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HPLC USP Methods

Adjustments - Adjustments according to USP Chapter 621

Users from the regulated environment (e.g. the pharmaceutical industry) are often bound to so-called monograph methods of the European or US Pharmacopoeia(Ph. Eur. or USP). The specifications laid down in the pharmacopoeias for the analysis of the substances to be analysed must be followed. These are mainly laid down in Chapter 621 of the USP.

Chapter 621 of the USP expressly contains practical recommendations that allow deviations from the specifications of the method in a monograph without requiring a revalidation of the method. The adjustment is considered necessary for the fulfilment of the system suitability test (SST) criteria. The following tables provide an overview of the parameters that can be varied and the limits permitted in each case.

The following parameters may be adjusted for both isocratic and gradient separations:

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ParametersPermitted deviation*
Packing materialAny (as long as SST criteria are met and the column category (LXX) remains the same ("remaining same chemistry")
Injection volumeAny (as long as SST criteria are met)
Column temperature+/- 10 °C
pH value Mobile phase+/- 0.2 pH units
Salt concentration in buffer / buffer strength+/- 10%
Eluent composition

The adjustments apply to the sub-component of the mobile phase (≤50%). The content of these components may be adjusted by +/- 30% (relative). However, the change for each component must not exceed 10% absolute (relative to 100% of the mobile phase).
The following examples from Chapter 621 of the USP illustrate this:

  1. The eluent composition is 50:50.
    30% of 50 is 15% absolute. This exceeds the permitted absolute deviation of 10%. An adjustment is therefore permitted here in the range from 40:60 to 60:40.
  2. The eluent composition is 2:98.
    30% of 2 is 0.6% absolute. The maximum permitted adjustment here is therefore in the range from 1.4:98.6 to 2.6:97.4.
  3. The eluent composition is 60:35:5.
    For the second component: 30% of 35 is 10.5% absolute. This exceeds the permitted absolute deviation of 10%. Component 2 can therefore only be varied in the range from 25% to 45% absolute.

For the third component: 30% of 5 is 1.5% absolute. The following adjustments therefore fulfil the requirements here: 50:45:5 to 70:25:5 or 58.5:35:6.5 to 61.5:35:3.5.

The following parameters may only be adjusted for isocratic separations:

ParametersPermitted deviation*
Flow velocity (F)(1.) +/- 50%
or
(2.) A flow change that is adapted to a change in column length, internal diameter and particle size, see below.
Column length (L) / particle size (dp)A change is permitted so that the new quotient L/dp corresponds to a value between -25% and 50% of the value of the original quotient.
Alternatively, other quotients (L/dp) can also be used as long as the theoretical base number N has a value between -25% and 50% of the original quotient.
Flow velocity (F) / particle size (dp)

If the particle size is changed, the flow velocity must be adjusted, as smaller particles require higher linear flow velocities to achieve the same performance (determined by the theoretical plate number).
The following formula can be used to calculate the new flow when the internal diameter and particle size are changed.

F2 = F1 x [(dc22 x dp1)/(dc12 x dp2)]

F1...Original flow velocity
F2...New flow velocity
dc1...Internal column diameter of the original column
dc2...Internal column diameter of the new column
dp1...Original particle size
dp2...New particle size

If the original particle size is ≥ 3 μm and the new < 3 μm, the flow must be adjusted accordingly so that the plate number does not decrease by more than 20%.

Column IDCan be adjusted as required, provided that the linear flow rate remains constant.
Injection volumeAny (as long as SST criteria are met)

* Modifications outside the specified limits are considered "changes" that require revalidation of the method used

The wavelength of the UV/VIS detector must not be changed. It must be ensured that the absolute error when setting the wavelength does not exceed +/- 3 nm.

For more detailed information, see the adjacent information from the USP. ->

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