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Note 63: Determination of Volatile and Semi-Volatile Organics in Printer Toners Using Thermal Desorption GC Techniques

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By John J. Manura and Eric Butrym
1999

INTRODUCTION

The quality of indoor air has become a major concern to the entire population. Numerous findings have been previously reported describing the "sick building syndrome" which has been associated with the quality of indoor air in public buildings. Health risks due to these "sick buildings" have caused concern in government and industry due to both time lost by sick employees and the costs involved with remediation. Building related health problems may be due to contamination of indoor air by emissions of volatile organic compounds (VOC's) from a variety of sources including construction materials, fabrics, furnishings, maintenance supplies, adhesives, paints, caulks, paper, cleaning products and office equipment. In particular, the toners used in copy machines and computer printers contain a large number of volatile and semi-volatile organics that have the potential to contribute to indoor air contamination in a closed office environment. Because many of the volatile emissions and by-products from these products are toxic, additional knowledge of the levels of these organic chemicals in the indoor air environment is required in order to determine human health impact. New methods are needed to accurately determine the identity and the levels of these volatile organics in indoor air samples. Additional studies will be needed to determine the sources of the air contamination.

In this paper, the direct thermal extraction technique is used to determine the volatile components in a number of PC printer and copy toners widely used in an office environment. In this technique, the analytes from solid matrix toner samples are thermally extracted directly into the GC injection port. The method requires no sample preparation and mimics the conditions the toner experiences in the printer or copier system. This is a fast, low cost method of analysis that can be readily developed into a quality control analysis method. Both new and used toners are compared to determine the volatiles that are removed from the toners during normal use and emitted into the office environmental air.

Instrumentation

All experiments were conducted using a Scientific Instrument Services model TD3 Short Path Thermal Desorption System accessory connected to the injection port of an HP 5890 Series II GC interfaced to an HP 5989A Mass Spectrometer. The mass spectrometer was operated in the electron impact mode (EI) at 70 Ev and scanned from 50 to 550 daltons during the GC run for the total ion chromatogram. All peaks in the resulting GC chromatogram were searched and identified using the HP ChemSation software and the Wiley NBS library.

A 60 meter, 0.25 mm I.D. x 0.25u film thickness J&W DB35MS capillary column was used for the analysis at a column flow rate of 1.0 milliliter per minute. The GC injection port was set to 260 degrees C and a direct splitless analysis was used. The head of the column was maintained at -68 degrees C using a SIS Micro Cryo-Trap (Scientific Instrument Services, Ringoes, NJ) during the desorption and extraction process. The Cryo Trap was ballistically heated to 250 degrees C after the desorption process was complete and then the GC oven was temperature programmed from 30 degree C (hold for 5 minutes) to 300 degrees C at 5 degrees /min.

The "Direct Thermal Extraction Technique" was used in conjunction with the SIS Short Path Thermal Desorption system. This technique utilizes a thermal desorption apparatus attached to the injection port of a GC/MS system and permits the direct thermal extraction of volatile and semi-volatile organics directly from small sample sizes (1 to 100 mg) without the need for solvent extraction or other sample preparation (Figure # 1).

Figure 1

Figure 1 - SIS Short path Thermal Desorption System

Experimental

A variety of toners from copy machines and computer laser printers were collected for analysis. Both new (unused) as well as depleted (used) toners were collected. For the analysis, 10 milligrams of the toner was placed into a preconditioned blank desorption tube on top of a glass wool plug. The desorption tube containing the sample was attached to the Short Path Thermal Desorption System and a syringe needle attached. The desorption tube with sample was injected into the GC injection port, the heating blocks were closed around the sample and the desorption tube was ballistically heated to the stated desorption temperature. The carrier gas flow through the sample purged the volatiles from the heated toner sample into the injection port and onto the front of the GC column were they were cryo-focused at -68 degrees C in a narrow band at the front of the GC column (Figure # 1). After the 5 minute desorption process was complete, the cryo trap was rapidly heated to 250 degrees C to release the volatiles for subsequent GC analysis. The GC was temperature programmed at the conditions above and the resulting peaks in the chromatogram identified using the mass spectrometer and mass spec library.

