Quick Detection of Aldehydes and Ketones in Automotive Textiles


 This study was aimed to develop a quick detection method to test aldehydes and ketones in textiles in order to control the quality of automotive textiles in the development process from fabric production to end-use in vehicles. In this study, a pretreatment of samples was applied to simulate the actual environment of textiles used in vehicles. Collected volatiles were reacted with 2,4-dinitrophenylhydrazine and then eluted with acetonitrile tetrahydrofuran. The eluent was analyzed with high-performance liquid chromatography. Findings showed more than 90% volatiles could be detected in the established method; the lowest determination limit was 0.0297 mg/mL; and the lowest quantification limit was 0.0991 mg/mL, which meant sensitivity and capability of the method were high. Regression coefficients of linear models between volatile concentrations and chromatographic peak characteristics were >0.995, indicating that the method could effectively and efficiently determine the contents of volatiles in automotive textiles.


Introduction
In the market of automobiles, textiles have become important parts to provide suffi cient comfort and decoration, but volatile organic compounds (VOCs) that are often contained in automotive textiles have certain toxicity and could gradually evaporate to the air in vehicles. Aldehydes and ketones are the main VOCs in automotive textiles. These compounds are very harmful to human health and infl uence the sustainability of vehicles. Lots of testing standards are related to automotive VOC determination, but few research were carried out to detect volatile contents of textiles in vehicles. To improve the in-vehicle air quality, it is highly necessary to test VOC evaporated from automotive textiles in time [1,2]. Detection of VOC should be conducted in the entire production process of automotive textiles from fabric manufacturing to fi nishing to end products. Therefore, this study simulated the actual environment of textile using in vehicles and explored the highperformance liquid chromatography (HPLC) to determine the contents of aldehydes and ketones. The fi ndings of this research enable highly effective and effi cient determination of main toxic compounds volatilized from automotive textiles to control textile quality in the development process and to reduce air pollution in vehicles.

Testing standards of VOC
Current studies have shown that formaldehyde, benzaldehyde, and the other aldehydes and ketones are the main harmful volatile compounds in cars [3]. When some researchers analyzed VOC in vehicles, they found that the contents of formaldehyde and other aldehydes and ketones were higher than other compounds [4][5][6]. Thus, in this study, aldehydes and ketones are the main VOC detected in automotive textiles.
The literature reviews of testing standards present that the German Automobile Industry Association has proposed several testing standards for volatile substances in-vehicle parts. According to "Determination of Organic Emissions From Non-Metallic Materials in Vehicle Interiors" VDA 277-1995, volatile compounds under a static condition can be measured by the headspace method. "Thermo-Desorption Analysis of Organic Emissions for the Characterization of Non-Metallic Automobile Interior Materials" VDA 278-2002 specifi es that volatile and semi-volatile substances can be determined by thermal desorption analysis under dynamic conditions. Tests for the entire vehicle part need to be done in a sealed compartment. In addition, Japan and Russia have proclaimed related testing standards to test organic volatiles in cars [7]. In China, the State Environmental Protection Administration has declared "Evaluating Guidelines for Air Quality in Passenger Vehicles" GB/T 27630-2011, which limits the contents of formaldehyde, acetaldehyde, and acrolein separately less than 0.10, 0.05, and 0.5 mg/m 3 in vehicles [8].
Current testing standards of VOC focus on quantitative analysis of each compound in the car, rather than on general qualitative analysis. In addition, in the current testing methods, the air quality is measured in whole vehicles, and it is very diffi cult to supervise volatile substances in different vehicle parts before

Abstract:
This study was aimed to develop a quick detection method to test aldehydes and ketones in textiles in order to control the quality of automotive textiles in the development process from fabric production to end-use in vehicles. In this study, a pretreatment of samples was applied to simulate the actual environment of textiles used in vehicles. Collected volatiles were reacted with 2,4-dinitrophenylhydrazine and then eluted with acetonitrile tetrahydrofuran. The eluent was analyzed with high-performance liquid chromatography. Findings showed more than 90% volatiles could be detected in the established method; the lowest determination limit was 0.0297 mg/mL; and the lowest quantifi cation limit was 0.0991 mg/mL, which meant sensitivity and capability of the method were high. Regression coeffi cients of linear models between volatile concentrations and chromatographic peak characteristics were >0.995, indicating that the method could effectively and effi ciently determine the contents of volatiles in automotive textiles.

