Performance qualification of an electronic tongue based on ICH guideline Q2

Recent progress in sensor technology has led to the development and application of electronic taste sensing systems. Especially taste prediction of pharmaceutical formulations is a matter of particular interest and is increasingly performed using electronic tongues. Several studies have dealt with electronic tongues before, but an analytical approach describing successfully conducted qualification has not been reported yet. Performance qualification of the taste sensing system SA402B (Insent Inc., Atsugi-chi, Japan) equipped with seven lipid membrane sensors was undertaken with special regard to bitter taste assessment. These sensors represent the gustatory stimuli bitterness, umami, saltiness, sourness, and the nociceptive sensation astringency. Specificity, linearity, range, accuracy, precision, detection and quantitation limit as well as robustness were established for each sensor type referring to ICH guideline Q2 (R1). Some items mentioned in the guideline were applicable whereas others had to be modified due to differences of the system to other commonly used analytical techniques. Quinine hydrochloride being one of the bitterest drugs served as model substance. A large range of linearity (0.01-100mM) with corresponding precision (RSD<4%) was found for most sensors. One sensor had a lower detection threshold (0.0025mM) for quinine hydrochloride than humans typically have. Different methods for determination of detection and quantitation limits were implemented and discussed with respect to rationality and feasibility. Therefore the approach based on visual evaluation was found as most adequate. An adapted guidance following ICH guideline Q2 was developed serving qualification of taste sensing systems in the future.