It is not possible to get negative cps. Negative values are found when subtracting the average of the signal background. Background does not equal its average. Substitute zero for negative values.

Thanks a lot for your help about this issue

While it is not possible to get a negative cps for any signal from the detector (it may give 0 cps but not less than zero), running a blank solution after calibration you may get fewer cps than your original calibration blank for several reasons:

• The calibration blank was not clean (residual material in the instrument, sample tube or acid in the blank solution)
• The Blank sample may be a slightly different matrix (1.4% vs 1.5% HNO3 for example). This may influence spray droplet behaviour or other nebulizer effects.
• Your calibration may not be linear and higher concentrations "drag" subsequent blanks away from the curve.

In any case, an RSD% greater than 10% simply indicates that you have to increase the limit of detection (or limit of quantification or whatever minimum criterion you have chosen to represent the smallest quantifiable concentration) of Chromium you can report.

It simply means that your points of background have more intensity than that part of the subarray responsible for your analyte. Probably there are some interference with another impurity in the blank solution. If the analyte has been contained in the blank, its cps would've never been negative in value, because it is the blank. 10% can mean the absence of the analyte in this blank - and it's obvious.

Good luck! Do your best!

Thank you very much for your interesting comments.

this may be due to interference reaction in the solution