BPE-DNPH: A More Effective Device for Sampling Airborne Carbonyls Under High Humidity Conditions

By: Shigehisa Uchiyama Jamie Desorcie and Kristen Schultz, Reporter US Volume 28.4

Shigehisa Uchiyama1, Jamie Desorcie, and Kristen Schultz kristen.schultz@sial.com
1. National Institute of Public Health
2-3-6, Minami, Wako City, Saitama 351-0197, Japan

Derivatization with 2,4-dinitrophenylhydrazine (DNPH), followed by HPLC analysis, is a widely used selective and sensitive method for the measurement of carbonyl compounds in air (Figure 1). However, ozone is a known chemical interference of the method.

Figure 1. Measurement of Carbonyl Compounds in Air

Ozone interferes negatively at high concentrations by reacting with DNPH and its carbonyl derivatives (2,4-DNPhydrazones) that are formed in the sampling cartridge.

Ozone scrubbing cartridges are available that contain potassium iodide. These are placed before the DNPH cartridge in the airsampling train and trap ozone before it can interfere with the reaction between DNPH and carbonyl compounds. However, potassium iodide can become wetted under high humidity conditions. The wetted potassium iodide can trap carbonyl compounds before they reach the DNPH sampler. In addition, wet potassium iodide can migrate into the DNPH sampler and generate unknown compounds.

An alternative ozone trap to hydroscopic potassium iodide is 1,2-bis(2-pyridyl)ethylene (2-BPE). 2-BPE is unaffected by atmospheric moisture and removes ozone via the formation of pyridine-2-aldehyde as outlined in Figure 2.

Figure 2. 2-BPE is Unaffected by Atmospheric Moisture and Removes Ozone via the Formation of Pyridine-2-aldehyde

The BPE-DNPH sampler is a 2-bed cartridge consisting of silica particles impregnated with 2-BPE and DNPH (Figure 3). Air is first drawn through the 2-BPE bed, which can trap up to 0.24 mg ozone. Airborne carbonyls pass unimpeded through the 2-BPE bed and are trapped in the second bed by the DNPH-coated silica particles.

Figure 3. BPE-DNPH Cartridge

The effectiveness of 2-BPE as an ozone scrubber, particularly under high humidity conditions, is demonstrated by the data presented in Table 1 (Reference 1). Ambient air was sampled during various time periods during 2009 in Chiba City, Japan. Two sampling devices were used – a BPE-DNPH cartridge and a conventional DNPH cartridge coupled to a potassium iodide (KI) ozone scrubber. Formaldehyde and acetaldehyde concentrations were measured using DNPH protected by each ozone-scrubbing material. Average ozone concentration, reported by a local air monitoring station, is also listed.

Table 1. Concentrations of Formaldehyde and Acetaldehyde Measured in Ambient Air Collected by a BPE-DNPH Cartridge and a DNPH Cartridge Coupled to a KI Ozone Scrubber

When the relative humidity was close to 50% (February 21-22 and March 20-21), similar concentrations of formaldehyde and acetaldehyde were measured using either 2-BPE or KI to scrub ozone. Alternatively, much higher concentrations of formaldehyde and acetaldehyde are measured using the BPE-DNPH cartridge when the relative humidity is above 90% (April 25-26 and May 30-31). It is believed that wet potassium iodide acts as a trap for formaldehyde and acetaldehyde and prevents much of these materials from reaching the DNPH sampling reagent. In addition, potassium iodide was observed to migrate into the DNPH cartridge, which resulted in a color change of yellow to reddish brown. This is depicted in the photographs in Figure 4.

Figure 4. Appearance of a DNPH Cartridge, a KI Ozone Scrubber Coupled to a DNPH Cartridge and a Dual-Bed BPE-DNPH Cartridge Following Exposure to High Humidity Air (>90% RH)

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Conclusions

The dual-bed BPE-DNPH cartridge is preferred over a DNPH cartridge coupled to a potassium iodide ozone scrubber for sampling carbonyls in high humidity, ambient air. Unlike wetted potassium iodide, 2-BPE does not trap carbonyl compounds before they are able to reach the DNPH sampling medium. Also, removal of KI from the sampling train eliminates the possibility of KI migration to the DNPH bed where it may interfere with the carbonyl-DNPH derivatization reaction.

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References

  1. Uchiyama, S., Naito, S., Matsumoto, M., Inaba, Y., Kunugita, N. Anal. Chem. 2009, 81, 6552.

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