Note 22: Comparison Of Volatile Compounds In Latex Paints

INTRODUCTION

The identification and quantification of volatile organic compounds (VOC's) in latex paints are extremely important to paint manufacturers. Potential health risks exist due to the toxic nature of many of these components. In addition, building related problems may be caused by the contamination of indoor air by emissions of VOC's from paints that have been used. The paint industry shares a common concern by now manufacturing latex paints without the use of solvents to reduce the amount of VOC's in paints to help eliminate potential health risks. Analytical techniques are needed to identify and quantitate VOC's present in latex paints, so these techniques can be incorporated into troubleshooting problems that may arise as well as be used in a quality control program. Volatile organic compounds were collected from several commercial latex paints including paints manufactured without the use of solvents by using a purge and trap technique (P&T), followed by trapping on an adsorbent resin and subsequent analysis by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). The volatile organics present in the latex paints were quantified using matrix spiked deuterated standards. A method was also developed to quantify total VOC's as well as individual hydrocarbons, aromatics and halogens. This technique can be easily incorporated into a troubleshooting technique to detect problems in various commercial latex paints, to compare competing manufacturers products, as well as implementation into a quality control program.

Figure 1 - Purge & Trap Apparatus

Instrumentation

Samples were collected using a Scientific Instrument Services Purge & Trap System. This apparatus (Figure 1) consists of a sparge gas inlet connected to a stainless steel purging needle that is inserted through an adaptor fitting into a 10 ml test tube. A dry purge gas inlet is located at a right angle to the sparge gas inlet at the top of the apparatus. This can be left in the closed or open position. The purpose of the dry purge is to reduce the water vapor condensation on the adsorbent trap. This problem can be especially troublesome when isolating volatiles from aqueous solutions at high temperatures. Although the adsorbent traps packed with Tenax® have a low affinity for water, it is inevitable that some condensation will occur in the trap due to the high relative humidity of the sparge gas as it exits the apparatus. When moisture condenses on the adsorbent, it can block the pores of the resin matrix and thereby drastically reduce the diffusion of volatile organics into the trapping agents. This will result in reduced trapping efficiency. Opposite the dry purge inlet is the connector for the glass-lined stainless steel (GLT) desorption tube containing the adsorbent resin. The liquid purging system also contains two ball rotameters with adjustable needle valves mounted on a stationary base and permits the visual indication and independent adjustment of the carrier gas flow to each of the gas inlets.

All experiments were conducted using a Scientific Instrument Services model TD-2 Short Path Thermal Desorption System accessory as described elsewhere (1&2) 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 400 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 30 meter x 0.25 mm i.d. DB-5MS capillary column containing a 0.25 um film thickness. The GC injection port was set to 250 degrees C and a 20:1 split was used. The head of the column was maintained at -70 degrees C using an S.I.S. Cryo-Trap model 951 during the desorption and extraction process and then ballistically heated to 200 degrees C after which the oven was temperature programmed from 35 degrees C (hold for 5 minutes) to 80 degrees C at a rate of 10 degrees /min and to 280 degrees C at 4 degrees /min.

Experimental

Eight latex paints (gloss, semi-gloss, 2 flats, vinyl acrylic, enamel, satin, and a non-solvent latex) were analyzed to compare and quantify the volatile organics of different manufacturers brands. For quantification, an internal standard was spiked into the adsorbent traps after the sample had been isolated. No correction for extraction efficiency of recovery is achieved using this technique; however, it serves as a useful means of quantifying the levels of components present on the adsorbent traps.

Sample sizes of 0.2 ml of commercial paint diluted in 5 ml of distilled water (25:1) were pipetted into a 10 ml test tube and heated to 60 degrees C. Samples were sparged with high purity helium at 20 ml/min with an additional 25 ml/min dry purge for 20 minutes using an S.I.S. Purge & Trap System. Volatile analytes were gas extracted and carried to a preconditioned 4.0 mm i.d. glass-lined stainless steel desorption tube packed with 100 mg of Tenax TA. Once the samples were collected, they were spiked with 300 ng of a d-8 toluene internal standard by injecting 3 ml of a 100 ng/ml of a d-8 toluene stock solution in methanol by syringe injection into the Tenax matrix. The desorption tubes with sample and internal standard were then attached to the Short Path Thermal Desorption system and a syringe needle attached. The desorption tube was injected into the GC injection port at desorption block temperatures of 220 degrees C for 5 minutes.

