System Suitability is a measurement scale for confirmation as respective used system is suitable for particular analysis and give accurate measurement.
Chromatograms of LOQ
If all the System Suitability parameters meet the acceptance criteria of system suitability, the generated results will be authentic and valid.
Suitability of system is monitored during chromatography analysis by considering following parameters:-
1- Symmetry factor:- As per USP chapter 621 (Chromatography) the symmetry factor is also known as asymmetry or Tailing factor. The purpose for calculating symmetry factor to know the Symmetrical shape of peak.
The formula to calculate symmetry factor is :-
W0.05
As = ---------------
2d
Where
W0.05 = width of the peak at 1/20th of peak height.
d = Distance between perpendicular drop from peak maximum and the leading edge of the peak at 1/20th of peak height.
2- Theoretical plates:- Theoretical plates represent to column efficiency.
The concept of Theoretical plates was adopted by Martin and Synge in 1941 based on distillation column which was used in refining of crude petroleum.
Theoretical plates are not a real plates in column it is only a hypothetical zone where equilibration being done in mobile phase and stationary phase. And sample also being equilibrated along with mobile phase. We can understand as one plate represent to one equilibration of sample component between mobile phase and stationary phase.
We can understand the concept of Theoretical plates with a simple example of stairs. To move for next floor we used stairs. If there is only 15 stairs and every stairs have much hight then we have to stretch our legs too much according to hight of stairs. But we reduce the height of stairs then definitely the number of stairs will increase but it will be easy to us and comfortable also during movement on next floor.
The same thing happened with theoretical plates. Much equilibration gives More plates and make the overall separation process simpler.
I think It must be clear now that no such plates exist in reality in the chromatographic columns. You just have to imagine that your column is divided into a number of sections or plates. As stated earlier, a sample component spends a finite time in each plate as it moves the column length and this is the time required to establish equilibrium over the length of the plate between its concentration in the stationary phase and the mobile phase.
In simple terms, it can be stated that a theoretical plate represents the distance that is needed for every adsorption-desorption step. The movement of the analyte is assumed from plate to plate as a series of equilibrated mobile phase plugs. In other words, the greater the number of such plates, the more efficient is the separation power of the column.
Theoretical plates can be calculated by following formulas:-
N= 5.54 (tR / w0.5)2
Where tR = retention time.
w0.5 = width at half height.
Another formula is used as
N= 16 (tR / wb)2
Where wb is width at base.
3- Resolution:- When a solution having mixture of two components and same passes through column, both components eluted at different retention time. If both peaks are properly seperated then resolution can be measured between both peaks.
The formula for resolution is as:-
Rs= (1.18)x (RT1- RT2 )/ 0.5 (W1-W2)
Where is
RT1 and RT2 = retention time of first peak and second peak respectively.
(W1-W2) = width of peak 1and peak 2 at base.
4- Similarly factor:- Similarly factor calculated to check any weighing error of standard weight.
Two standard to be prepared seperately and injected the same. The formula of similarity factor is as:-
Area of STD A x Wt. of STD B
S.F.=--------------------------------------
Area of STD B x Wt. of STD A
5- Signal to Noise ratio:- The signal to noise ratio parameters are monitored in LOQ solutions. The purpose of this parameter to find out the signal response against noise level of baseline.
To determine the noise ratio, atleast one blank and one LOQ solution to be injected.
The formula for signal to noise ratio is as:-
S/N = (2H/h)
Where in H = height of analytical peak in LOQ solution.
h= range of noise in blank injection.
Chromatograms of blank.
6- % RSD of retention time:- The retention time of analytical peak should be consistent. The relative standard deviations can be calculated by using following formulas:-
%RSD= (SDx100)/ Average
___________
SD= √ Σ (xi-x`)2
-----------------
N-1
Here is a example for calculating standard deviations. Let's assume we have to find % RSD of number 51, 38, 79, 46, 57. So below are the steps to calculate SD.
1- Find the mean value of these numbers.
( 51+38+79+46+57)/5 = 54.2
2- Find the square difference from the mean i.e. ( Valve- mean value)2
_____________________________
√ ( 51-54.2)2 + (38- 54.2)2 + (79- 54.2)2 + ( 46- 54.2)2 + ( 57- 54.2)2
= -------------------------------------------
5-1
_____________________________
√ 10.24+ 262.44+ 615.04+ 67.24+ 7.84
--------------------------------------------
4
____________________
= √ 962/ 4
_______________
= √ 240.7
SD= 15.51
%RSD = (15.51 x 100)/ 54.2
= 28.6%
7- %RSD of Area:- The area of analytical peak should be consistent. The % RSD for area is can be calculate by using below formula i.e.
%RSD= (SDx100)/ Average.
8- p/v ratio :- p/v ratio is called as peak to valley ratio. This parameter is used in such case where it is confirmed as peak separation can not be achieved between known two adjacent peak. The following formulas can be use for calculating p/v ratio:-
p/v = Hp/ Hv
Where is Hp= height above extrapolated baseline Of the minor peak.
Hv = height above the extrapolated baseline at lowest point of curve seperating the minor and major peak.
Abhishek Singh is the author of Pharma technical support. He is pharmaceutical professionals, having experience of more than 12 years in Quality.