SX Series
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SX Series of Stopped-Flow Spectrometers SX20 | SX20-LED

TABLE OF CONTENTS Instrument Overview Capabilities and Performance Advantages Stopped-flow cell design Absorbance measurements Fluorescence measurements and inner filtering Instrument dead time Automatic measurement of dead time Chemical determination of dead time Temperature-dependent kinetics Accessory Options Sequential-Mixing Accessory 5 μL Volume Low Dead Time Cell Quench-Flow Adapter Photodiode Array Detector ProKIV Global Kinetic Analysis Software Scanning Emission Monochromator Scanning Monochromator (far-UV) and photometric accuracy Dual Fluorescence Detection Fluorescence...

INSTRUMENT OVERVIEW Applied Photophysics Ltd. is the world’s leading producer of stoppedflow spectrometers, with thousands of stopped-flow spectrometers supplied since 1991. We have manufactured kinetic instrumentation since 1971 and have pioneered the development of modern stopped-flow instrumentation. Our ongoing development of stopped-flow applications and our large customer base are your assurance that we provide world class expertise and technical support for your kinetics research with the SX20 stopped-flow spectrometer.

Ultra-stable Xenon light source suitable for all absorbance and fluorescence applications Programmable monochromator enabling acquisition of both absorbance and fluorescence kinetic traces and steady-state spectral acquisition Optimised detectors for fluorescence and absorbance kinetics with no reconfiguration required when switching between these techniques Time-dependent PDA spectra in the time range of 1 ms to 20 s Unique lower inner filtering / high-sensitivity cell designs Low dead time, low volume requirement ProData acquisition, display and analysis software (unlimited seats) Large...

High-intensity LED light source. Over 40 wavelengths available from 280 nm to 830 nm Very high fluorescence sensitivity Extremely high stability, rapid start-up and long lasting Cost effective Small footprint Unique lower inner filtering / high-sensitivity cell designs Low dead time, low volume requirement ProData acquisition, display and analysis software (unlimited seats) Large range of upgra

SX20 STOPPED-FLOW SPECTROMETER The SX20 includes everything required for highly sensitive fluorescence, light scattering and absorbance kinetics. The versatility of the SX20 makes it an ideal choice for a wide variety of stopped-flow applications, as well as instruments intended for use by several research groups. It has photomultiplier detectors optimised for both absorbance and fluorescence detection and a Xenon light source that is stable to within an absorbance of 0.001 over any time range up to 1000s. Switching between absorbance and fluorescence detection is always straightforward,...

The standard 20 μl volume cell has a dead time of 1.1 ms and optical pathlengths of 10 mm and 2 mm for absorbance, and 1.5 mm and 5.5 mm for fluorescence (the lower pathlength is particularly useful for minimising the inner filter effect without compromising sensitivity). Stopped-flow cells are rapidly interchangeable and shorter dead time cells are available. Other standard features include automatic dead time and drive volume measurement. Instruments are supplied with the powerful ProData control and analysis software and a PC running Windows 11 with USB communication to the instrument.

SX20-LED STOPPEDFLOW SYSTEM The SX20-LED stopped-flow is a recently introduced version of the SX20 that is ideally suited for applications that are likely to involve sample irradiation at just a few specific wavelengths, such as fluorescence applications. With the SX20-LED stoppedflow system, one or more LED light sources replace the standard Xenon light source and monochromator. This reduces both the instrument’s cost and bench footprint. The SX20-LED can also provide a sensitivity improvement because LEDs are highly stable and typically around ten times more intense than the corresponding...

The second data example, shown at right, shows the refolding kinetics of lysozyme recorded both with and LED and a Xenon lamp at 280nm. In this example, the signal-to-noise improvement using the UV LED is about a factor of 2. The difference in noise can be seen in the zoomed in region in the lower plot. LED light sources also have a quicker warm-up/ stabilisation time: about five minutes, compared with about 30 minutes for a Xenon lamp. The SX20-LED system also has a much reduced footprint over the standard SX20 spectrometer: 1 m of bench space is all that is required. The LED power supply...

CAPABILITIES AND PERFORMANCE ADVANTAGES Stopped-Flow Cell Design Absorbance measurements At the heart of the SX20 / SX20-LED is a removable cell cartridge housing the stopped-flow cell. The standard 20 μL volume quartz cell has dimensions 10 mm x 2 mm x 1 mm, and provides optical pathlengths of 10 mm and 2 mm. To switch optical pathlengths, the user simply relocates the detector and light guide – a task that takes about one minute to complete.

Fluorescence measurements and inner filtering The stopped-flow cell is uniquely optimised for fluorescence detection because the ‘fifth’ side of the cell is dedicated to this purpose. This means The cell is able to incorporate a light pipe specifically designed to maximise collection of fluorescence emission. The inner filtering effect (see below) can be low without having to compromise sensitivity by reducing the cell volume. No reconfiguration is required when switching between absorbance and fluorescence detection. The inner filter effect is caused by reabsorption of light emitted by the...

Instrument Dead Time The instrument dead time can be defined as the earliest time at which valid measurements of the reaction can be made. A short dead time is required for measurement of very fast reactions. A sub-millisecond dead time is relatively easy to achieve by simply using a very small volume stopped-flow cell; however, a small cell also has more limited practical use because For absorbance measurements, only a small optical pathlength is available, producing only a small change in signal. For fluorescence measurements, only a small volume of sample can be excited, resulting in low...