Four different unused printer and copier toners were analysed. Each of these toners was first analyzed at different desorption temperatures in order to determine the optimum conditions for the thermal desorption process. The toners were analyzed at thermal desorption temperatures of 100, 150, 200 and 250 degrees C. Each of these toners was also compared to one another to determine the variances in toners from different machines from different manufacturers. Finally, depleted or used toners from these same printers were analyzed and compared to the new or unused toners. The compounds, which were not present in the used toners, account for the volatiles that are released into the office environment during use of these printers and copiers.

Results and Discussion

Figure 2

Figure 2 - Copy Toner XN-1

In Figure # 2, a new copy machine toner (Sample Number XN-1) was desorbed at various temperatures in order to determine the optimum desorption temperature for analysis of all samples. A second new laser printer toner (Sample Number SN-1) was analyzed in the same manner as shown in Figure # 3. As anticipated, the higher the desorption temperature, the higher the range of volatiles and semi-volatiles purged from the toner sample. At a desorption temperature of 100 degrees C, the major peaks in the chromatograms of both samples were Toluene, Xylenes, Styrene, and a few low molecular weight aldehydes and alkanes. At higher temperatures, a larger range of aromatics, alkanes, aldehydes, and acidic compounds were detected. The sensitivity of the technique nearly doubled at a desorption temperature of 200 degrees for many of the anlaytes present as compared to the lower temperatures. Based on the analysis of these two samples plus the analysis of two additional printer toners, a desorption temperature of 200 degrees C was selected as the optimum temperature at which to analyze all subsequent samples. This temperature produced a wide range of volatiles and semi-volatiles with minimal decomposition of the samples.

Figure 3

Figure 3 - Printer Toner SN-1

Figure 4

Figure 4 - Comparison of Differect Printer and Copy Toners

In Figure #4, four different new printer and copier toners were analyzed via the thermal desorption technique to compare toners for different instruments and manufacturers. Sample XN-1 was a copy machine toner, sample SN-1 was a laser printer toner, and samples HN-1 and HN-2 were two toner samples from the same manufacturer but for two different models of their laser printers. As can be seen from the total ion chromatograms, there is significant variation between the various manufacturers and models of printer and copy machine toners. Even the two toners from the same manufacturer but for different models of laser printers (HN-1 and HN-2) exhibited significant differences in the analytes present. Major concentrations of toluene, styrene and the xylenes were common to most of the toners. Other prevalent analytes in some of the samples included acetophenone, benzaldehyde, butanol, methyl styrene, phenol, benzoic acid and a large number of substituted benzenes.

Figure 5

Figure 5

Figure 6

Figure 6

Figure 7

Figure 7

In Figures #5, #6, and #7, the three different new laser printer toners were compared to depleted or used toners from the same printer. In the operation of the laser printers and copiers, the toner is exposed to a heated drum or surface which volatilizes the low boiling compounds thereby removing these low boiling volatiles from the toner. As expected, in all three used toner samples, the low volatiles are either missing or present in deduced concentrations and only the higher molecular weight volatiles and semi-volatiles were present in their original concentration. In particular, the toluene, styrene, and the xylenes were not present in the depleted toners. Apparently these chemicals were removed from the toner and emitted into the office air during the normal operation of these printers.

Conclusion

Many products which are used in the office workplace, including copy machines and computer laser printers, are responsible for contributing to the levels of volatiles in the indoor air environment. These copiers and laser printers use toners which can emit a number of chemicals into the office environment. These chemicals include toluene, styrene, the xylenes, low molecular weight alkanes and aldehydes. Other materials in the office including office furniture, building materials, flooring materials and other office equipment can also contribute to the levels of chemicals emitted into the office environment. Individually, the contribution from any one product may not be significant. However, the cumulative levels of emissions from these products are increasingly becoming a concern. This is particularly noteworthy in the new energy efficient construction of buildings. These buildings minimize air exchange due to the tight construction and recylcing of interior air. In the future, the levels and extent of the volatile organics in indoor air will come under closer scrutiny by both the public and scientific communities. The technique of "Direct Thermal Extraction" and the subsequent analysis using the Short Path Thermal Desorption System in conjunction with a gas chromatograph and mass spectrometer has proven to be a useful technique for the analysis of office products including printer toners, paper, plastics, carpeting and office finishes which are the sources of indoor air contamination. This will continue to be a useful and efficient technique for the analysis of office and building materials for the determination of volatile emissions from these products.