Sub-headings within the method together with a table of contents can aid review for lengthier methods. Sub-headings could include, as applicable:
1 Introduction
2 Apparatus
3 Reagents and Standards
4 Samples
5 Procedure
5.1 Reagents and Standards Preparation
5.2 Sample Preparation
5.3 Instrument Settings
5.4 System Suitability Tests
5.5 Test Procedure
6 Calculations
7 Reporting
8 Chromatograms
Information generally required for each of these sections is provided in the sub-sections below.
Where there is excessive data (e.g. for novel or non-compendial excipients), additional data may be included in 3.2.A.3 Excipients section.
1. Introduction
The method introduction should include a brief description of what is being determined and how it is being tested together with the compendial reference if applicable, e.g. The water content of [drug substance] is determined by coulometric Karl Fischer titration and complies with USP<921> Water Determination.
For UK/EU markets, this statement should suffice for compendial methods. US submission will usually require a brief summary of the method to include any critical attributes.
2. Apparatus
The main apparatus should be listed but standard laboratory equipment such as weighing scales, flasks, pipettes do not need to be included. Typically, it is also not necessary to include makes and models of equipment unless this is critical to the method e.g. it is generally acceptable to state ‘High Performance Liquid Chromatography (HPLC) system’ without further detail. Where feasible HPLC columns can be described generically (without the need to specify make and model). Consider including ‘or equivalent’ after equipment to allow flexibility for like for like substitution, as might be required at a later date. This approach can reduce the need for unnecessary regulatory submissions for minor changes.
3. Reagents and Standards
Reagents and standards are best presented in a list and should include the analytical grade of each material e.g. Ph. Eur. grade. Quantities for each material generally need not be included and this allows flexibility to change quantities as needed, possibly without the requirement for a further regulatory submissions.
4. Samples
Samples may be listed without the need to specify the quantity required. This also allows flexibility to change quantities as needed, possibly without the requirement for further regulatory submissions.
5. Procedure
5.1 Reagents and standards preparation
Preparation of reagents and standards should generally be provided. These can sometimes be provided without the need to detail dilution steps, nor specific weights or volumes (see examples below). This allows flexibility to change weights and volumes as needed, without the requirement for a regulatory submission. e.g.:
Prepare a blank sample of 50 mM ammonium acetate:acetonitrile, 30:70%v/v.
Prepare a 1N NaCl solution.
Prepare a sample solution containing 10 mg/ml of [sample] in water.
It is also generally not necessary to state the standard laboratory equipment used to prepare reagents and standards unless the equipment is critical to the method e.g. no need to refer to weighing bottles, flasks, pipettes.
5.2 Sample Preparation
The same level of detail used for reagents and standards can also be applied to the preparation of samples.
5.3 Instrumental Settings
For more complex methods such as high performance liquid chromatography (HPLC) and gas chromatography (GC), it may be necessary to include equipment settings. These can be included in a tabulated form and typically should only include the critical . Reference can also be made to these being ‘example conditions’ to allow flexibility to make noncritical adjustments as necessary.
5.4 System Suitability Tests (SST)
All critical system suitability tests should be briefly described in this section together with calculations where necessary.
5.5 Test Procedure
A brief description of the sample analysis can be included. This should only contain critical details. Where duplicate or multiple runs are performed, consideration should be given to whether this level or detail is necessary to include in the regulatory method. Not specifying this level of detail may avoid unnecessary regulatory changes at a later date, should the number of runs need to be amended. It may be enough to state, for example: ‘Analyse the samples. Determine the concentration of [residual solvent] according to section x Calculations’.
6. Calculations
Unless simple and obvious, calculations should be included. These should be clearly presented and state the units of measurement for each element within the calculation. An example is provided in the equation below.
7. Reporting
This section should detail how the results are reported, together with units of measurement and number of decimal places, as applicable. The reporting should align with the acceptance criteria presented in the specifications section. Where applicable, reporting may need to include reference to “ND” (not detected), “Fail”, “NMT” (not more than) or “NLT” (Not Less Than) etc., as applicable to the acceptance criteria in the specifications.
8. Chromatograms
For methods where spectra and chromatograms are generated, it is prudent to include example chromatograms for each sample, standard, and blank. These should be legible, with axes and peaks clearly labelled.
