Note 36: Identification Of Volatile Organic Compounds In a New Automobile

INTRODUCTION

The quality of indoor air has become a major concern to the entire population. In addition to industry and other businesses, the identification and quantification of volatile organic compounds (VOC's) in newly manufactured automobiles are extremely important to the automobile industry. The contamination of indoor air is caused by emissions of volatile organic compounds (VOC's) from a variety of sources including fabrics, upholstery, carpets, adhesives, paints, cleaning materials as well as from exhaust fumes outside the vehicle. Potential health risks exist due to the toxic nature of many of these components. Individually, the contribution from any one product may not be significant, but the cumulative levels of emissions from these products are increasingly becoming a major concern. Because many of the volatile emissions and by-products from these products are toxic, additional knowledge of the levels of these organic compounds in the car's interior is required in order to determine human health impacts. Analytical techniques are needed to identify and quantitate VOC's present in these areas to help identify potential health risks. Further studies will also be required to determine the sources of the air contamination. If manufacturing processes are contributing to poor air quality, then the manufacturing processes will need to be improved to limit the emission of VOC's. For this study, air samples were collected over a period of time from a new automobile to determine the presence and changes of VOC's over time. Samples were collected by pumping 10.0 liters of air through a desorption sampling tube and trapping the volatiles on an adsorbent resin inside this sample tube. The volatile organics present in the automobile's interior were quantified using matrix spiked deuterated standards. The samples were then analyzed by thermally desorbing the trapped volatiles into a gas chromatograph using a thermal desorption system and subsequently analyzing the eluted organics via gas chromatography-mass spectrometry (GC-MS).

Instrumentation

All experiments were conducted using a Scientific Instrument Services model TD-3 Short Path Thermal Desorption System accessory connected to the injection port of an HP 5890 Series II GC interfaced to an HP 5971 Mass Selective Detector. The mass spectrometer was operated in the electron impact mode (EI) at 70eV and scanned from 35 to 550 daltons during the GC run for the total ion chromatogram. A short 0.5 meter by 0.53 mm diameter fused silica precolumn was attached to the injection port end of a 60 meter x 0.25 mm i.d. DB-5MS capillary column containing a 0.25 um film thickness. This precolumn acts as a cold trapping area for the desorbed materials and also protects the capillary column and extends its lifetime. The GC injection port was set to 260 degrees C and a direct splitless injection was used. The head of the column was maintained at -70 degrees C using an S.I.S. Cryotrap model 951 during the desorption and extraction process and then ballistically heated to 200 degrees C after which the GC oven was temperature programmed from 35 degrees C (hold for 5 minutes) to 80 degrees C at a rate of 10 degrees C/min, then to 200 degrees C at 4 degrees C/min, and finally to 260 degrees C at a rate of 10 degrees C/min.

Experimental

Six air samples collected both in the Summer and Fall of 1995 from a 1995 Lincoln Continental were analyzed to identify and compare the volatile organics present over a two month period. All samples were collected using a Gilian model LSF-113 low flow air sampling pump (Fig. 1). This unit maintains a constant flow over variable back pressure within +/-5% of the set point. All samples were collected for 100 minutes at 100 ml/min (10 L total) through preconditioned 4.0 mm i.d. glass-lined stainless steel desorption tubes packed with 200 mg of Tenax® TA. Once the samples were collected, they were purged with helium at 50 ml/min for 8 minutes and then spiked with 100 ng of d-14 cymene internal standard by injecting 1 ul of a 100 ng/l of a d-14 cymene stock solution in methanol by syringe injection into the Tenax matrix.

The desorption tube with sample and internal standard was then attached to the Short Path Thermal Desorption System and a syringe needle attached. The desorption tube was injected into the GC injection port and desorbed at a desorption block temperature of 250 degrees C for 10 minutes. The desorbed volatiles were trapped at the front of the GC column and subsequently eluted through the GC column for detection and identification by the mass spectrometer.

Results and Discussion

Three air samples taken from a 1995 Lincoln Continental on July 19, 1995 with an additional three air samples collected on September 19, 1995 were analyzed to determine the presence and changes of VOC's over time. Samples were collected from the airtight vehicle at 9:55 am, 12:00 noon and 1:20 pm on July 19 at temperatures of 115.1 degrees F, 123.8 degrees F and 122.2 degrees F, respectively. On September 19, samples were collected at 10:25 am, 12:05 pm and 1:47 pm at temperatures of 109.2 degrees F, 121.0 degrees F and 100.5 degrees F, respectively.

Over 100 volatile organics were identified in the air samples analyzed. The air samples studied produced 50 or more volatile organics which were identified in addition to many more that were either too weak to identify or in which a good NBS library match was not achievable. The air sample collected at 9:55 am on July 19 (Fig. 2) was found to contain the aromatic compound toluene as well as numerous straight and branched chain hydrocarbons which may have outgassed from the automobile's interior and also are the common by-products of gasoline and its associated exhaust fumes. The siloxanes hexamethyl-cyclotrisiloxane, octamethyl-cyclotetrasiloxane and decamethyl-cyclopentasiloxane were also detected and are related to cleaning and lubricating compounds. As the temperature increased in the automobile from 115.1 degrees F to 122.2 degrees F (Figs. 3&4) during the day, the concentrations of these compounds also increased together with the appearance of styrene (Fig. 4), numerous substituted benzenes and the anti-oxidant compound BHT. These benzene derivatives are common in gasoline, paints and carpeting whereas BHT is common in treatments (such as "Armour All") for leather and vinyl. Styrene, a residue of styrene-butadiene-rubber (SBR) latex glue, is used in the manufacturing of carpets. Phenol, a general disinfectant and 1-methyl-2-pyrrolidinone which is used as an industrial solvent for polymers and in petrolium processing were detected during the second collection period which was the hottest period of the day at 123.8F (Fig 3).

After two months, the concentrations of VOC's in the Lincoln Continental were significantly decreased (Figs. 5-7). Styrene, phenol, 1-methyl-2-pyrrolidinone and the anti-oxidant BHT were not detected and the number of benzene derivatives were greatly reduced. However, the aromatic compound benzene and numerous flavor and fragrance compounds such as hexanal, octanal, nonanal and other aldehyde derivatives were identified. In addition, trace amounts of trichloroethane possibly derived from paint were detected (Fig. 7). As the temperature increased in the vehicle from 109.2F to 121.0F at 12:05 pm (Figs. 5&6), the concentrations of the volatile organics also increased. Although, when the temperature decreased to 100.5F later in the day, the concentrations of these compounds were subsequently reduced (Fig. 7). This suggests that the emission of VOC's decreased in a new automobile over time but remained temperature dependent.

Conclusion

The Short Path Thermal Desorption System used in conjunction with a high quality air sampling pump permits the identification and quantification of a broad range of volatile organics in an enclosed area. This technique permits quick analysis of samples without the need for difficult, time consuming and environmentally unfriendly solvent extractions. Although the concentrations of VOC's were significantly reduced over time in a new automobile, the exposure of the public to such compounds that were identified should be of concern to both the automobile industry and health officials. These air samples show that the public is constantly in contact with a wide variety of potentially harmful VOC's due to cleaning supplies, lubricants and fuel by-products. Because of the potential toxic nature of many of these compounds, additional knowledge of the levels of these organic compounds in the car's interior is required in order to determine human health impacts.