Low concentration replicate samples of Cd-EDTA gave the following counts in a mass spectral measurement: 178.3, 131.2, 144.3, 159.3, 128.3, 197.7, 149.3, 153.9, 143.3, 160.9. Ten measurements of a blank had a mean of 27.7 counts. A sample containing 2.00 ?M Cd-EDTA gave 1543 counts. Estimate the signal detection limit for Cd-EDTA.