ANALYTICAL & LAB EQUIPMENT
QUALIFYING
INSTRUMENTS Exploring the facilitated qualification of liquid chromatography instruments using a new continuous digital flow meter
Figure 2. The Biotech Liquid Flow Meter for facilitated flow monitoring and instrument qualification
Q
ualification procedures for liquid chromatography instruments (HPLC & UHPLC) are designed to
ensure that the analysis instruments work correctly and thus generate consistent and valid analytical results. An incorrect flow rate will inevitably affect substance retention times and chromatographic peak area integration, which in turn influence the accuracy of quantitative results, especially if the flow rate is unstable. Instrument qualification tests have
been defined [1] by the European Network of Control Laboratories (GEON), which is coordinated by the European Directorate for the Quality of Medicines & HealthCare (EDQM). Laboratories accredited according to ISO/IEC 17025 are required to implement these quality assurance procedures, although others aiming to provide high quality products and services, can certainly also benefit from similar efforts to ensure that trustworthy analysis results are continuously generated. Similar guidelines have been issued [2] by the United States Pharmacopeia (USP) as part of its general chapter <1058> which currently is under revision. The periodic checks mentioned in
the equipment qualification guidelines for instrument modules (“Level III”) [1]
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issued by GEON, include experiments to verify that the flow rate is accurate [1,3], together with practical examples of how data could be gathered. The assessments involve ensuring that the absolute flow rate is within a suggested ±5% of the set value for HPLC instruments, and within ±3% for UHPLC systems. The typical acceptance limit for flow rate precision has been set to ≤0.5% relative standard deviation (RSD) for these tests. In essence, this corresponds to the operational qualification (OQ) in the USP nomenclature [2]. Traditionally, the liquid flow rate
was measured by collecting the exit liquid while simultaneously recording the gathering time [3]. The collected liquid was then determined either volumetrically or gravimetrically, making these methods inherently manual and labour intensive. Previous digital liquid flow meters have mainly automated the volumetric measurement approach, and such devices have integration times ranging from tenths of seconds up to one minute at typical liquid chromatography flow rates (0.2 - 1 mL/min).
Figure 1. The measurement principle of a thermal flow sensor
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