Martin, We use dual inlet IRMS here. We prepare our atmospheric nitrogen standard offline using a pyrex/quartz prepline, similar to that in the 1975 paper by Charles Kreitler. We run the air sample first through a quartz copper oxide furnace at 700 degrees C, then through a pyrex copper oven at 400 degrees C. Our comparisons during an interlaboratory study was very good. Glen Martin Water Sciences Laboratory 103 NRH, East Campus University of Nebraska Lincoln, NE 68583-0844 voice: 402-472-8210 FAX: 402-472-9599