Why are there negative concentration values in the data? What do they mean?
In principle,THERE IS NO SUCH THING AS NEGATIVE CONCENTRATION. However instrumental responses/readings can have such due to matrix effect or improper way of reading the sample. The sample matrix may have significantly different matrix from your CALIBRATION BLANK. You must always remember that your sample must have a lowest concentration reading equal to or higher than your calibration blank considering the fact that your instrument is not defective and your reagents were properly prepared and not yet exceeded its shelf life.
A negative concentration value indicates that the sample was analyzed but that the concentration was below the determination limits of the analytical method. All instrumental methods for analyzing the concentrations of various elements in sediments, waters, rocks, or plants have lower determination limits. Concentrations below this lower determination limit are too small to be detected by the method. For example, one of the Oak Ridge Multielement Emission Spectrochemical Analysis methods could not detect concentrations of silver (Ag) that were less than 2 parts-per-million (ppm). When the analytical method determined that a sample contained less than 2 ppm Ag, a value of “-2” was recorded in the Ag_ppm field. Unfortunately, we don’t know if that means that the sample contains 1.8 ppm Ag or 0.0001 ppm Ag. The best that can be said is that the concentration is <2 ppm Ag. Some analytical methods record different negative numbers for an element in successive samples. For example, undetecte
