Improved magnetic suspension densimeter for biochemical reactions

An improved version of our magnetic suspension densimeter has been developed for use with samples of aqueous systems as small as 100 μl. The instrument’s sensitivity to a change in density of the solution under test (measured as a voltage shift) is 0.1 mV≊4.5×10− 6 g ml− 1, with a base‐line drift less than 9 μV/h. The nonlinearity of the densimeter’s response is less than 5 ppm over its calibration range. In this paper, we describe the new magnetic suspension circuit, discuss the precision limits of the instrument, and present the results of measurements made on a tetracarboxylate sequestering agent known as BAPTA which we use as a calcium‐ion indicator.