The popular understanding is:
Single-channel scan: high sensitivity and high resolution, but the large size of the instrument, the test speed is slightly slower than the full spectrum.
Full spectrum direct reading: The test speed is slightly faster (on average, a sample is 1 to 2 minutes faster than a single scan), the stability is relatively good, and the instrument is small in size and compact.
There are two main components that cause the difference between the two detection methods, that is, the detector used by the instrument, namely CCD and PMT.
Photomultiplier tube referred to as PMT
1. Both PMT and CCD are detectors of spectrometer. PMT uses a high voltage of 1000V as the working voltage, while CCD uses a low voltage of 42V as the working voltage. When detecting high-purity substances, such as 99.997% electrolytic aluminum or electrolytic copper, the advantage of PMT is obvious. CCD detectors cannot detect such high-purity substances. But in the analysis of various alloys, the two detectors are basically the same.
2. Because the CCD detector uses the full spectrum technology, it can receive all the spectral lines, so it can achieve real-time peak correction, eliminating the need for peak correction work for PMT spectrometers, and greatly improving work efficiency. In fact, the CCD spectrometer automatically completes the peak correction work in the first second of exciting the sample.
3. PMT currently has the best single-wavelength detection performance, which includes sensitivity and stability, signal-to-noise ratio and many other aspects. The photomultiplier tube is divided into different wavelength ranges, different light intensity ranges, and different application conditions. It is not known how many types are divided, but for the spectral range of the direct reading spectrum, application conditions, according to the light intensity range conditions and wavelength sensitivity. There is the kind of tube that is most suitable for it. Even if it is a model of tube, the white light sensitivity of each tube will be marked when purchasing. This is also very different for each tube.
4. The CCD collector is just a solid imaging system that collects the entire band under one condition. How can it be possible to average the collection efficiency or keep the best? There are also many types of CCDs, but in order to reduce costs, it is basically impossible to configure more than two (blocks) of CCD collectors in one instrument, because in this case, its cost advantage is gone, and there are many more Other incidental issues. In addition, the slow response time of illumination is also a flaw of the CCD collector, which will make many advanced data time filtering techniques not applicable (nS level). Here, a comparison of the collection effect of a single arbitrary wavelength is made.
Then let's talk about the overall acquisition effect. The biggest advantage of the CCD collector is that it can scan the full spectrum, which is convenient and comprehensive, and it can be small in size with the echelle optical system.
In short, PMT and CCD have their own advantages and disadvantages in the field of inductively coupled plasma emission spectrometer. The advantages of PMT
＆#8226; PMT has a wider dynamic range. The dynamic range of PMT is 106, while that of CCD is 104. The signal-to-noise ratio of CCD is not as good as PMT.
#8226; The extremely low detection limit of PMT for certain elements is now unreachable by CCD.
PMT is an old technology for nearly 30 years, and everyone has become accustomed to its operation. PMT technology is commonly used in domestic inductively coupled plasma emission spectrometers.
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