ORIGINAL PAPER Andrey Legin Æ Alisa Rudnitskaya Æ David Clapham Boris Seleznev Æ Kevin Lord Æ Yuri Vlasov Electronic tongue for pharmaceutical analytics: quantification of tastes and masking effects Received: 17 May 2004 / Accepted: 22 June 2004 / Published online: 29 July 2004 Ó Springer-Verlag 2004 Abstract The organoleptic aspects of pharmaceutical formulations affect their acceptability to the patient and hence can have an important effect on concordance with treatment. Objective evaluation of these aspects, par- ticularly the taste of the formulation and the drug sub- stance it contains, is difficult. Whilst volunteer taste panels can be used to good effect their utility is limited, particularly during very early stage development when the toxicological profile of the active pharmaceutical ingredient (API) is yet to be established in detail. A potentiometric ‘‘electronic tongue’’ has been applied to analyse a variety of 41 individual substances and mix- tures of particular interest for pharmaceutical research and development. The electronic tongue (ET) was capable of discriminating between substances with dif- ferent taste modalities and could also distinguish dif- ferent substances eliciting the same basic taste; the ET is promising in terms of quantifying the content of each substance and has an ability to detect nuances of the basic taste (e.g. lingering or short-lived). After calibra- tion the electronic tongue was successfully applied to predicting bitterness strength of binary mixtures with a sweetener in terms of ‘‘apparent’’ or ‘‘perceived’’ quinine content. In order to render a formulation palatable it is often necessary to mask the (usually bitter) taste of the API by the addition of masking agents such as sweet- eners and flavours. The ET proved capable of distin- guishing between formulations with different levels of sweetener and/or flavour in a manner that was consis- tent with their masking efficiency as perceived by a small human taste panel. A suitably calibrated ET could have the benefit of providing the pharmaceutical formulator with reliable data concerning the taste of the product quickly and with a reduced need to ask volunteers to taste active pharmaceutical samples. Early development activities could be facilitated when human tasting is usually not possible in the absence of the required toxicological data. Keywords Electronic tongue Æ Pharmaceutical analytics Æ Quantification of taste Introduction Assessment of the taste and flavour of oral drug prep- arations is of major interest to the pharmaceutical industry, particularly for research-based companies. Typical tasks include evaluation of taste changes due to aging, masking of unpleasant (usually bitter) taste of active substances or the selection of the least bitter- tasting molecules from a number of new chemical enti- ties (NCEs). Numerous analytical techniques are routinely used at different drug development and production stages. Determination of the content of various substances that might be relevant to the product quality is usually the aim. Effective and rapid control of flavour and taste characteristics, evidently important for pharmaceutical development, is still a problem. A taste panel, compris- ing specially trained humans, provide for the most reli- able characterization of taste properties. Such an approach has a number of drawbacks: it is slow, expensive, subjective and, in some cases, poorly repro- ducible. The tasting of pharmaceutical preparations is further complicated by ethical restrictions due to the fact that the taste panel has to be exposed to active drugs while being healthy, albeit at levels considerably lower than the therapeutic dose, at least in ‘‘rinse-and-spit’’- type studies. Such human taste-testing can only be A. Legin (&) Æ A. Rudnitskaya Æ B. Seleznev Æ Y. Vlasov Chemistry Department, St. Petersburg University, Universitetskaya nab. 7/9, 199034 St. Petersburg, Russia E-mail: andrew@sensor.chem.lgu.spb.su Fax: +7-812-3282835 D. Clapham GlaxoSmithKline Pharmaceuticals, Harlow, UK K. Lord GlaxoSmithKline Pharmaceuticals, Ware, UK Anal Bioanal Chem (2004) 380: 36–45 DOI 10.1007/s00216-004-2738-3