Chemists and biochemists use this technique routinely.  Also, crossed
polarization of transmitted light.

At 10:03 AM 3/9/2000 -0400, you wrote:
>Yes, for years  oceanographers have been using refractometers to
>measure salinity of seawater; e.g. oceanic water at salinity 30 ppm has
>the refractive index of 1.025 (distilled water RI=1.000). I have never
>measured buffers, but if you could  get hold of a refractometer, you can
>do a measurement  in a second.

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*  Michael Cammer * Analytical Imaging Facility * Albert Einstein   *
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