McMillan, N.D., Smith, S.R.P., Bertho, A.C., Morrin, D., O'Neill, M., Tiernan, K., Hammond, J., Barnett, N., Pringuet, P., O'Mongain, E., O'Rourke, B., Riedel, S., Neill, M., Augousti, A., Wüstneck, N., Wüstneck, R., McMillan, D.D.G., Colin, F., Hennerbert, P., Pottecher, G. and Kennedy, D. (2008) Quantitative drop spectroscopy using the drop analyser: theoretical and experimental approach for microvolume applications of non-turbid solutions. Measurement Science and Technology, 19(5), 055601. ISSN (print) 0957-0233

Abstract

The drop analyser, also termed the tensiograph, is an optical fibre-based instrument system for monitoring liquids. A comprehensive assessment of the drop analyser used as a UV–visible spectrophotometer has been undertaken employing both experimental and theoretical studies. A model of the tensiograph signal (tensiotrace) has been developed using a ray-tracing approach to accurately predict the form of the tensiotrace as an aid to drop spectroscopy. An analytical equation is derived for quantitative drop spectroscopy and the form of the equation has been experimentally tested. The equation applies to both the case of a growing drop and the situation in which the drop volume is held stationary. Measurements on both stationary and moving drops are of practical value. Modelling has been used to compute the average path length of the coupled light in the drop to give a result that compares favourably with values obtained from experimental measurements. An optimized method has been identified for quantitative drop spectroscopy measurements. Results from UV–visible studies on both pollutants in water and pharmaceuticals demonstrate the utility of this approach. Two key matters relating to the practicalities of drop spectroscopy are then discussed. Some experimental studies have been made to ascertain the practical limit in analyte concentration above which variations in transmitted light from the drop shape variations result. Here, tabulated information on a representative range of liquid types has been provided as a guide to optimized spectroscopic drop analysis. Secondly, the handling of micro-volume samples is discussed. The paper concludes with a brief evaluation of the usefulness of this drop spectroscopy approach, but specifically points to the importance of drop spectroscopy for nanoscience applications.

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