negative calibration curve FIT R value

Question

Hi All, 
 i have been having an issue with my ICP-MS software as my calibrations are coming back at a negative R value. this is despite full glassware changeover, tubing changed, fresh standards, and ITSD, and doing a thorough wash cycle. 
 the batch tune passes with good counts and RSD. any troubleshooting support to bring my R value to within range would be greatly appreciated.

Tom Herzog · Answer

Hi Katie, 
 You have a Zn contamination issue. Your blank is just under 1 million cps in He mode, should be <1000cps. Your 50 standard (is that ppm?) is over 1 billion cps. Are your samples that high in Zn? Were all of those calibration standards made at the same time? Are they made by serial diution (first the 400ppm is made, then the 200ppm is made from 1/2 dilution of that)? Or do you make all standards from the stock solution individually? Have you checked that the standards were made correctly? That a new stock solution is higher in concentration than what you used to run? 
 What kind of pipette is used? This could be a glassware issue, not the instrument glassware, but your volumetrics used to make standards, or the test tubes you pour them into. It could be in your acid, or the water used to make standards and blank. 
 First thing to try is pull the sample and internal standard line out of solutions and let them go dry. In instrument control, open a new batch and go to the tune tab. Right click in the graph area and click Tune, then Set Acq Parameters for sensitivity. Add masses 66 and 68 in the numerator column and click OK. Start signal monitor, it's an entry right next to the Start AutoTune entry in the toolbar just above the graph area. With it not pumping solution, if mass 66 shows <1000 counts, let it continue to run and see if it will drop lower. This would indicate one or both of your solutions are contaminated. If 66 is very high still, see if mass 68 is just over half the counts of 66. 68 is another Zn peak. If they both show very high counts still, then there is Zn in the system. Clean the cones and lenses to see if that will drop the counts. If on 66 is high, then there is something interfering with that mass. 
 If you can get the mass 66 counts down without solution running, introduce just your water through the sample line. If the counts don't go up, or go up only a little, your water is ok. Next make a solution with 0.5% and 1% of one of the acids used to make your standards, nitric for example . If 1% acid gives twice the counts as the 0.5% acid then that acid lot is contaminated. If you use HCl in your standards, do the same, make a 0.5 and 1% of only HCl and see how the counts compare. 
 Please reply with what you find. 
 Regards, 
 Tom