Rapid and precise temperature control of samples flowing through a capillary from −20 to 130 °C

The focus of this paper is on the development of an apparatus capable of rapid and precise temperature control of liquid samples circulated through a small-bore glass capillary over a range from -20 to 130 °C, with stability better than 10 mK rms. Temperature regulation is achieved by lowering the capillary into a dry gas stream that flows through a narrow slit in a wide aluminum nozzle whose temperature is controlled by two thermoelectric modules (TEMs) that transfer heat between the nozzle and coolant flowing through a heatsink. Rapid thermal equilibration between the capillary and nozzle occurs primarily through conductive heat exchange with the flowing gas. The performance of the temperature controller is well described by a heat-transfer model, with low heat-capacity components enabling fast temperature slew rates. The temperature-control head is compact and can be fitted with customizable apertures suitable for visual access to the capillary and for transmitting focused electromagnetic radiation through it. However, the thermal cycling of the TEMs at high operating temperatures led to the rapid degradation of their cooling capacity. To mitigate this issue, separate low-(∼4 °C), room-, and high-temperature (∼85 °C) coolant reservoirs and pinch valves were used to select the coolant reservoir based on the target temperature, thereby limiting the maximum temperature experienced across the TEMs during thermal cycling and dramatically extending their operational lifetime. This apparatus was designed primarily for temperature-dependent, time-resolved x-ray scattering studies of biomolecules in solution but has also been used in time-resolved spectroscopic investigations.