In-injection port thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) allows for analysis for > 130 non-polar organic compounds on small quartz-fiber filter samples without extraction chemicals. TD-GC/MS has been applied to samples from long-term U.S. networks since it is cost effective and less labor intensive. However, analysis of large numbers of samples results in sensitivity reductions over time. Instrument sensitivity and reproducibility were examined after 100, 200, and 500 sample analyses. Analyses of standards between batches of heavily loaded samples from China and Japan showed signal decreases of 28-78% for major organic classes. In the GC injection port, residues can accumulate on the gold-plated seal resulting in analyte adsorption as well as elevating signal background. Decreases in signal response were 28-43% for n-alkanes, 33-45% for hopanes and steranes, 28-56% for PAHs, and 38-78% for phthalates when the gold-plated seal was not replaced after 500 TD-GC/MS sample analyses. Limits of detection (LODs) also increased by 14-76% for the targeted non-polar organic compounds. Residues trapped in the capillary column head can cause peak broadening and overlap. The GC/MS system, including the injection port and gold seal, the column head (where the eluted sample is pre-concentrated), and the ion source should be cleaned after every batch of 50-100 samples. (C) 2010 Elsevier Ltd. All rights reserved.