Stopped-flow attachment for CD spectropolarimeters

Before going ahead with the purchase of an attachment for a wavelength scanning instrument, it is advisable to check that the electronic response of your instrument is fast enough for millisecond time constant acquisition of kinetic data—the Jasco J-720, for example, needs a minor modification to remove a 

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An alternative stopped-flow attachment, designed for use with Jasco J-700 series spectropolarimeters, is the HI-TECH Scientific SHU-61CD with pneumatic drive. Its temperature range is 5-80 C, its pathlength is 2 mm, it has a 3.5 mm window size and a cell volume of 19 (i,l. The mixer is integral to the cell. 200 p,l is required per shot with 2 ml to prime the flowlines. Drive syringes may be altered to allow variable mixing. Hi-Tech do not offer a dedicated stopped-flow circular dichroism system. 

Although this combination will perform adequately where CD changes are of good intensity, one should be cautious if the need is to measure fast reactions accompanied by small changes in CD. 

Ratio mixing thus requires selection of appropriately sized drive syringes. The viewport on the CD stopped-flow cell has the dimensions 10 x 3 x 2 mm (i.e. 60 pi). The dead time for the instrument varies according to the drive ratio (about 4 ms for a 1 1 mix and 8 ms for a 1 10 mix). For a research group already using an SX.18MV spectrometer, the CD.2C provides a convenient upgrade path for the measurement of CD kinetics. 

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