High RSD in O2 mode on 8900

Recently an issue has come up with RSD being high 25-50% in O2 mode for P and S. The RSD's are high for Sc internal standard 45-45 in O2 mode as well.

All other elements and internal standards have very good RSD.

The O2 tank is 99.999% and hasn't been changed since this started.

There is an odd pattern with the 4 P and S replicates, where #1 and #4 are high and agree, and #2 and #3 are low and agree.

The pump tubing is new, the cones look good, the nebulizer/chamber/torch are all clean.

Any ideas on this strange pattern?


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