Keywords:
Volatile organic compounds, automotive textiles, high-performance liquid chromatography, aldehydes, ketones assembling, so that contents of VOC released from each part cannot be detected in time. To provide good air quality in vehicles, each in-vehicle part or interior materials including automotive textiles should be detected and meet standard requirements. Generally, there is a lack of specialized testing standards for detecting VOC in automotive textiles, so this study was aimed to establish an effective and reliable testing method to detect mainly aldehydes and ketones in automotive textiles before the car assembling.

Testing methods of aldehydes and ketones
Methods for volatile substances collection and analysis include detection module, headspace method, thermal analysis method, and sampling bag method [9,10]. The detection module method is commonly used to test VOC in the whole vehicle, and it is not suitable for interior textiles. The cost and testing conditions of this method are very high, and it is often applied by motor corporations or third-party testing organizations. The headspace method is easy to implement and the cost is relatively low. In this method, the entire quantity of organic volatile substances in vehicles is tested, but each substance cannot be analyzed. The thermal analysis method is only used to detect benzene and hydrocarbons. The sampling bag is the most common method used in Japanese car corporations. Tested samples are put into a sealed bag. This method is very convenient to operate and is friendly to small sample sizes. In comparison, the sampling bag is the most feasible method to collect aldehydes and ketones in automotive textiles.
Detection methods of aldehydes and ketones include gas chromatography and liquid chromatography [11][12][13]. When the contents of aldehydes and ketones in the air are less, the sensitivity and accuracy of instruments need to be high enough. In addition, compounds such as formaldehyde and acetone do not have UV-responsible groups to be detected in the UV detection method. Aldehydes and ketones could react with 2,4-dinitrophenylhydrazine (DNPH) in a strong acid condition, and the derivatives have high sensitivity in liquid chromatography [14]. According to "Determination of Formaldehyde in Ambient Air Using Adsorbent Cartridge Followed by High Performance Liquid Chromatography (HPLC)" EPA-TO-11, liquid chromatography is commonly used to detect aldehydes and ketones organic volatiles in the air. Therefore, this study selected HPLC to test aldehydes and ketones in automotive textiles.

Simulation of the inner environment in vehicles
The inner environment of vehicles is relatively complex. When windows and doors were closed for a certain time, in addition to aldehydes and ketones, lots of nitrogen exit inside the vehicle, and harmful volatile matters are hard to spread out [15]. Referring to standards "Interior Air of Road Vehicles-Part 2: Screening Method for the Determination of the Emissions of Volatile Organic Compounds from Vehicle Interior Parts and Materials-Bag Method" CNS15676-2-2013 and "Determination of Volatile Organic Compounds and Carbonyl Compounds in Cabin of Vehicles" HJ/T400-2007, the study designed sealed bags with insert materials such as polyvinylidene fluoride to isolate outside air and to avoid reaction with organic compounds in bags. Then the sealed bags were filled with pure and dry nitrogen to simulate the enclosed inner environment of vehicles.
When the vehicle is exposed to the sun for a long time, the inner temperature increases rapidly which can accelerate the volatilization of aldehydes and ketones in a short time [16]. In this study, treated samples were placed in an oven to simulate the condition of the sun exposure. Two aldehyde reagents and two ketone reagents were used to simulate VOC evaporated from automotive textiles.
After cooling the bags, adsorption tubes fi lled with DNPH were used to adsorb aldehyde and ketone volatiles in bags. Organic volatiles can react with DNPH to form a stable hydrazine derivative in acidic conditions. Then adsorption tubes were eluted with acetonitrile tetrahydrofuran. The collected 5 mL eluent was analyzed by the HPLC method to determine the contents of each aldehyde and ketone volatiles. The testing conditions of HPLC are shown in Table 1.

