Low-Temperature Thermal Decomposition of Sulfates to SO2 for On-Line 34S/32S Analysis

We describe a fast, inexpensive, and safe method of direct SO(2) extraction from BaSO(4) for sulfur isotopic analysis by mass spectrometry. Only two reagents are used: (1) pure NaPO(3), which is mixed with BaSO(4) sample, and (2) Cu foil, from which reaction boats are manufactured. The extraction precedes in the Cu boat placed into a quartz tube connected to a vacuum line. The boat is heated to 650-700 °C while pure SO(2) produced is collected in a "cold finger". Reaction is complete in 7-10 min. We have proven by means of (18)O-enriched BaSO(4) specimens that the oxygen isotopic composition of the SO(2) is totally controlled by (18)O content in NaPO(3), when the weight ratio of the reagent to sample exceeds 6:1. The method described can be used for "on-line" SO(2) preparation for isotopic analysis.