Main Technical Indicators of Ultraviolet-Visible Spectrophotometer

Release time：2019-03-19

The common main parameters of ultraviolet-visible spectrophotometer and other instruments are as follows:




1. Optical system: generally refers to the structure of optical system. At present, self-collimation and CT are commonly used in domestic and international photometer industry.



2. Wavelength range: refers to the difference between the maximum and minimum wavelength that a photometer can test.



3. Wavelength Accuracy: The instrument shows the proximity between the wavelength and the real wavelength, that is, the difference between the set wavelength and the actual wavelength. Each photometer checks wavelength accuracy at many wavelength points.



4. Wavelength repeatability: Wavelength repeatability is the ability of the instrument to return to its original wavelength. It embodies the stability of the wavelength-driven machinery and the whole instrument.



5. Spectral bandwidth (sensitivity, resolution): refers to the half-width of energy detected on a detector when a peak spectral band passes through a slit of a monochromator. It is more easy to understand this concept from another point of view by using wavelength unit nm. Firstly, the slit of a monochrome not only represents the physical or geometric size of the slit, but also represents the optical meaning. It is the spectral bandwidth. We know that the light from the monochromator is not only a single wavelength light, but a narrow spectral band arranged in order of the size of the wavelength. This spectral band contains the number of wavelengths, which is expressed by the spectral bandwidth. Spectral bandwidth directly reflects the degree of monochromaticity of light coming from the monochromator. This index is similar to the resolution and sensitivity of the instrument, but different from each other. They reflect the performance of the photometer from different sides. Resolution refers to the ability of the instrument to distinguish two adjacent wavelengths. If two pulses are input to the input of the instrument at the adjacent two wavelengths and the analog signal detected on the detector of the instrument is less than 80% of the maximum value, the two wavelengths are considered to be distinguishable according to Rayleigh criterion. Benzene vapor is usually used to measure the actual measurement (the peak and valley between 258.9 and 259.3 nm). Sensitivity refers to the change of signal on the detector when the concentration changes one unit in the measurement of low concentration. It is limited by the calibration curve (the concentration of standard curve is horizontal axis, the absorbance is vertical axis) and the precision of the instrument itself. When the precision of the two methods is the same, the greater the slope of the correction curve, the more sensitive it is. When the slope is equal, the higher the precision, the better the sensitivity. It should be pointed out that in order to obtain accurate test results, the ratio of the spectral bandwidth (SBW) of the instrument to the natural bandwidth (NBW) of the analytical sample should be less than 0.1, so that more than 99.5% of the measurement accuracy can be obtained.



6. Stray light: Stray light is a signal produced by non-selective wavelength light irradiating on the detector, and it is an important source of photometer analysis error. Stray light will limit the accuracy of high concentration solution analysis. Stray light is expressed by T%.



7. Spectrophotometric range: refers to the test range of the photometer under various technical indicators, expressed in A or T;



8. Photometric accuracy: refers to the degree to which the average values measured repeatedly correspond to the true values;



9. Photometric precision: refers to the degree of coincidence between parallel measurements under the same conditions.



10. Baseline flatness: refers to the distribution of instrument noise in the full wavelength range;



11. Drift: The degree to which the instrument deviates from the initial value over time. It depends on the stability of light source and electrical device. For a single beam instrument, the preheating time has a great influence on the drift.



12. Noise: refers to the sum of non-useful signals detected by the instrument, which is relative to the signal. Generally, there are two sources of noise in spectrophotometer, one is from the light source, the other is from the inherent electronic noise inside the instrument, such as power supply, amplifier, AD converter, etc. In order to reduce noise and improve signal-to-noise ratio, it is necessary to have a good electrical design. Noise affects the repeatability and accuracy of measurement at low concentration. Noise can be partially eliminated by taking the average value after repeated measurements.