Performance of high flow permeation tubes releasing SF6. (Abstract)

Abstract

19A Performance of high_flow permeation tubes releasing SF6 R.S. Hegarty1, R.T. Woodgate1 and D.A. Clark 2 1 2 NSW Agriculture Beef Industry Centre, University of New England, Armidale NSW 2351 Dexcel, Private Bag 3221, Hamilton, New Zealand roger.hegarty@agric.nsw.gov.au Ruminal methane production rate can be estimated from the ratio of methane and SF6 in expired air, following administration of an intraruminal permeation tube releasing the inert tracer gas SF6 (Johnson et al. 1994). Release characteristics of such permeation tubes have been well characterised (Lassey et al. 2001) with release rates of 0.61.7 mg SF6/d, leading to SF6 concentrations of 20800 parts per trillion (106�l/l) in samples of expired air. These levels are below the detection limits for infrared spectroscopy, so permeation tubes providing faster delivery of SF6 were developed to achieve higher SF6 concentrations in expired air, able to be measured by a photoacoustic infrared gas analyser. Aluminium bodied tubes able to hold up to 6 g of SF6 were manufactured and loaded with 3.7 g of SF6 for this study. Permeation windows (2.5 cm diameter, 125 �m thick PTFE) were fitted to both ends of the tube, with the PTFE membrane being secured between a 2.5 cm stainless steel sintered frit (2 �m pore size) and a polyvinyl chloride washer. Tubes were cooled in liquid nitrogen, filled with approximately 800 ml of SF6 and sealed. The change in weight of individual tubes was strongly linear (r2 0.9998) for at least 15 d after filling, being approximately 170 mg SF6/d at 39oC. There was no correlation between daily weight loss and time over the experimental period (P>0.05). Comparison of slopes showed the rate of weight loss from the tubes estimated over days 15 and days 615 after manufacture did not differ (P>0.05), although a decline in release rate by approximately 2% over days 615 suggested minor curvature in release rate existed. It is concluded that release rate can be derived from an initial 5 d calibration period prior to insertion into the rumen, but that monitoring of surveillance tubes for longer periods may be warranted if tubes are to be used for prolonged rumen studies. Johnson, K., Huyler, M., Westberg, H., Lamb, B. and Zimmerman, P. (1994). Measurement of methane emissions from ruminant livestock using a SF6 tracer technique. Environmental Science and Technology 28, 359362. Lassey, K.R., Walker, C.F., McMillan, A.M.S. and Ulyatt, M.J. (2001). On the performance of SF6 permeation tubes used in determining methane emission from grazing livestock. Chemosphere Global Change Science 3, 367376. 19 19 19 19 18 18 18 18 18 17 17 17 6 4 2 0 8 6 4 2 0 8 6 4 0 5 000 1 00 0 0 1 500 0 2 00 0 0 o Tube weight (g) 25 00 0 T im e ( m in ) Figure 1 Weight of two .high_flow permeation tubes incubated at 39 C after filling with SF6 . Recent Advances in Animal Nutrition in Australia, Volume 14 (2003)