Editorial
There Is No Analysis Without Sampling
S
ampling is where the rubber meets the road for all applications of analytical chemistry methods, and as such it is a continuing Frontier of our discipline. Each area of application presents its own challenge to the analyst. Different samples—such as foodstuffs, pharmaceuticals, and a host of consumer products; waste and natural streams; vapors in the workplace, home, and atmosphere; and living biological systems present different sampling parameters, such as matrix heterogeneity, constituent concentrations and transport dynamics, fragility to generation of artifacts by the sampling method itself and size of the space to be sampled The analyst ideally wishes to quickly and inexpensively obtain a representative bite of the analyte in a concentrated form free from other species that interfere with the analyte's subsequent measurement This journal has in the past several vears reported a steady stream of innovations in sampling and it seems appropriate to recognize and applaud this progress and to point to some especially significant aspects Analytical chemists no longer regard sampling as the simple procurement of a representative piece of the material to be quantitatively dissected. Rather, it has become an integrated process in which desired analyte(s) are transposed from the original, complex, heterogenous matrix into a small-volume phase that is subsequently induced to give up the preconcentrated analyte(s) to a measuring instrument. These steps contain opportunities for selectivity and analytical simplification in what is removed from the original matrix and subsequently presented for measurement. A myriad of reports have miiked these opportunities. For example, in head-space techniques, volatiie analyte(s) over complex, messy matrices can be partitioned into thin polymeric phases and then thermally released into measuring systems like GC or GC/MS in a procedure termed solid-phase microextraction. Analytes can also be extracted into droplets and released into chromatographic or atomic emission systems. The typical feature in these innovations is the small preconcentrating volume of the extracting phase and its compatibility with
the measuring step. Older digestion approaches used for nonvolatile and not readily dissoluble sample matrices have been supplanted by the energetic persuasion of a laser pulse followed by atomic emission or mass spectrometric measurement Advances such as these promise important benefits to a host of analytical applications. Some even tougher sampling tasks are just beginning to yield to the analytical chemist Individual sampling of physically small matrices, such as aerosol particles, raindrops, and grain structures in heterogenous solids, is especially difficult. For aerosols and other small airborne particles, the numerous significant unknowns associated with size and other analytical heterogeneities necessitates separating the individual particle from its neighbors. Aerodynamic fractionation of particles with impactors has reached a sophisticated level, but even more exciting are the possibilities raised by laser ablation of individual particles still airborne. The laser is also an important weapon in space-resolved ablation sampling of heterogeneous solid surfaces Biological structures, such as the volume inside a single cell or the cell membrane itself, offer additional parameters for the sampler—being not only tiny but extremely complex and chemically fragile. Central progress here is in the evolution of microscopic probes in which the sampling device is miniaturized to the dimensions of the biological structure. There are many more advances in sampling than I can mention in this salute to progress, and I apologize to those whose innovations I have not touched upon. Research in this terrifically important facet of analytical chemistry is vibrant and alive. Nonetheless, many needs and opportunities remain, and I'll comment on some next month. In the meantime, let's thank those who work on analytical sampling for their crucial synergy with progress in measurement methods in meeting today's needs for analytical applications.
Analytical Chemistry News & Features, May 1, 1997 2 6 9 A
