O-phthalaldehyde (OPA) is a high-level disinfectant commonly used, for example, for sterilization of heat-sensitive medical instruments; it demonstrates effective microbicidal activity against a wide range of microorganisms (including mycobacteria, gramnegative bacteria, and spores). On the International Space Station (ISS), to achieve thermal control and maintain components at acceptable temperatures, systems that produce waste heat need to have that heat transferred from the ISS to space. To accomplish this, the ISS has an Internal Active Thermal Control System (IATCS) — a water-based system that works in conjunction with the EATCS (External ATCS), an ammoniabased system — to facilitate this heat transfer process.

The IATCS, which consists of loops that circulate water through the interior to collect the excess heat, is responsible for the removal of heat loads from payload and system racks. In the IATCS coolant, to prevent microbial negative impacts to coolant flow, heat transfer, and corrosion, an OPA water solution is used as a high-level disinfectant to effectively inhibit the growth and recovery of viable microorganisms; this is because accumulation of microorganisms on surfaces could result in IATCS material degradation. If the IATC is damaged, functionality of system racks could be adversely affected, which in turn could ultimately affect crew health and safety. Therefore, the concentration of the disinfectant OPA in the coolant fluid is critical to maintaining proper function of IATCS. The method previously used for developing, analyzing, and validating the OPA concentration had been a proprietary process, which recently became unavailable to NASA. A subsequent literature search only provided technical information on a method that was both labor intensive and involved using hazardous materials (hydrazine dissolved in concentrated sulfuric acid). Therefore, to address this critical need for ISS, an analytical process by which a known concentration of OPA could be verified with precision and accuracy was developed. This involved creating a process to quantitate OPA in water-based liquids using a high-pressure liquid chromatography (HPLC) combined with post-column derivatization.

To do this, National Institute of Standards and Technology (NIST) traceable EPA method 547 for quantitating glyphosate concentration in water, which uses a HPLC method that uses OPA to convert glyphosate in a post-column reactor into a compound that can be more readily detected, was reverse engineered. By reversing the premise of this process, to determine OPA as the quantitated analyte and glyphosate as the excess derivatization agent, OPA was quantitated. Calibrations were established, and initial demonstration of proficiency studies (IDOPs) and a method detection limit (MDL) study were analyzed simultaneously alongside one another over three instrument runs to demonstrate precision and accuracy. Method detection limit and linear dynamic range were established. OPA peaks were observed on the HPLC, and steps were repeated for accuracy and repeatability. This SSC-developed and validated, simple, inexpensive, traceable process to analyze OPA, that neither requires hazardous chemicals nor has a hazardous waste stream that is expensive to discard (thereby substantially reducing hazardous chemicals exposure and potential hazard health effects), offers a new, highly effective, low-cost HPLC technique from existing identified processes.

This work was done by Eugene Al Watkins, Danelle Dees, and Tabatha Butler of A2Research for Stennis Space Center. For more information, contact Eugene Al Watkins at 228-688-1447, or A2Research, Building 8110, Room 103, Stennis Space Center, Stennis, MS 39529. Refer to SSC-00448.

NASA Tech Briefs Magazine

This article first appeared in the October, 2015 issue of NASA Tech Briefs Magazine.

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