1. System Suitability โRSD Requirement
Basic understanding of calculation, Current practice and regulatory requirement
C. P. SINGH
Research Scientist โ ARD
2. Replicate injections of a standard preparation or other standard solutions are compared to ascertain
whether requirements for precision are met.
Unless otherwise specified in the individual monograph, data from five replicate injections of the
analyte are used to calculate the relative standard deviation (RSD), if the requirement is โค2.0%;
data from six replicate injections are used if the RSD requirement is >2.0%.
System Suitability - RSD
3. %๐๐๐ =
๐๐ ๐ง
๐ญ ๐๐%, ๐ง โ ๐
For the assay in a drug substance monograph, where the value is 100% for the pure substance, and no
maximum RSD is stated, the maximum permitted %RSD is calculated for a series of injections of the
reference solution:
System Suitability - RSD
Where:
K is a constant (0.349);
B is the upper limit given in the definition of the individual
monograph โ 100%;
n is the number of replicate injections of the reference
solution (3 โค n โค 6);
t90%,nโ1 is the Studentโs t at the 90% probability level
(double sided) with nโ1 degrees of freedom.
RSD Requirement
B (%)
Number of individual injections
3 4 5 6
Maximum Permitted RSD
2.0 0.41 0.59 0.73 0.85
2.5 0.52 0.74 0.92 1.06
3.0 0.62 0.89 1.10 1.27
Unless otherwise prescribed, the maximum permitted RSD does not exceed the appropriate value given
in Table of repeatability requirements. This requirement does not apply to tests for related substance.
4. ๐น๐๐๐๐ข๐๐
๐ก ๐๐๐ ๐ก๐๐ข๐๐๐ก๐๐๐ = 1 โ ฮฑ/2
Example
๐ก ๐๐๐ ๐ก๐๐ข๐๐๐ก๐๐๐ for 90% probability
level (double sided)
Step - 1:
100% โ 90% = 10%
Step โ 2:
ฮฑ = 10/100 = 0.1
Step โ 3:
๐ก ๐๐๐ ๐ก๐๐ข๐๐๐ก๐๐๐ = 1 โ
0.1
2
= 0.95
How to calculate t distribution value for student t table using t table
How to calculate degrees of
freedom
Degrees of freedom (d.f.) = nโ1
Example
For six replicate injection,
d.f = n-1 = 6-1 = 5
5. T.INV.2T function
Returns the two-tailed inverse of the Student's t-distribution.
Syntax
T.INV.2T(probability,deg_freedom)
The T.INV.2T function syntax has the following arguments:
โขProbability Required. The probability associated with the Student's t-distribution.
โขDeg_freedom Required. The number of degrees of freedom with which to characterize the distribution.
How to calculate probability
90% probability level (double sided)
Step - 1:
100% โ 90% = 10%
Step โ 2:
ฮฑ = 10/100 = 0.1
How to calculate degrees of freedom
Degrees of freedom (d.f.) = nโ1
Example
For six replicate injection,
d.f = n-1 = 6-1 = 5
How to calculate t distribution value for student t table using MS excel