When we buy spectrophotometers, we need to consider the following aspects:
5. Slit: Simple slit is generally fixed width mode, slit width is mostly 2 nm, but also 1.5 nm; The slits of high-grade instruments are continuously adjustable, which can meet the needs of high resolution.
6. Optical performance indicators: The optical performance directly affects the accuracy of measurement, especially the grating technical indicators. The grating quality of high-grade instruments is better, and the best grating is concave. And the larger the number of grooves corresponding to the large-size concave grating, the better the resolution and stray light indicators than the simple instrument.
7. Detector: Detector is a device that uses photoelectric effect to convert the optical signal through solution into electrical signal and amplify the electrical signal. Simple instruments generally use photosensitive diodes; medium-grade instruments use silicon photodiodes; The detectors of high-grade instruments use photomultiplier tubes with high sensitivity and infrared detectors.
8. Display: Most of the simple instruments are mechanical head or digital tube display, without data processor. The display of high-grade instrument is liquid crystal or connected to computer. Data processing can be processed by the instrument itself or by external computer.
9. Measuring mode: Simple instruments are mostly fixed-point (fixed wavelength) absorbance or transmittance measurement methods, and can hardly carry out wavelength scanning measurement. There are many measuring modes for high-grade instruments, which can display transmittance, absorbance, concentration direct reading, single beam, single point and scanning.
10. Measurement accessories: The important aspect of measuring the quality of the instrument is to see whether the instrument has abundant accessory measuring devices, such as polarization accessories, integrating sphere accessories, reflection accessories, automatic sampler accessories, color analysis software and film accessories.
11. Measure the state of the sample: Visible and ultraviolet spectrophotometers generally measure liquid samples. Infrared spectrophotometers can generally analyze samples in various states (gas, liquid and solid).