When assessing the inhalation toxicity of diverse inhalable substances, a first step is accurate quantitative analysis. In this study, we developed a method for the quantitative analysis of methylisothiazolinone (MIT) and methylchloroisothiazolinone (CMIT), main components in humidifier disinfectants. A simple thermal desorption (TD) method was used to analyze the CMIT/MIT. Using this method, sample loss during aerosolization was minimized compared with other more complicated pretreatment methods, like solvent absorption and extraction (SV). The results of the TD and SV methods were compared to determine the optimal analytical system for CMIT/MIT analysis. In both methods, the concentration of MIT increased systematically with increasing the CMIT/MIT aerosol concentration (R2 > 0.98). The MIT contents in the aerosol given by the two analytical methods were somewhat similar (MIT content = 1.52% (sample solution), 1.43% (TD) and 1.18% (SV)). In contrast, the measured CMIT content in the aerosol was different depending on the type of pretreatment used. The CMIT content was 2.90% for the TD method, while that for the solvent method recorded 0.75% (CMIT content of the sample solution = 4.66%). We confirmed that the sample loss of the CMIT with high reactivity occurred in the complicated sampling and pretreatment steps of the SV method.

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The quantitative analysis of target substances is an important part of assessing the toxicity of diverse materials. Usually, the quantitation of target compounds is conducted by instrumental analysis such as chromatography and capillary electrophoresis. If solvents are used in the pretreatment step of the target analyte quantification, it would be crucial to examine the solvent effect on the quantitative analysis. Therefore, in this study, we assessed the solvent effects using four different solvents (methanol, hexane, phosphate buffered saline (PBS), and dimethyl sulfoxide (DMSO)) and three toxic compounds (benzene, toluene, and methylisothiazolinone (MIT)). Liquid working standards containing the toxic compounds were prepared by dilution with each solvent and analyzed by gas chromatography-mass spectrometry (GC-MS). As a result, we found that the response factor (RF) values of the target analytes were different, depending on the solvent types. In particular, benzene and toluene exhibited their highest RF values (33,674 ng−1 and 78,604 ng−1, respectively) in hexane, while the RF value of MIT was the highest (9,067 ng−1) in PBS. Considering the correlation (R2) and relative standard deviation (RSD) values, all target analytes showed fairly good values (R2 > 0.99 and RSD < 10%) in methanol and DMSO. In contrast, low R2 (0.0562) and high RSD (10.6%) values of MIT were detected in hexane, while benzene and toluene exhibited relatively low R2 and high RSD values in PBS (mean R2 = 0.9892 ± 0.0146 and mean RSD = 13.3 ± 4.1%). Based on these findings, we concluded that the results and reliability of the quantitative analysis change depending on the analyte and solvent types. Therefore, in order to accurately assess the toxicity of target compounds, reliable analytical data should be obtained, preferentially by considering the solvent types.

Diverse harmful compounds can be emitted during the heating of tobacco sticks for heated tobacco products (HTPs). In this study, the generation of harmful compounds from the filter, instead of tobacco in tobacco sticks, was confirmed. The heat of a heated tobacco product device can be transferred to the tobacco stick filter, resulting in the generation of harmful compounds from the heated filter. Since the heating materials (tobacco consumable) of the tobacco sticks evaluated in this study were different depending on the brand, the harmful compounds emitted from the heated tobacco stick filters were examined by focusing on the carbonyl compounds, using three different tobacco stick parts. Acetaldehyde and propionaldehyde exhibited the highest concentrations in HTP aerosols produced by heating the tobacco consumable (conventional case) (63.5 ± 18.4 µg/stick and 1.71 ± 0.123 µg/stick, respectively). The aerosols produced by heating tobacco stick filters had higher formaldehyde and acrolein concentrations (0.945 ± 0.214 µg/stick and 0.519 ± 0.379 µg/stick) than the aerosols generated from heated tobacco consumable (0.641 ± 0.092 µg/stick and 0.220 ± 0.102 µg/stick). As such, formaldehyde and acrolein were produced by heating small parts of the mouthpiece of a tobacco stick, regardless of the heated tobacco product brand. In addition, acetone was only detected in the aerosols generated from heated filters (0.580 ± 0.305 µg/stick). Thus, safety evaluations of heated tobacco products should include considerations of the harmful compounds generated by heating tobacco stick mouthpieces for heated tobacco products in addition to those found in heated tobacco product aerosols.