Results and Discussion

Eight commercial latex paints were analyzed to identify, compare and quantify the total volatile organics present as well as individual hydrocarbons, aromatics and halogens. Each chromatogram contains an insert showing the relative amounts of hydrocarbons, aromatics and halogens in each paint. The paints were found to contain numerous straight and branched chain hydrocarbons and alcohols in addition to many benzene derivatives. Trace amounts of the aromatic compounds benzene, toluene and xylene were also present. High concentrations of the compounds 1,1'-{methylenebis (oxy)}-propane and 2-(2-butoxyethoxy)-ethanol in addition to the halogenated compound chlorobenzene were identified in the glossy latex paint (Figure 2). The semi-gloss latex contained over 100 volatile organic compounds (Figure 3), many of which were substituted benzenes. Butyl esters of propanoic and butanoic acids were also detected in the semi-gloss latex (Figure 3). Although each flat latex had its own fingerprint chromatograph, they possessed many common compounds such as ethylbenzene; 1,3-dimethyl benzene; butyl esters of propanoic acid and the aromatic compound toluene as well as straight and branched chain hydrocarbons (Figures 4a & b). Numerous monoterpenoid compounds such as delta-3-carene, isocineole, limonene, 1,8-cineole, alpha & gamma terpinene, alpha terpinolene and 1,4-terpineol were identified in the vinyl acrylic latex (Figure 5). The Merck Index lists these compounds as constituents of several plant derived essential oils which are used as fragrance materials. The latex enamel was found to contain a high concentration of the aromatic compound toluene in addition to numerous straight and branched chain hydrocarbons (Figure 6). The satin latex which exhibited a volatile organics profile similar to that of the flat latex also contained the compounds 1,1,1-trichloroethane, 2-methyl-2-nitro-propane and 1,1'-oxybis-butane (Figure 7). Butyl esters of propanoic acid and propyl esters of butanoic and propanoic acids were routinely identified in the non-solvent latex (Figure 8). However, the compounds 2-methyl-,2,2-dim propanoic acid and 2-ethyl-3-hydroxyhexyl ester which were detected in high concentrations in the other latex paints were not found in the non-solvent latex (Figure 8).

Figure 2 - Glossy Latex Paint

Figure 3 - Semi-Gloss Latex Paint

Figure 4a - Flat Latex Paint

Figure 4b - Flat Latex Paint

Figure 5 - Vinyl Acrylic Paint

Figure 6 - Latex Enamel Paint

Figure 7 - Satin Latex Paint

Figure 8 - Non-solvent Latex Paint

Conclusion

The Short Path Thermal Desorption System used in conjunction with the Purge & Trap System permits the identification and quantification of trace levels of volatile organics in latex paints. These techniques present a tremendous improvement over the time consuming solvent extraction techniques normally used in the laboratory. New methods which reduce or eliminate the solvents required for sample purification provides many advantages to the laboratory. The exposure of laboratory personnel to these solvents has become of major concern to both employees and health officials. The disposal of used solvents has become a serious problem and is rapidly becoming quite expensive. The Short Path Thermal Desorption System permits the analysis of samples without any prior solvent extraction. The paint industry also shares a common concern by now manufacturing latex paints without the use of solvents to reduce the amount of VOC's in paints to help eliminate potential health risks. This technique has also been applied to other applications such as quantification of benzene and toluene in food products (3), and flavors and fragrances in food products (4&5), commercial products (6) and plant material (7). This technique can be easily incorporated into a troubleshooting technique to detect problems in various commercial colognes, to compare competing manufacturers products, as well as implementation into a quality control program.

References

1. Manura, J.J., S.V. Overton, C.W. Baker and J.N. Manos. 1990. Short Path Thermal Desorption - Design and Theory. The Mass Spec Spurce Vol. XIII (4): 22-28.

2. Manura, J.J. and T.G. Hartman. 1992. Applications of a Short Path Thermal Desorption GC Accessory. Am. Lab. May: 46-52.

3. Methodologies for the Quantification of Purge and Trap Thermal Desorption and Direct Thermal Desorption Analyses. S.I.S. Application Note No. 9, September 1991.

4. Patt, J. M., Rhoades, D.F. and J.A. Corkill. 1988. Analysis of the Floral Fragrance of Platanthera stricta. Phytochemistry. Vol. 27: 91-95.

5. Manura, J.J. 1993. Quantitation of BHT in Food and Food Packaging by Short Path Thermal Desorption. LCGC Vol. II (2): 140-146.

6. Hartman, T.G., Karmas, K., Chen, J., Shevade, A., Deagro, N., and H. Hwang. 1992. Determination of Vanillin, Other Phenolic Compounds, and Flavors in Vanilla Beans. ACS Symposium Series 506. Phenolic Compounds in Food and Their Effects on Health. I. Chi-Tang Ho, Chang Y. Lee, and Mon-Tuan Huang, Editiors. pp. 60-76.

7. Patt, J.M., T.G. Hartman, R.W. Creekmore, J.J. Elliot, C. Schal, J. Lech, and R.T. Rosen. 1992. The Floral Odour or Peltandra Virginica Contains Novel Trimethyl-2,5-Dioxabicyclo [3.2.1] Nonanes. Phytochemistry. Vol 31 (2): 487-491.