Losing linearity for copper when extending cal curve ICP-MS DW


I run 200.8 on the 7850 ICPMS for drinking water. 

I calibrate with 10, 50, 100, 250, and 500 ppb for Cu (among others). I would like to calibrate up to 2,000 or higher for Cu - but every time I try to calibrate above 500, my CCV and LFB fail by reading too high (about 115%). 

I measure Ca, Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Pb, and this issue has always been the worst with Cu and Zn

I am so tired of having to dilute half of my samples to get them in the calibration range!!

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