Standards run as Unknown Double what they should be

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

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Hi, I am new to IC so thank you in advance for any responses, they will be greatly appreciated.

I am running a Metrohm 861 Advanced Compact IC with 788 Sample Processor. Software is IC Net 2.3.

Column is a Metrosep A Supp 5-150/4.0. Column is brand new, as in I installed it about two weeks ago (and changed all filters/guards) and ran standards for calibration first.

I calibrated with 17 standards (all made from one base solution with 1000 ppm of all seven elements) ranging from 1 ppm to 500 ppm. Calibration curve looks good, nearly a straight line. RSDs = 3.6 to 5.8, and Corr. = 0.995 to 0.999.

We do not use the IC unit on a daily basis, so every morning a Startup program is run for 45 mins, stepping suppressor 3 times, just to keep it from drying out.

After about a week and a half I ran one a 200 ppm standard (same bottle used for calibration) just to make sure everything was still running ok. It was not...

Results showed 397.9 to 414.9 ppm. A second run of the same sample (same bottle) and got same result. To rule out evaporation of the standard, I made a new fresh 200 ppm solution (different brand, and contains 1000 ppm of 3 elements) and got 405.8 to 454.2 ppm.

As I said, I am new to IC and I do not come from chemistry so I am very confused at this point and don't know what else to check/look for. Peaks are clear (look just like the book, no tailing or extra peaks), baselines are flat, pressure and temperature stay steady once it levels out.

Thank you again, any ideas would be a huge help.
Not enough information to provide an exact cause. Almost anything in the set-up which changed could result in changes. Have you checked for other problems? For example: Do the peaks still elute exactly where they are supposed to (flow rate correct?)? Wrong peak identification = wrong calibration.

However, one other thing to check is that in the sample info area there are settings where you can change the multiplier or dilution values used for the standards. These are normally set to 1.0, but if someone changes them to a higher number the reported values can be multiplied and if they input a dilution value, the output will be reduced.
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