A PASSIVE TUBE-TYPE SAMPLER FOR THE DETERMINATION OF FORMALDEHYDE VAPOURS IN MUSEUM ENCLOSURES
| Main Authors: | , |
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| Format: | Article |
| Language: | English Slovak |
| Online Access: | http://www.viks.sk/chk/studcon_4_01_289_303.doc |
| Abstract: | SUMARRIES. A tube-type passive sampling method has been developed and assessed for the quantification of formaldehyde (methanal) vapours in indoor air. The sampler was designed for use in museums where test sites often include small enclosures with low air movement. The procedure involves collection of formaldehyde vapours in a Palmes diffusion tube containing a paper support impregnated with an acidified solution of 2,4-dinitrophenylhydrazine (2,4-DNPH). After sampling, quantification of the trapped F-DNPH is achieved by high performance liquid chromatography (HPLC) analysis with UV detection at 350nm. To validate the procedure, permeation devices were used to generate formaldehyde-containing atmospheres, 81-2975ppb, in a 20dm3 chamber so that experimentally derived sampling rates could be calculated and compared with the theoretical value. Three 2,4-DNPH solutions were investigated to obtain an efficient and stable trapping solution. Best results were achieved with a 27mg.ml-1 solution of 2,4-DNPH which contained 4-5%v/v orthophosphoric acid. At 55% RH, and with low airflow in the chamber, the experimentally derived sampling rate of 1-34 +- 0-17ml.min-1was in good agreement with the theoretically derived sampling rate of l-36ml.min-1. The passive sampling method was repeatable and reproducible with RSD (relative standard deviation) values below 7% for long-term exposures at low air velocities. CONCLUSION. Samplers prepared with a high acid concentration (solution A) demonstrate the need to control the amount of acid added to the trapping reagent used in this study. Samplers prepared with approximately 5% acid trapping solution (solutions B and C) performed well over the formaldehyde concentration range used in this study. The amount of 2,4-DNPH used in the trapping solution does not have to be rigorously controlled as long as the number of moles of reagent used is far in excess of the number of moles of formaldehyde it will react with (see comparison of solutions B and C). In addition, the presence of a wetting agent did not appear to affect the performance of the sampler; however, blank tubes prepared with the solution without the wetting agent did give slightly lower blank values with better reproducibility. Mean experimentally derived sampling rates at 55% RH and with low airflow in the chamber differed from the theoretical sampling rate by 1 and 5% for trapping solutions B and C, respectively. When the humidity was decreased to 5%, the mean experimentally derived sampling rates of the sampler differed from the expected value by 9 and 5% for solutions B and C, respectively. Since this humidity was extremely low and the sampling rate was little affected, it is thought that small fluctuations in humidity experienced in the museum environment would not affect the sampling rate of the tube sampler. Repeatability of the sampler has shown that, within individual experiments, typical RSD values were below 7%. Samplers were stable, even at room temperature, for up to 35 days. It is advisable to deploy the device in the museum environment for a minimum exposure time of seven days to permit a reasonable volume of air to be sampled by the device. This time frame provides a detection limit of 100ppb, determined as three times the standard deviation of F-DNPH measured in blank tubes held at room temperature for seven days. During this time, a saturation level of 4000ppb is determined, using the conservative estimate that only 30% of the trapping reagent is available for reaction with formaldehyde. The passive sampler can provide museum staff with an alternative method of determining accurate concentrations of formaldehyde vapours in artifact enclosures so that possible risks to collections can be assessed. The samplers can also be used in laboratory situations where formaldehyde-containing environments are generated and the correlation between concentration and material damage can be investigated. Although some colorimetric sampling devices have a detection limit similar to the samplers discussed in this study, it is thought advantageous to provide an accurate value for the formaldehyde concentration in air. This will aid laboratory studies that aim to correlate formaldehyde concentration with material damage and assist when comparing formaldehyde concentrations at different locations. Further, the samplers can be used to test materials, either by determination of an equilibrium vapour phase concentration (when the test material is sealed in a closed environment), or by fixing the tube directly onto the surface of the material to determine the emission rate. Several laboratory tests (including the material emission tests) and field applications have been successfully performed with the tube-type sampler, and the results will be reported in a future publication. |
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| ISSN: | ISSN 0039-3630 |
