• Robert De Levie

      Articles written in Journal of Chemical Sciences

    • Spectrometric mixture analysis: An unexpected wrinkle

      Robert De Levie

      More Details Abstract Fulltext PDF

      The spectrometric analysis of a mixture of two chemically and spectroscopically similar compounds is illustrated for the simultaneous spectrometric determination of caffeine and theobromine, the primary stimulants in coffee and tea, based on their ultraviolet absorbances. Their analysis indicates that such measurements may need an unexpectedly high precision to yield accurate answers, because of an artifact of inverse cancellation, in which a small noise or drift signal is misinterpreted in terms of a concentration difference. The computed sum of the concentrations is not affected.

    • An improved numerical approximation for the first derivative

      Robert De Levie

      More Details Abstract Fulltext PDF

      The traditional numerical computation of the first derivative $f'(x)$ of a given function $f(x)$ of a single argument 𝑥 by central differencing is known to involve aspects of both accuracy and precision. By analysing both we arrive at an algorithm that closely approximates the most accurate answer obtainable by this method, typically with at least 9 accurate decimals, while preserving a minimal footprint. The results apply to software based on the IEEE-754 specification, and are illustrated with Excel.

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