Species of arsenic found in kriking water include (AsO3)3-, (CH3)2(AsO2)2-, (CH3)AsO3 2-, and (AsO4)3-. Pure water containing no arsenic was spiked with 0.40microgram arsenate/L. Seven replicate determinations gave 0.39, 0.40, 0.38, 0.41, 0.36, 0.35 and 0.39 mcrogram /L.
Find the mean percent recovery of the spike and the concentration detection limit(microgram /L)
May i know how to solve this?
To find the mean percent recovery of the spike and the concentration detection limit, we'll follow these steps:
Step 1: Calculate the mean of the replicate determinations.
Step 2: Calculate the mean percent recovery.
Step 3: Determine the concentration detection limit.
Let's go through each step in detail:
Step 1: Calculate the mean of the replicate determinations.
To find the mean of the replicate determinations, we'll add up all the values and divide by the total number of determinations.
Total sum of replicate determinations = 0.39 + 0.40 + 0.38 + 0.41 + 0.36 + 0.35 + 0.39 = 2.68
Mean = Total sum / Number of determinations = 2.68 / 7 = 0.3828 micrograms/L
Step 2: Calculate the mean percent recovery.
The mean percent recovery can be found by dividing the mean value of the determinations by the spike concentration, and then multiplying by 100 to get it as a percentage.
Mean percent recovery = (Mean / Spike concentration) * 100
Spike concentration = 0.40 micrograms/L (given)
Mean percent recovery = (0.3828 / 0.40) * 100 = 95.7%
So, the mean percent recovery of the spike is 95.7%.
Step 3: Determine the concentration detection limit.
The concentration detection limit can be determined by calculating 3 times the standard deviation (SD) of the replicate determinations.
Standard deviation (SD) = square root of [(Sum of (x - mean)^2) / (n - 1)]
x = individual determinations
mean = mean value calculated in Step 1
n = number of determinations (7 in this case)
Let's calculate standard deviation:
SD = square root of [((0.39 - 0.3828)^2 + (0.40 - 0.3828)^2 + (0.38 - 0.3828)^2 + (0.41 - 0.3828)^2 + (0.36 - 0.3828)^2 + (0.35 - 0.3828)^2 + (0.39 - 0.3828)^2) / (7 - 1)]
= square root of [(0.33 + 0.33 + 0.22 + 0.42 + 0.03 + 0.06 + 0.00) / 6]
= square root of (1.39 / 6)
= square root of 0.2315
≈ 0.481 micrograms/L
The concentration detection limit is calculated as 3 times the standard deviation:
Detection limit = 3 * SD = 3 * 0.481 = 1.443 micrograms/L
So, the concentration detection limit is approximately 1.443 micrograms/L.
To summarize:
- The mean percent recovery of the spike is 95.7%.
- The concentration detection limit is approximately 1.443 micrograms/L.