Amperometry can be applied to the analysis of dopamine, a hormone and neurotransmitter. Signals from six replicate samples with a concentration close to three times the detection limit were 1.26, 1.18, 1.13, 1.12, 1.22, and 1.11 nA . The average signal for ten reagent blanks was 0.17 nA . What is the signal detection limit ?