Material and solutions
In this study, to validate the effi ciency and effectiveness of the pretreatment and the HPLC method, linear regression models of concentrations and chromatographic peaks were developed. Four aldehyde/ketone-DNPH solutions including formaldehyde, hexanal, butanone, and cyclohexanone were applied to investigate the effects of concentrations on liquid chromatography. Nine concentration levels of each standard aldehyde/ketone-DNPH solution were 15μ, 7.5μ, 3.75μ, 1.875μ, 0.9375μ, 0.4688μ, 0.2344μ, 0.0586μ, and 0.0293 μg/ mL, respectively. With the lowest concentration (0.0293 μg/mL), 10 samples were treated with each mixed solution, yielding 40 samples. According to the results of liquid chromatography, limit of detection (LOD) and limit of quantitation (LOQ) in the HPLC method were identifi ed.
Fabric samples were woven with polyester, and their size was 10 cm × 10 cm. Four types of aldehyde and ketone solutions added to woven fabrics were formaldehyde, hexanal, butanone, and cyclohexanone. Of note, 0.05 g pure solutions were mixed with acetonitrile solutions in 50 mL volumetric fl ask and made into 1000 μg/mL with standard aldehyde and ketone solutions. For each monomer solution, 100 μL was added to fabric samples for pretreatment and detected contents in HPLC were compared with the added amount.

Results and discussions
Clear chromatograms in Figure 1 indicated that each VOC could be separated in the method of liquid chromatography with the designed parameter setting. The retention time of formaldehyde, hexanal, butanone, and cyclohexanone could be obtained and is shown in Table 2.

Linear analysis
To estimate the effi ciency of HPLC in determining volatiles of automotive textiles, linear analysis had been done to compare characteristic peak in chromatogram with the concentration of volatiles. High correlation means the method could effectively and effi ciently determine the contents of the volatiles [17].
In this study, LOD and LOQ of formaldehyde, butanone, cyclohexanone, and hexanal were obtained. According to the results in Table 4, LOD and LOQ are relatively low, which means the pretreatment method and HPLC method could detect VOC even with low concentration.

Accuracy and precision of the method
Differences between the added quantity of aldehyde and ketone volatiles and the detected contents of those volatiles in HPLC could validate the accuracy of the method to determine VOC in automotive textiles. Lower differences prove less loss of VOC Linear models for formaldehyde, hexanal, butanone, and cyclohexanone are separately illustrated in Figures 2-5.
Regression coeffi cients of each model are listed in Table  3, and they are >0.995, indicating that four standard curves have very high linear correlations. Therefore, the peak area in chromatogram could be used to represent the contents of aldehyde and ketone compounds in tested samples, and the method provides an effi cient and effective way of determining VOC of automotive textiles.
Findings in this study provide a useful method to test aldehyde and ketone volatiles in automotive textiles, as well as other in-vehicle products. In comparison with current VOC testing methods, this new detection method is more appropriate to test aldehyde and ketone volatiles in interior materials. This simple and quick method can be used in the entire development process of automotive textiles to detect harmful volatiles in time in order to avoid VOC of textiles after vehicle assembling. The results of the research will provide a theoretical foundation for establishing testing standards of VOC in automotive textiles and benefi t promoting sustainable production of automotive textiles and reducing VOC in the whole vehicles. Due to limited time and resources, this study explored only four typical aldehyde and ketone compounds, and other volatiles were not discussed in this paper but could be investigated in future research.
Funding: This research was funded by the National Natural Science Foundation of China, grant number 71704021.
in the process of testing and declare that the results in HPLC can accurately present the contents of VOC in textiles. Usually, the ratio of detected contents and added quantity should be above 50% [20]. Precision was proved by the relative standard error (RSD) as shown in the following equation: where n equals sample repeats; i X represents detected content of volatiles in each sample; and X represents average of detected contents.
In the experiment, 100 μL standard formaldehyde, hexanal, butanone, and cyclohexanone solutions were, respectively, added to blank woven fabrics. For each treatment, six samples were pretreated and detected contents of each volatile were collected.
In Table 5, differences between the added amount and detected contents are very low. Of note, 94.48% formaldehyde, 93.23% hexanal, 98.61% butanone, and 91.12% cyclohexanone could be detected. Findings reveal that HPLC is an easy and repeatable method that can accurately and precisely determine the contents of VOC in automotive textiles.

Conclusions
Textiles are important parts of vehicles as interior decoration. Many chemical additives have to be added in automotive textiles to improve durability and colorfastness and to enhance