Development of a Wipe Sampling Method for o-Phthalaldehyde

1072 

Professional Poster 

P Dunn¹

¹Chubb Environmental Health Laboratory, CROMWELL, CT

Patrick Dunn, CIH  
Chubb Environmental Health Laboratory

In 2018, when the TLV-SL concept was first introduced we did research into what methods might already be available to address this new class of TLV. For o-Phthalaldehyde we determined that development of a new method would be our best avenue. To that end, we developed a standard protocol for developing wipe based methods, along with a specific method for the proper collection, preservation and analysis of o-Phthalaldehyde. We wanted to maximize our efforts, and attempted to include all common aldehydes plus o-Phthalaldehyde performed under EPA TO-11 method. This session will detail our method development process along with the final recommendation on how to collect aldehydes using a wipe sampling method.

In 2018, the ACGIH published the TLV book containing the first Notice of Intended Change (NIC) adding the new surface wipe limit to be known as a Threshold Limit Value - Surface Limit (TLV-SL). In that same publication, o-Phthaldehyde was added to the NIC list with the new "SL" designation at a limit of 0.025 mg/100cm2. What made this TLV of interest to our community was that this compound was one of the first to receive the new Threshold Limit Value – Surface Limit (TLV-SL) designation. The purpose of this new genre of exposure assessment was to provide guidance on chemical concentrations from work surfaces which may promote adverse effects through dermal exposures. Neither OSHA nor NIOSH have published a method for o-Phthaldehyde sampling by wipe method (or in air for that matter). An article published in the Journal of Environmental Monitoring listed two wipe based methods for o-Phthaldehyde. One had a detection limit that was too high. The second method used toxic chemicals and an expensive fluorometer for preparing and reading wipe samples in the field.

OSHA 64 method for Glutaraldehyde was the basis for our development of a wipe sampling method. This method used a 2,4-dinitrophenylhydrazine (DNPH) treated glass fiber filter for sample collection. Given that both glutaraldehyde and o-PA were similarly nonvolatile aldehydes, this seemed a good place to start. The method called for the use of high performance liquid chromatography, UV detection with a common C-18 based column for separation. DNPH is listed in many validated methods for collection and analysis of a variety of aldehydes. However, there are some aldehydes which have additional functional groups which allow them to undergo additional side reactions with DNPH. O-PA is one such aldehyde. An effort was undertaken to find a DNPH solution that would provide the three key elements we were looking for in an extraction solution: a) o-PA would derive fully to a stable dimer form; b) the reaction would be complete inside of an hour; and c) once the reaction was complete, a precipitate would not appear. The extraction solution investigation results were: 1) 100% Acetonitrile, the o-PA secondary derivative form was insoluble; 2) 70/30 DMSO/ACN, the o-PA secondary fell out of solution within 2 days; and 3) 99/1 DMSO/H3PO4, the o-PA remains stable and moves all the way to the final derivative.

Next we searched for a wetting solution that would minimize the potential exposure hazard when used in the field (and for shipping). Methanol was selected because it provided better solubility than water and is less toxic than acetonitrile. The final step was to work on a protocol for spiking known amounts on a surface and to collect samples using the glass fiber filter wetted with methanol. A Teflon surface was selected as our spiking surface due to its inert behavior along with the ability to be repeatedly cleaned and used again without cross-contamination. The mat used was approximately 12in x 15in. A 100 cm2 template was used to demark the test wipe areas. Two spiking methods were used to deliver o-PA to the test surface. One, amounts of crystalline o-PA were weighed out and placed onto the test surface. The second method had known amounts of o-PA dissolved in acetonitrile and delivered by microsyringe onto the test surface. Replicates were taken using a glass fiber filter wetted with methanol. Result recoveries for both spiking methods were greater than 90%.

Our original pathway looking at the use of DNPH treated filters as a wipe media did not work well for o-PA. Success was found using an untreated 37 mm glass fiber filter wetted with methanol to improve solubility and retention of particulate/crystalline based o-PA. Advantages of this solution were decreased use of hazardous chemicals in the field, along with reduced potential damage to surfaces. Samples were shown to be stable for 5 days even at room temperature. Analytically, the secondary reaction of o-Phthalaldehyde was best controlled using a solution of 99/1 DMSO/H3PO4. The final derivative remained in solution and was stable.

Sampling and Analysis

Exposure Assessment Strategies