I have been having an issue on my 7900 ICPMS where my ISTD recovery will increase or decrease on one sample. It seems to be random and doesn't always fall outside the recovery lines, but sometime will. It is very frustrating when it happens on a calibration point or check standard. We have replaced and cleaned most everything we can (Nebulizer, tubing and lines for autosampler and peripump, ISIS valve head, etc). This issue doesn't occur on our 7800 so I don't believe its something in our samples/standards. It happens sometimes in NoGas mode and other times in He mode. The photos included outline a few instances of it happening. I'm not sure where to look next. I browsed the forum and only saw one thing similar but it was only happening in He mode for them. If anyone has seen this before or has any suggestions, feel free to give them!