The following minimum specified ranges should be considered:

Drug substance or a finished (drug) product

80 to 120 % of the test concentration

Content uniformity

70 to 130 % of the test concentration

Dissolution testing

+/-20 % over the specified range

Impurity 1 to 120% of the specification

4. Accuracy and PrecisionAccuracy: The degree to which an experimental

result approaches the true or accepted answer

Accuracy – nearness to the truth

.

Ways to Describe Accuracy:

Error: The difference between the result obtained by a method and the true or accepted value.

Absolute Error d = (X – µ)

where: X = the experimental result µ = the true result

All Methods, except counting, contain errors – don’t know “true” value

𝐑𝐞𝐥𝐚𝐭𝐢𝐯𝐞 𝐞𝐫𝐫𝐨𝐫 ሺ%ሻ= 𝐗− µµ 𝐱 𝟏𝟎𝟎

𝐑𝐞𝐜𝐨𝐯𝐞𝐫𝐲 ሺ%ሻ= 𝐗µ 𝐱 𝟏𝟎𝟎

Example

Atomic absorption analysis of As+3 and pb+2 in a sample yield the following resultsAs+3 = 600 µg.ml-1 d = 5 µg. ml-1

pb+2 = 9 µg.ml-1 d = 0.3 µg.ml-1

From absolute error As+3 results is less accurate than pb+2 results but is not true as we see from relative error.

E rel As+3 = 5/600 x100 =0.83% E rel pb+2 = 0.3/9 x100 = 3.3 %

As+3 results is more accurate, although it has larger absolute error.

Several methods of determining accuracy are available:

Drug Substance(authentic sample)

1. Application to an analyte of known purity (e.g. reference material);

2. Comparison with those of a second well-characterized procedure, the accuracy of which is stated and/or defined. (Reference methods)

Drug Product (formulation)

1. Application to synthetic mixtures of the drug product components to which known quantities of the drug substance to be analyzed have been added;

2. In cases where it is impossible to obtain samples of all drug product components, it may be acceptable either to add known quantities of the analyte to the drug product or to compare the results obtained from a second, well characterized procedure, the accuracy of which is stated and/or defined

Impurities (Quantitation)

Accuracy must assessed on samples spiked with known amount of impurities

Accuracy should be assessed

Using a minimum of 9 determinations over a minimum of 3 concentration levels covering the specified range (e.g. 3 concentrations /3 replicates each of the total analytical procedure).

Accuracy should be reported as percent recovery

Precision Precision: The degree to which an experimental

result varies from one determination to the next. Precision - reproducibility

Ways to Describe Precision:

1. Absolute Standard Division

If the results are normally distributed, 68.3 % of the results can be expected to fall within the range of ± 1 σ of the mean as a result of random error.

2. Relative Standard deviation:

3. Confidence limits

We might use this to estimate the probability that the population mean (µ) lies within a certain region centered at

X

Example

A pharmacist determined the % of vitamin C in Rino C Tablets, obtaining the following results, = 15.3 σ = 0.1 n= 4Calculate the confidence limit of the mean at probability90% and 99% (t =2.353 at 90 % probability and, 5.841 at probability 99%)

Solution

µ = 15.3 ± 2.353 x 0.1/√4 µ = 15.3 ± 0.12 µ = 15.3 ± 5.841 x 0.1/√4 µ = 15.3 ± 0.29

Repeatability should be assessed using:

a) A minimum of 9 determinations covering the specified range for the procedure (e.g. 3 concentrations/3 replicates each) or

b) A minimum of 6 determinations at 100% of the test concentration.

Recommended Data:

The standard deviation, relative standard deviation (coefficient of variation) and confidence interval should be reported for each type of precision investigated.

Chromatogram of the same concentration ofNorfloxacin; (a) 5 mg% and the same concentration of

Salicylic acid, (d) 2 mg% id at 274 nm.

Method Validation- LOD and LOQSensitivity

• Limit of detection (LOD) – “the lowest content that canbe measured with reasonable statistical certainty.”

اليقين  من معقولة إحصائية

• Limit of quantitative measurement (LOQ) – “the lowest concentration of an analyte that can be determined with acceptable precision (repeatability) and accuracy under the stated conditions of the test.”

How low can you go?

Detection Limit

smallest concentration which can be reported with a specified degree of certainty by a definite, complete analytical procedure.

Methods of determination(depending on whether the procedure is a non-

instrumental or instrumental.)

Based on: 1. Visual Evaluation2. Signal-to-Noise3. The Standard Deviation of the Response and the

Slope a) the Standard Deviation of the Blank b) the Calibration Curve

Based on Visual EvaluationIs determined by the analysis of samples with known concentrations of analyte and by establishing the minimum level at which the analyte can be reliably detected.

Signal-to-NoiseTypically 3 times the signal-to-noise (based on standard deviation of the noise) موجات تداخل

The Standard Deviation of the Response and the Slope

The detection limit (DL) may be expressed as: DL = 3.3 σ/S

• σ = the standard deviation of the response• S = the slope of the calibration curve

• The slope S may be estimated from the calibration curve of the analyte. The estimate of σ may be carried out in a variety of ways, for example:– Based on the Standard Deviation of the Blank – Based on the Calibration Curve

Quantitation limit

The minimum level at which the analyte can be quantified with acceptable accuracy and precision.

Based on Signal-to-Noise Approach Typically 10 times the signal-to-noise (based on standard deviation of the noise)

Based on the Standard Deviation of the Response and the Slope The quantization limit (QL) may be expressed as: QL = 10σ/ S Where

s= the standard deviation of the response S = the slope of the calibration curve The slope S may be estimated from the calibration curve of the analyte.

The slope S may be estimated from the calibration curve of the analyte. The estimate of σ may be carried out in a variety of ways, for example:– Based on the Standard Deviation of the Blank – Based on the Calibration Curve

Robustness

Robustness of an analytical procedure is a measure of its capacity to remain unaffected by small but deliberate variations in method parameters. It should show the reliability during its usage.

Examples of typical variations are:

1. stability of analytical solutions, 2. extraction time.

Examples In the case of liquid chromatography, 1. variations of pH in a mobile phase2. variations in mobile phase composition, 3. different columns (different lots and/or suppliers), 4. temperature, 5. flow rate.

In the case of gas-chromatography, examples of typical variations are different columns, temperature, flow rate.

RuggednessRuggedness of an analytical method is the degree

of reproducibility of the results obtained by the analysis of the same sample under a variety of normal test conditions.

For example different laboratory,analysts, instruments, and reagents.

System suitability testing

• The tests are based on the concept that the equipment, electronics, analytical operations and samples to be analyzed constitutes an integral system that can be evaluated as such.

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