analysis for potassium by atomic absorption spectroscopy yielded a detector signal (proportional to concentration) of 110.2 when a sample was aspirated into the plasma and 0.7 when water (i.e. blank) was aspirated. after a small amount of nacl was dissolved in the sample, the detector signal increased to 133.6 when the sample was aspirated whereas the blank measurement remained at 0.7. what is the most likely cause of the increased detector signal?