Trimethylsilanol (TMSOH) can cause damage to surfaces of scanner lenses in the semiconductor industry, and there is a critical need to measure and control airborne TMSOH concentrations. This study develops a thermal desorption (TD)-gas chromatography (GC)-mass spectrometry (MS) method for measuring trace-level TMSOH in occupational indoor air. Laboratory method optimization obtained best performance when using dual-bed tube configuration (100？mg of Tenax TA followed by 100？mg of Carboxen 569), n-decane as a solvent, and a TD temperature of 300°C. The optimized method demonstrated high recovery (87%), satisfactory precision (<15% for spiked amounts exceeding 1？ng), good linearity ( ), a wide dynamic mass range (up to 500？ng), low method detection limit (2.8？ng？ for a 20-L sample), and negligible losses for 3-4-day storage. The field study showed performance comparable to that in laboratory and yielded first measurements of TMSOH, ranging from 1.02 to 27.30？ , in the semiconductor industry. We suggested future development of real-time monitoring techniques for TMSOH and other siloxanes for better maintenance and control of scanner lens in semiconductor wafer manufacturing. 1. Introduction Trimethylsilanol (TMSOH, CAS No. 1066-40-6) in industrial sectors has gained wide attention due to the widespread use of silicon materials and their detrimental effects on equipments and products [1]. TMSOH is a silanol but often is considered to belong to the siloxane group. It is the most volatile siloxane with a vapor pressure of 73.9？mmHg at 25°C [2]. Siloxanes are a family of silicon containing organic compounds that are widely used in manufacture of commercial and consumer products, for example, detergents, deodorants, and cosmetics [3, 4]. Siloxanes are considered safe to the general population and available toxicological studies target octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6); thus, no inhalation toxicity data are available for TMSOH. Limited oral and skin exposure studies show that TMSOH causes nervous system depression and anesthesia at high doses [5]. Oral toxicity tests determined a no observable effects limit of 160？mg/kg/day in rats [6]. The U.S. Occupational Safety & Health Administration has not set exposure limits for TMSOH [7]. The U.S. National Academies have set 65？mg/m3 and 32？mg/m3 as 24-hour and long-term spacecraft maximum allowable concentrations for TMSOH, respectively [5]. The U.S. Environmental Protection Agency (EPA) is proposing a chemical action plan for siloxanes to
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