From sample prep to low detection levels to automation, environmental analysis provides unique challenges for analytical chemists. Participants in this Technology Forum are Kory Kelly of Phenomenex (Torrance, California), and LCGC Editorial Advisory Board member Pat Sandra of the Research Institute of Chromatography (Kortrijk, Belgium).
Are there still challenges in environmental analysis?
Kelly: Environmental labs continually face challenges as customers and regulations strive for lower limits of detection. Even with recent advances in detector technologies, achieving the high-sensitivity demands becomes a stretch for some compounds. Improving sample extraction efficiencies and cleanup techniques can help improve detection limits, but some analytes are still not being analyzed using appropriate techniques to give the most accurate results. Determining what these compounds are and the appropriate techniques to use is one challenge that faces environmental labs today, even though some may not realize it.
Sandra: There are indeed several challenges remaining in environmental analysis. These challenges can be divided into three classes:
First, some guidelines or directives impose extremely low maximum levels for certain compounds. These values are often based on extrapolated toxicological data and eventually some analytical data obtained in a (nonroutine, atypical) research lab. A good example is the EU directive on tributyl tin (TBT). According to EU directive 2008/105/EC, the quality standard for surface water is 0.0002 µg/L or 200 pg/L. Consequently a lab needs a method that is able to detect in a correct way (sufficient accuracy, precision, specificity, and so forth) TBT at 50 pg/L. These levels can be obtained on sophisticated equipment (for example, a gas chromatography–inductively coupled plasma–mass spectrometry [GC–ICP-MS] system) and even some literature references are available. However, these methods are not at all applicable in a routine environment. In the case of TBT, we have experienced lots of problems with contamination, even from reagents that are specified in the literature references. Consequently, these measurements cannot be performed on a large scale in routine labs and one can question published quantitative data, especially at these ultratrace levels.
Also, for less challenging levels, the contamination problem can occur. Typical cases here are phthalate analysis, dibutyltin analysis, and bisphenol A analysis. Limits of detection are not a problem, but even using published or normalized methods, problems with contamination are often underestimated, so that published values are questionable. It is therefore of high importance that regulating bodies would consider state-of-the-art sample preparation techniques whereby miniaturization, automation, and solvent reduction are possible. Still too often, official methods (probably in an attempt to be “universally applicable”) implement the use of lots of glassware (volumetric flasks, separation funnels, evaporation steps), large amounts of solvent (often the most important source of contamination) and lots of analytical steps. The general rule should be the less glassware used, the lower the amount of solvent used, and the fewer steps, the lower the risk of contamination. This should be kept in mind during method development.
Finally, labs are also looking for automation and high-throughput methods. In their quest for these methods, often the performance of the method is a trade-off. For this reason, it absolutely necessary that these methods are either considered as screening methods (with clear specification of limits of detection, accuracy, and so forth) or that the methods are validated and perform equally to the standard methods.
What special considerations are required for sample preparation for environmental analysis?
Kelly: Extraction efficiencies for widely varying samples (the variation of physical properties of analytes as well as matrices), effectiveness of sample cleanup, and analyte stability are special considerations for sample preparation in environmental analysis. But this has always been the case. It is very difficult to create an extraction and analysis method where every compound in a wide group of analytes is suited for the chromatographic technique, detector chosen, and the same extraction and cleanup techniques.
Sandra: In line with the above, the key words are solvent reduction, miniaturization, and automation. Since instruments (especially MS detectors) are more sensitive, sample amount can be reduced and extraction methods with reduced solvent consumption such as solid-phase microextraction (SPME), stir-bar sorptive extraction (SBSE), or solid-phase extraction (SPE) can be used, resulting in equal (or even better) sensitivity.
Have there been new developments in air monitoring and other sampling techniques?
Kelly: More focus is being given to air analysis recently with an emphasis on real-time monitoring. Some of the analytes may be the same, but more attention is being focused on getting data as pollutants are emitted, getting lower limits of detection, and ensuring the accuracy of those results.