In today's blog article we want to deal with calibration, instrument and method qualification as well as method validation and define these terms against each other.
Within the pharmaceutical industry, analytical instruments are used for specific analysis of drug substances (DS) and / or drug products (DP). To control the quality, a regular confirmation test to demonstrate the instrument’s capability for the intended use is performed. This process is called calibration. It should not be mixed with the system suitability test (SST), which is performed each time the method is done. Calibration can be explained as a process by which the correct performance of an instrument is ensured. The performance of an instrument may vary because of multitude of reasons such as fluctuations in the environment or its ageing components.
Differences in performance may also be seen during servicing of the instrument or replacement of its components. During calibration the performance of the instrument is checked using reference material and in case a deviation is noticed the instrument is adjusted to the correct value. For a laboratory to ensure quality system, it is mandatory to minimize these variations and hence a periodical calibration procedure is applied. For this, the periods may vary from daily (like pH meters) to monthly (e.g. balances every 3-6 month) or yearly (e.g. photometers), depending on how often the instrument is used and which criticality the instrument is assigned to.
Traditionally, there are two existing concepts for calibration processes that laboratories can choose from:
- All instruments and equipment are calibrated.
- The calibration procedure is applied only to instruments capable of physical measurements, and where the output is a direct measurement of a traceable physical parameter. For example, balances, spectrometers, thermometers, etc. may be calibrated because there are standards available to determine the uncertainty of the measurements. For others, only performance verification can be performed in the laboratory. For example, for an HPLC system, the performance is maintained within a set of predetermined criteria to ensure the quality and consistency of the generated data. Typical features include injector precision, flow rate accuracy, gradient accuracy, detector response, etc.
Calibration is an integral part of the quality system and is required to follow according to a previously defined Standard Operating Procedure (SOP).
A very simple example is the daily calibration of a pH meter, where the pH of two reference standard solutions (e.g. pH 4 and 9) is measured, small differences in the obtained values are observed and then the machine is accordingly adjusted to show 4 or 9 as true values.
Analytical Instrument qualification (AIQ) is not just a single step process but a collection of different processes. A very good description is provided in the United States Pharmacopoeia (USP) chapter <1058>. AIQ is mainly comprised of 4 categories:
1. Design Qualification (DQ)
Design qualification (DQ) is the documented collection of activities that define the functional and operational specifications of the instrument and criteria for selection of the vendor, based on the intended purpose of the instrument. It can be regarded as the planning phase of the requirements to be applied for a specific instrument. DQ should be performed both by the developer and the user. The developer must design and manufacture the instrument as per the user requirements specification (URS), if possible in a quality control environment. The user on the other hand, can justify the selection of the vendor based on method selection and intended use of the instrument and the compliance of the vendor to the specifications set by the user. DQ ensures that instruments have all the necessary functions that can be successfully implemented for the intended purpose. DQ makes sense for big instruments or machines used in production, for a simple microscope it might be a little bit too much ;-)
2. Installation Qualification (IQ)
Installation qualification (IQ) is the documented collection of activities necessary to establish that an instrument is delivered as designed and specified (by a comparison of the URS against the reality), is properly installed in the selected environment, and that this environment is suitable for the instrument. IQ allows user responsibility to ensure proper installation of the instrument with direct support from the vendor. IQ requires the user to establish and maintaining appropriate working environment, but on the other side it allows the identification of any instrumental damage or any variation from the placed order. Let’s illustrate this with an example. Imagine a lab where a new fluorescence microscope has been bought. During IQ, the microscope is situated at its predefined place, all cables are connected, the software is installed, all documents like e.g. the user manual are handed over and it is switched on for the first time.
3. Operational Qualification (OQ)
Operational Qualification (OQ) is a documented collection of activities required to demonstrate that an instrument will generally function according to its operational specification in a defined environment. According to the USP, “Users, or their qualified designees, should perform these tests to verify that the instrument meets manufacturer or user specifications in the user’s environment. Designees could be, for example, vendor representatives.” It is important to test the instrument at the user’s defined environment because mechanical damage is possible during transport and installation that may affect the performance of the instrument. This step can also include a first calibration of the instrument and a training by the vendor of the personal which will work with the new instrument. For our microscope example, in OQ the general ability to visualize fluorescent staining is checked, e.g. by checking a slide with fixed cells stained with Cyber green. This is some kind of unspecific and not yet related to any routine test.
4. Performance Qualification (PQ)
Performance Qualification (PQ) is the documented collection of activities necessary to demonstrate that an instrument consistently performs according to the specifications defined by the user and is appropriate for the intended use. PQ emphasises on consistent performance by regular maintenance and testing. Although, the PQ and OQ appear very similar, there are distinct differences between the two. PQ is performed more frequently than OQ and is done under similar conditions that are for routine analysis. In our example, in the PQ a routine test like the comet assay to detect DNA damage for which previously silver stained samples have been used is now performed and analysed applying fluorescence staining to be visualized using the new microscope. Using a sample with known damage (already analysed with silver staining), can the new microscope be proven to show the same result?
Analytical Method Qualification (AMQ)
Analytical procedures are mandatory for analysis of specific drug substances (DS) and drug products (DP). Qualification of analytical method simply suggest its suitability for the intended use. An AMQ needs laboratories to specify the working parameters over which the method will perform and requires them to confirm the performance as per pre-defined acceptance criteria using available reference standards. AMQs are usually performed at the early (pre-clinical) studies when compared to analytical method validation, but can also be done later before a normal validation e.g. in the development department to have first ideas about how the method is performing.
It is essential to qualify an analytical method at the earlier stages of a pre-clinical development. Although, both method qualification and method validation certify the suitability of the method, they differ in the robustness and the depth of the studies. Qualifications are generally smaller in scope than validations, less dynamic and often a smaller group of a larger validation initiative. At the early stages of the development, qualification could be a choice but towards the later stages, validation is mandatory, without which, no application for approval will be accepted.
It is possible (not necessary) for companies to straightway go for the validation and skip the qualification all together. It happens for example, during the development of a generic drug substance, where the chemical equivalence is required to be proven. Because of the cost factor, many companies choose to perform the qualification at the early stages and continue with validation when it is required for later stages of clinical trials or commercialization.
Like method qualification, also method validation is a process that confirms the suitability of in-house developed methods for their intended analytical use. Results obtained through the validation are used to judge the quality, reliability and consistency of any analytical method. There are regulatory requirements regarding the parameters to be analysed during validation which may differ according to the type of method. The most important guideline is the ICH Q2(R1). More information about method validation can be found here and here.