A computer-controlled all-tantalum stopped-flow microcalorimeter with microjoule resolution

Abstract A new all-tantalum differential stopped-flow heat-conduction microcalorimeter with microjoule resolution has been developed. The instrument consists of two matched channels, each of which has two reagent inlet lines. A computer is used to process the data and control the syringe drive system which runs the samples through the calorimeter. The reagents are mixed in 0.6 s in ratios of 1:1, 1:2, 1:2.5, 1:4, 1:5, or 1:10. The priming volume from the loading port to the mixer is 1 ml and the reaction volume of the detection tube is 160 μl. The instrument has a sensitivity of 1.60 J/V·s and a differential baseline stability of 100 nJ/s (p-p) over a 4 h period. The sample size can be reduced to 27 μl with only a 12% loss in sensitivity. With an electrical step power input, the 10–90% response is 40 s. By using a data decomposition scheme, the response time can be improved to 1 s which allows the direct measurement of moderately fast reaction kinetics. With water/water mixes, differential heats of mixing are typically (±) 2 μ J with a standard deviation of (±) 2.5 μ J. Reaction heats in the 20–50 μJ range can be measured with a standard deviation of (±) 3 μ J. A fast reaction, e.g. HCl dilution, can be completed in 150 s. When loading and priming times are included, 25 reactions can be completed in 120 min. A chilled water jacket is used to allow operation over a temperature range of 4°C to 50°C.