There are many kinds of spectrophotometers, but they are no more than three types: simple type, medium-grade type and high-grade type.
When we buy spectrophotometers, we need to consider the following aspects:
1. Wavelength detection range, wavelength selection method: the higher the range of wavelength detection of high-grade instruments, the wider the range of wavelength detection, of course, the higher the price, users need to choose the appropriate wavelength range according to their own needs; For simple instruments, the wavelength selection method is usually manual search, which has poor repeatability. The wavelength of high-grade instruments can be automatically searched or scanned according to the set mode, and the speed of high-grade wavelength scanning will also increase.
2. Beams: Beams can be divided into single-beam type, double-beam type or quasi-double-beam type. Single beam is generally suitable for measuring absorbance at a given wavelength. It can not be used for full-band spectral scanning, and requires high stability of light source and detector. Dual beams can be automatically recorded and scanned in full band, which can eliminate the influence of instability of light source and sensitivity change of detector, and is especially suitable for structural analysis. False double beams, also called proportional double beams, have the advantage of being able to monitor the errors caused by the change of light source. Its principle is that the light emitted by the same monochromator is divided into two beams, one directly reaching the detector, and the other reaching the detector after passing through the sample. But this method can not eliminate the influence of reference.
3. Light source: Tungsten lamp and tungsten halide (320-2500 nm) are the main light sources in visible region. In the ultraviolet region, hydrogen lamp and deuterium lamp (180-375 nm) are used. Xenon lamp can be used as light source in both ultraviolet and visible regions.
4. Sample holder: Simple sample holder is push-pull quadruple pool holder, which can only measure one sample at a time, and the reference and sample can be measured twice. The high-grade sample pool bracket has two fixed types, namely, sample channel and reference channel, which can simultaneously measure the reference value and the absorbance value of the sample.