So what are we to do about all the TO-11A issues? A multi-blog series on airborne carbonyls, part V – THE FINALE!!!

It is time to recap and wrap this series up. In part I I simply highlighted the fact that the sampling and analysis of airborne aldehydes and ketones (carbonyls) with 2,4-dinitrophenylhydrazine (DNPH)-coated solid sorbents (i.e., United States (U.S.) Environmental protection Agency’s (EPA) Compendium Method TO-11A or some derivation thereof (e.g., California Air Resources Board (CARB) Method 1004)) are plagued by several important issues. Specifically, I focused on formaldehyde, acetaldehyde, and acrolein (what I like to term the “big three”), because of their environmental and human health importance.

In part II I covered the short-comings associated with sampling formaldehyde, a known human carcinogen. In case you did not read that blog (not really sure why???), the take away points were as follows:

1. Ozone reacts with DNPH and the formaldehyde-DNP-hydrazone derivative, thereby resulting in possible negative biases.
   • This problem may be alleviated by the use of an ozone scrubber/de-nuder.
2. NO₂ reacts with DNPH to form 2,4-dinitrophenylazide (DNPA), which co-elutes with the formaldehyde-DNP-hydrazone derivative, thereby resulting in possible positive biases.
   • This problem may be alleviated by the use of different chromatographic conditions and/or a diode array detector.
3. NO can be oxidized by ozone scrubbers/de-nuders to form NO₂, which means repeat step 2 above.
4. Most important… the issues associated with ozone have been appropriately addressed in standardized methods and it appears that the majority of the scientific community is therefore cognizant of said problems. HOWEVER, the difficulties associated with NO and NO₂ have not been addressed in any of the standardized methods, and therefore it appears that the majority of the scientific community is un-aware and probably reporting biased data.

In part III I discussed the difficulties associated with sampling acetaldehyde, a probable human carcinogen. The take away message was:

1. DNPH-coated solid sorbents work well for sampling acetaldehyde for short-term sampling durations (i.e., that is on the order of minutes to a few hours).
2. However, acetaldehyde collection efficiencies drop off to ~50% beyond 6 hours of sampling.
   • The reason for this has not been elucidated and more importantly, there currently is no solution for this.
3. This is significant considering that the National Air Toxics Trends Stations (NATTS) and Photochemical Assessment Monitoring Stations (PAMS) are all reporting acetaldehyde concentrations based on 24-hour sampling. Odds are… they are under-reporting the acetaldehyde concentrations.
4. AGAIN… none of the aforementioned is addressed in the standardized methods.

In part IV I discussed the multiple short-comings associated with sampling acrolein, a potent lung and eye irritant. The take away note was:

1. The sampling and analysis of acrolein with DNPH-coated solid sorbents has copious problems.
2. To date… there has not been a method published for sampling acrolein, that has been rigorously tested.
   • I often hear rumors at conferences and through colleagues about methods, which capitalize on “summing the various acrolein” peaks (go back and read part IV for a better understanding). However, I have yet to see any of these methods in the peer-reviewed literature.
   • I am also aware of a manuscript which has gained some recent attention. In shore, the method the authors proposed capitalized on the use of hydroguinone (something I did back in the day sampling acrolein with dansylhydrazine (DNSH) (Herrington et al., 2005)) on a second cartridge for acrolein. I have the following 3 major issues with said method:
     • Who wants to use another cartridge? You already have to use 2 in the presence of ozone… now 3???
     • The method has not been rigorously tested with the use of a gaseous acrolein standard to evaluate collection efficiencies.
     • The method does not address any of the formaldehyde and acetaldehyde issues.

So what are we to do about all the TO-11A issues? Well… I am not saying the method is useless; you can certainly sample formaldehyde and acetaldehyde, but you better make sure you are doing so for only short-term (i.e., a few minutes to a few hours) sampling durations… oh don’t forget your ozone scrubber/denuder in case ozone is present… oh you should also mind your NO and NO₂ concentrations. MAN… that sure seems like a fair amount to be cognizant of just for two compounds. For the record, the issues surrounding the sampling of other carbonyls (my opinion is that they do exist) have not discussed here, because they have not been fully elucidated... YET!

I am of the opinion that we need to start exploring other derivatization agents. I know from personal experience that DNSH performed far better than DNPH. I have also read promising literature on benzylhydroxylamine (BHA). These are just two quick examples of alternatives that do exist. Bottom line, DNPH-coated solid sorbents have been around for over 30 years now. It they are not meeting all of our demands, then perhaps it is time to pursue other avenues. Who knows… maybe there is not a suitable substitute for DNPH? In that case, we need to use the method as is, but at a minimum the standardized methods need to be modified so as to accurately reflect the known limitations.

Lastly, whatever future endeavors researchers choose to explore… I urge them to focus on multi-component methods. Recently, acrolein has been such a hot topic that I have seen far too many methods aimed at collecting just acrolein and the other carbonyl species (which are equally important) have been overlooked.

For more detailed information on all of the aforementioned and any appropriate references, feel free to check out my most recent manuscript (Herrington and Hays, 2012).