The use of Carbotrap thermal desorption tubes for measurement of volatile and very volatile organic compounds

Status:

completed 12/2009

Aims:

The measurement of emissions from printer devices crucially includes the emission rates of volatile and very volatile organic compounds (VOCs and VVOCs), which at the same time are a key aspect in the tests performed for awarding of the "Blue Angel" environmental mark for these products.
The VOCs are sampled on an adsorbing agent in the form of Tenax® TA, a 2,6-diphenyl oxide-based porous polymer resin. The VOCs are subsequently thermally desorbed and analysed by means of gas chromatography (GC)/mass spectrometry (MS). For VVOCs, however, the suitability of this adsorbing agent is limited: the manufacturer states n-C7 to n-C26 for its range of use. The very volatile organic compounds such as ethanol, acetone and 2-propanol are not retained satisfactorily by Tenax® TA.
In the RAL-UZ 122 test procedure specified by RAL gGmbH for office equipment with a printing function, the use of Carbotrap is recommended for measurement of the VVOCs. Carbotrap sample carriers are of the type with multiple, different adsorption layers. According to the manufacturer's information, Carbotrap(TM) 300 should be used for the range from n-C3 to n-C30, and therefore for the measurement of both the VVOCs and the VOCs.
In order to improve the existing, unsatisfactory procedure, the use of Carbotrap(TM) 300 thermal desorption tubes for the measurement of VVOCs and VOCs was to be trialled.

Activities/Methods:

A solution of approximately 2 g of each substance was produced, consisting of acetone, dichloromethane, ethanol, methyl acetate and 1-propanol (VVOCs) and of n-hexane and toluene (VOCs). Direct application of the mixture to the sample carriers by means of a syringe proved impracticable, since the substance quantities introduced into the analysis system in this way led to overloading. For this reason, three different gas mixtures with concentrations of approximately 50 µg/m³, 100 µg/m³ and 300 µg/m³ of each substance were produced from the solution on the test gas facility at the BGIA - Institute for Occupational Safety and Health of the German Social Accident Insurance. From each of these test gases, three test samples were taken with Carbotrap 300 and Tenax® TA adsorption tubes under the usual conditions for the sampling of VOCs (sampling duration 30 minutes, volumetric flow rate 0.066 l/min). The Tenax® TA sample carriers were thermally desorbed on a PerkinElmer TurboMatrix ATD for 15 minutes each at 280 °C. The Carbotrap 300 tubes were thermally desorbed at 330 °C for 15 and 30 minutes. Following gas-chromatographic separation of the substances, they were analysed quantitatively by means of a flame ionization detector (FID). Qualitative analysis was also performed by mass spectrometry in order to identify any overlapping substances. The Carbotrap 300 sample carriers were thermally desorbed a second time under the same conditions as before, in order to ascertain whether the substances had been fully removed from the sample carriers during the first thermal desorption.

Results:

Thermal desorption of the Carbotrap 300 sample carriers for 15 minutes at 330 °C was sufficient for the substances employed. No components were detected during the second desorption. Higher contents were not determined at a longer desorption duration (30 minutes).
During the tests for recovery of the very volatile substances, i.e. acetone, dichloromethane, ethanol, methyl acetate and 1-propanol, clear differences were observed between Tenax® TA and Carbotrap 300. For ethanol and dichloromethane, higher values were noted with the use of Carbotrap, whereas 1-propanol and methyl acetate were adsorbed better on Tenax® TA. For acetone, a higher recovery was observed on Tenax® TA at the higher concentrations, whereas at the lowest concentration (50 µg/m³), the values were comparable to those of the Carbotrap 300 tubes.
The recovery values for n-hexane and toluene were approximately the same on the two materials.
Owing to these results, which indicate no improvement in the measurement of very volatile substances when Carbotrap 300 is used over the use of Tenax® TA sample carriers, no further steps were taken to define a measurement method for VVOCs. Should one of these compounds be detected during analysis of the VOCs on Tenax® TA, the analysis report clearly indicates that a lower result must be assumed for the substance concerned under the sampling conditions.

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