Low concentrations of methylmercury near the detection limit gave the following

Question

Low concentrations of methylmercury near the detection limit gave the following dimensionless instrument readings: 180.3, 145.3, 137.3, 149.3, 194.3, 135. 1, 198. 1, 176.7, 109.7, and 180.5. Ten blanks had a mean reading of 51.5. The slope of the calibration curve is 3.12 times 10^9 M^-1. Estimate the signal and concentration detection limits and the lower limit of quantitation for methylmercury. Number Signal Detection Limit: Number Concentration Detection Limit: M Number Lower Limit of Quantitation: M

Explanation / Answer

Standard deviation from blank reading,

mean of 10 readings = 160.66

variamce = sum (mean - inidividual values)^2/10 = 773.09356

sq.rt.(variance) = standard deviation = 27.804

signal detection limit = 51.5 + 3 x 27.804 = 134.912

concentration detection limit = 3 x 27.804/3.12 x 10^9 = 2.67 x 10^-8

lower limit of quantitation = 10 x 27.804/3.12 x 10^9 = 8.91 x 10^-8

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