# Comparison of Water Pretreatment Devices for the Measurement of Polar Odorous Compounds
## 1 Introduction  
A water pretreatment device is an apparatus that can remove only water vapor presented in sample gas in order to improve accurate and reliable sampling and analysis. Interference and loss of analytes occur when samples containing water vapor are taken from the atmosphere [1]. Furthermore, the measuring instruments could be damaged by the remaining water vapor. Water vapor taken with a sample gas could disturb the adsorption capacity of adsorbents, destabilize the baseline of the chromatograph, cause column damage, and change the retention times of sample compounds [2]. It might also clog the transfer line of the instrument or reduce the sensitivity of the measurement process [3]. In terms of detectors, the filament condition could be changed during the operation of a mass spectrometer (MS), which results in response variation [4]. In order to minimize problems caused by water vapors, the U.S. EPA and the Korean Ministry of Environment recommend the use of a water pretreatment device at the fore of the samplingsystem or analyzer. Nafion(r) dryers and coolers were especially recommended according to sampling environment [5; 6; 7; 8; 9]. Nafion(r) dryers are the most common water pretreatment devices. Thus, they have been widely applied to the analytical process of corrosive gases due to their high chemical durability [7]. The Nafion(r) dryer could remove water vapors by water adsorption/desorption through the Nafion(r) membrane [10]. On the other hand, a cooler adopting a Peltier could remove water vapors by reducing the temperature of sampled gases to dew point. Hence, water vapor in air is condensed into its liquid phase when it passes through the temperature-lowered impinger and removed. The water vapor removal of the cooler depends on the surface area and length of an impinger, gas-flow rate, and the material and temperature of the cooling part [11]. Although Nafion(r) dryers have been widely employed as water pretreatment devices, some polar compounds, such as alcohols, aldehydes, ketones, and water soluble esters were found to be removed [12; 13; 14]. [PERSON] et al. [15] found that the heat regeneration of a Nafion(r) dryer depletes and rearranges some hydrocarbons in the sample. In addition, [PERSON] et al. [16] reported that artifact formation could occur for benzene in a Nafion(r) dryer. The U.S. EPA [17] suggested that when the volatile organic compound (VOC) was analyzed using a Nafion(r) dryer as a water pretreatment device, polar compounds were removed with water vapor, and they could not be identified. [PERSON] et al. [18] reported that a Nafion(r) dryer should not be applied for the measurement of low molecular VOCs because contamination might occur in the dryer. In addition, a water pretreatment device should be carefully selected, so that there is no loss of polar VOCs and no introduction of contaminants, because the polar VOC could be lost by a water pretreatment device, including a Nafion(r) dryer [4]. Likewise, many studies [4; 12; 13; 14; 15; 16; 17; 18] stated that the most commonly used Nafion(r) dryer in the world was inadequate as a water pretreatment device for some compounds. It is very important to select a suitable water pretreatment device by the characteristics of the compound for accurate analysis and to protect the analytical instrument. In addition, because the amount of the analyte is usually very small, the degree of analyte loss by the water pretreatment device is very important. In order to solve this issue, a Desolvator-K called KPASS (Key compound PASSer)-Odor that could selectively remove water vapors in a different manner was investigated in this study. The manufactured Desolvator-K applied in this study is a water pretreatment device that inherited the principle of the Desolvator used by [PERSON] et al. [19], and it is an upgraded version of the Desolvator. The Desolvator-K in this study employed the Mpemba effect which was not depicted in the previous study [19] by removing water vapor with a temperature difference using Peltier.