAµE device has a single LD step for the back-extraction stage, and uses only a few microliters of suitable solvents in glass vial inserts which, after sealing, are ready for instrumental analysis using conventional auto-sampler systems.
I believe that if simple, low-cost ideas like this could be implemented in analytical labs all over the world, most of the expensive solutions proposed by analytical instrument companies would be redundant. For the large number of labs worldwide without a huge budget, cheap but effective solutions are needed – and that might mean moving away from commercial pressures and influence.
- JMF Nogueira, TrAC, 71, 214–223 (2015).
- JMF Nogueira, Anal Chim Acta, 757, 1–10 (2012).
- NR Neng, ARM Silva, JMF Nogueira, J Chromatogr A, 1217, 7303–7310 (2010).