An Approach to Quality Control of the Dithiothreitol (DTT) Assay for the Determination of Oxidative Potential of Atmospheric Particulate Matter

The oxidative potential (OP) of airborne particulate matter (PM) has emerged as a promising metric to assess the capacity of particles to induce oxidative stress and related health effects. Thus, ensuring the reliability and comparability of OP measurements is essential for accurate environmental and toxicological assessment. This study aimed to develop and evaluate a quality control approach for the dithiothreitol (DTT) assay used in OP determination. The DTT assay provides an estimation on how harmful PM can be to human health through oxidative stress, relating it to the consumption of DTT during the test period. Two experiments were conducted using the Standard Reference Material (SRM) 1648–Urban Particulate Matter (NIST, USA). The first assessed the effect of trichloroacetic acid (TCA) addition order and the feasibility of using SRM 1648 as a reference material. The second evaluated the stability of the SRM solution over a 63-day period. Statistical analysis (Mann–Whitney test) indicated that the order of TCA addition did not significantly affect OP values (p > 0.05). SRM 1648 solution determination showed high reproducibility (mean DTTₘ = 14.6 ± 2.4 pmol·min−1·µg−1), although a gradual increase in DTT metrics was observed over time, consistent with progressive dissolution. The results support the application of SRM 1648 as a reference material for DTT assay quality control, supporting methodological harmonization in OP determination, provided that a freshly prepared solution is used.