# Comparison of Water Pretreatment Devices for the Measurement of Polar Odorous Compounds
## 3 Results and Discussion
### Odorous Compound Recovery of Water Pretreatment Device  
#### 3.3.1 Recovery of Odorous Compounds  
In order to investigate the effect of water pretreatment devices on odorous compound analysis, experiments were conducted to compare the recovery of odorous compounds with respect to different devices. The recovery rates of the odorous compounds are illustrated in Figure 3.  
When water vapor was removed by Desolvator-K, the average recovery rates of MEK, i-BuAl, MIBK, BuAc and styrene were 103%, 96.6%, 99.5%, 97.9%, and 99.2%, respectively. For the Cooler-G, the average recovery rates of MEK, i-BuAl, MIBK, BuAc and styrene were 101%, 81%, 96.3%, 94.6%, and 90.9%, respectively. Likewise, average recovery rates of MEK, i-BuAl, MIBK, BuAc and styrene were 100%, 91.7%, 94.4%, 90.8%, and 88.6%, respectively, when the experiment was conducted with the Cooler-K.  
Figure 2: Water vapor removal of water pretreatment devices; (**a**) 50% RH; (**b**) 90% RH.  
The Desolvator-K revealed the highest recovery rates of all target compounds in all conditions even though MEK, i-BuAl, MIBK and BuAc have high solubility in water. This pattern was similar to a previous study. [PERSON] et al. [19] reported that recovery rates of sulfur compounds that also have high solubility in water were \(\geq\)97% for when the Desolvator was used to remove water vapor.  
In terms of i-BuAl, its recovery rate was lower than that of other compounds when the coolers were used. In contrast, although MEK has the highest solubility in water, its recovery rate was higher than that of i-BuAl. MEK dissolved rapidly in condensed water in the cooler, but it had a high vapor pressure (see Table 1), so it would be rapidly vaporized to maintain material equilibrium. However, i-BuAl dissolved quickly in the condensed water, but the time to equilibrium was delayed due to its low vapor pressure (see Table 1), and it would take time to revaporize. Thus, the i-BuAl recovery rate was low when the coolers were used.  
The recovery of the Cooler-G was higher than that of the Cooler-K for all compounds except i-BuAl due to the different impinger material between the Cooler-G and the Cooler-K. The impinger material of the Cooler-G was Teflon, and that of the Cooler-K was glass. [PERSON] et al. [28] investigated the absorption of gaseous compounds using various tube materials. It was reported that Teflon was not influenced by humidity or gas concentration compared to glass. Therefore, the Cooler-G with a Teflon impinger seemed to have higher recovery than the Cooler-K with a glass impinger.  
The U.S. EPA [4] reported that certain polar VOCs (amines, ketones, alcohols, and some ethers) were lost when water vapor was removed by a Nafion(r) dryer. Hence, the recovery of total non-methane organic compounds was reduced by 20-30%. Moreover, [PERSON] et al. [12] reported that all polar compounds were lost when a Nafion(r) dryer was used to remove water vapor. Some paraffins, olefins, and aromatic compounds were declined, and the total non-methane hydrocarbon concentration was reduced by 10-20%. In addition, [PERSON] et al. [29] noted that a large number of air pollutants are water soluble. Thus, a condensation dryer such as a cooler could remove analytes due to the interaction of condensed water and gas. [PERSON] [30] found that when water vapor was removed by using a cooler, O\({}_{3}\), which is a highly reactive compound, and SO\({}_{2}\), which is a water soluble compound, showed recoveries of 61.1-88.0% and 38.6-80.7%, respectively. According to these studies, when the Nafion(r) dryer and the cooler were used as water pretreatment devices for the analysis of polar materials, it was judged  
Figure 3: Recovery of each water pretreatment device: (**a**) Desolvator-K; (**b**) Cooler-G; (**c**) Cooler-K.  
that the analytical accuracy would be decreased. This suggests that the Desolvator-K should be an alternative way to remove water vapor for the analysis of polar compounds.