Why would I dare put forth such a question? Perhaps because formaldehyde is the classic preservative used in embalming solutions, due to its ability to fix tissue by irreversibly connecting a primary amine group in a protein molecule with a nearby nitrogen in a protein or DNA molecule. AND\u2026 it also just happens to be one of the three most important volatile organic compounds (VOCs) typically measured at ambient concentrations with 2,4-dinitrophenylhydrazine (DNPH)-coated solid sorbents (i.e., U.S. Environmental Protection Agency\u2019s (EPA) Compendium Method TO-11A). AND\u2026 despite formaldehyde\u2019s ubiquitous nature and thereby concurrent role in multiple arenas (environmental impact, human health, atmospheric chemistry, etc\u2026), DNPH-based methods have several significant shortcomings for measuring formaldehyde. A couple of weeks ago, I hopefully whetted your appetite with the promise of elucidating some of these shortcomings, so here we go\u2026<\/p>\n\n\n\n
It has been known for the past two decades that ozone – another ubiquitous constituent in the atmosphere – interferes with formaldehyde measurements made using DNPH-coated solid sorbents (Achatz et al., 1999). In an attempt to keep this blog as brief as possible, I will not cover the mechanism behind this; however, Achatz et al., 1999 is an excellent resource. Fortunately, the ozone interference may be reduced or alleviated with the use of upstream copper oxide- (Helmig, 1997) or potassium iodide-coated (Possanzini and DiPalo, 1999) denuders or scrubbers. Even better for you (the end-user) is the fact that these remediation strategies are formally addressed in the U.S. EPA\u2019s Compendium Method TO-11A (U.S. EPA, 1999a); and the major DNPH-coated cartridge vendors offer said scrubbers. Oddly enough, as a result of this it appears that most end-users I have polled are aware of the ozone \u201csituation\u201d.<\/p>\n\n\n\n
\u00a0However, a much lesser known difficulty associated with measuring formaldehyde using DNPH-coated solid sorbents is that nitrogen dioxide (NO2<\/sub>) reacts with DNPH to form 2,4-dinitrophenylazide (DNPA) (Karst et al., 1993). As the figure below illustrates, DNPA and the formaldehyde-DNP-hydrazone have similar chromatographic properties. This may result in a high formaldehyde concentration estimate using DNPH-based methods. It gets worse though\u2026 not only is NO2<\/sub>\u00a0a ubiquitous atmospheric pollutant (Hesterberg et al., 2009), but this problem is compounded by the fact that an upstream ozone scrubber (recall the aforementioned ozone situation) can oxidize NO to NO2\u00a0<\/sub>(Tang et al., 2004).<\/p>\n\n\n