In clinical biochemistry, analytical and clinical chemistry as well as other science fields, finding the detection limits of materials being analyzed is crucial to accurate results in laboratory testing. The limit of quantitation, or LOQ, is one such limit. LOQ is the lowest concentration that the analyte, or substance undergoing analysis, can be reliably detected in. The three most popular methods for calculating LOQ are: Visual Evaluation, Signal to Noise, and Residual Standard Deviation of the Response and Slope. The latter, Residual Standard Deviation of the Response and Slope, is the most reliable method.
- Graph paper
- Scientific calculator
- Analyte
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Instructions
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1
Make a stock solution of analyte with a specific concentration.
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2
Make a series of standard stock dilutions.
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3
Analyze each solution, beginning with the most diluted and finishing with the stock solution. Record data.
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4
Plot the data using the concentration of the analyte as the independent variable and the peak responses for the dependent variable.
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5
Perform the least squares linear regression of the data.
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6
Calculate the standard deviation (SD) of the y-intercept in relation to the regression line.
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7
Find the average slope of the regression line.
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8
Calculate LOQ using the equation: LOQ = 10 x (SD /m)
Where:
SD = standard deviation
m = average slope of regression line