Q&A ON VALIDATION OF ANALYTICAL PROCEDURES – ICH Q2 GUIDELINE PART -7
Question 1:
What are the possible approaches for determining the detection limit, and what determines their applicability?
Answer 1:
The possible approaches for determining the detection limit depend on whether the procedure is non-instrumental or instrumental. Approaches include visual evaluation and signal-to-noise determination. The applicability of these approaches varies depending on the nature of the analytical procedure.
Question 2:
How the detection limit determined is based on visual evaluation?
Answer 2:
The detection limit based on visual evaluation involves analyzing samples with known concentrations of the analyte and establishing the minimum level at which the analyte can be reliably detected. This method can be used for both non-instrumental and instrumental methods.
Question 3:
What is the basis for determining the detection limit using the signal-to-noise approach?
Answer 3:
The signal-to-noise approach is based on comparing measured signals from samples with known low concentrations of the analyte to those of blank samples. The minimum concentration at which the analyte can be reliably detected is established by determining the signal-to-noise ratio.
Question 4:
What types of analytical procedures are suitable for the signal-to-noise approach?
Answer 4:
The signal-to-noise approach can only be applied to analytical procedures that exhibit baseline noise.
Question 5:
What signal-to-noise ratio is generally considered acceptable for estimating the detection limit?
Answer 5:
A signal-to-noise ratio between 3 or 2:1 is generally considered acceptable for estimating the detection limit.
Question 6:
How is the detection limit (DL) expressed based on the standard deviation of the response and the slope?
Answer 6:
The detection limit (DL) can be expressed as DL = 3.3σ/S, where σ represents the standard deviation of the response and S represents the slope of the calibration curve.
Question 7:
How can the slope (S) for calculating the detection limit be estimated?
Answer 7:
The slope (S) for calculating the detection limit can be estimated from the calibration curve of the analyte.
Question 8:
What are the methods for estimating the standard deviation (σ) for determining the detection limit?
Answer 8:
There are two main methods for estimating the standard deviation (σ) for determining the detection limit:
Based on the Standard Deviation of the Blank: This method involves measuring the magnitude of analytical background response by analyzing blank samples and calculating the standard deviation of these responses.
Based on the Calibration Curve: In this method, a specific calibration curve is studied using samples containing the analyte within the range of the detection limit. The residual standard deviation of a regression line or the standard deviation of y-intercepts of regression lines may be used as the standard deviation.
Question 9:
What data should be presented regarding the detection limit and its determination?
Answer 9:
The detection limit and the method used for determining it should be presented. If the detection limit is determined based on visual evaluation or signal-to-noise ratio, the presentation of relevant chromatograms is considered acceptable for justification.
Question 10:
What is the significance of the value 3.3 in the expression for the detection limit?
Answer 10:
The value 3.3 is a constant used in the formula for calculating the detection limit and is derived from statistical considerations. It represents approximately 99% confidence for a normally distributed response.
