According USP Chapter 621 : Adjustment of Mobile Phase

Adjustment of Mobile Phase

Adjustment in composition of the mobile phase

Adjustment ph of the aqueous component of the mobile phase

Adjustment in concentration of salts in the buffer component of a mobile phase

Adjustment in composition of the mobile phase

1. Minor compound of the mobile phase can be adjusted by +- 30 % Relative
2. Change in any component cannot exceed +- 10 absolute

-Example of Binary mixture

– Example of temany mixture

-Example of Binary mixture

1. Eg 1:  Ratio MP (80:20)

Minor solvent Ethanol

How much will be allowed adjustment EtOH ?

Calculated 30 % of 20

30*20/100=6

Identified which one is lower, either 30 % relative or +-10 absolute of minor component (EtOH)

30% of EtOH (6%) Is smaller than absolute 10 %

First component to give total 100%

MP composition Water: EtOH 86:14  with Relative -30 % EtOH change EtOH

MP composition  Water : EtOH 74:26 with Relative + 30% EtOH change EtOH

Eg 2:  Ratio MP (60:40)

Minor solvent Ethanol

How much will be allowed adjustment EtOH ?

Calculated 30 % of 40

30*40/100 = 12

Identified which one is lower, either 30 % relative or +-10 absolute of minor component (EtOH)

30% of EtOH (6%) Is More than absolute 10 %

First component to give total 100%

MP composition Water: EtOH 70:30  with Relative -30 % EtOH change EtOH

MP composition  Water : EtOH 50:50 with Relative + 30% EtOH change EtOH

Termary Mixture

Ratio 70:25:5

EX:1  calculate 30 % variation for 2nd component

30*25/100 = 7.5

Identified which one is lower ether 30 % or +-10

30% 2nd component to give 7.5%  is lower than absolute 10%

Use component to give  a total 100 %

MP composition 77.5:17.5:5 with 2nd  component -30% absolute change

MP composition 62.5:32.5:5 with 2nd component +30% absolute

EX:2  calculate 30 % variation for 3nd component

Ratio 70:25:5

30*5/100 = 1.5

Identified which one is lower ether 30 % or +-10

30% 3nd component to give 1.5 %  is lower than absolute 10%

Use component to give  a total 100 %

MP composition 71.5:25:3.5 with 2nd  component -30% absolute change

MP composition 68.5:25:6.5 with 2nd component +30% absolute

PH adjustment in Mobile phase

+- 2  variation acceptable

Eg: Mobile phase ph  5.0

Taken ph 4.8 to 5.2

Adjustment of concentration of buffer +- 10 %

Eg buffer weight (KHPO4) is 20gm

Allow to 18g to 22 g