Evaporative Light Detector / UV Detector / Chromatographic Detector
1 function
The concentration of the analyte group in the column effluent is converted into an optical or electrical signal;
2 UV detector
The working principle of the instrument is based on the law of light absorption. Light from the light source through the slit, filter, sample cell to the optoelectronic tube, the beam due to different sample concentrations caused by changes in light intensity into a photocurrent change, the photocurrent through the amplifier input to the logarithm Converter, the light transmittance T into A output, that is, A = 1g - = εCL Where ε is the sample extinction system, C is the sample concentration, the use of molecules / liter unit, L is the optical path, Made in centimeters. According to the above formula to know the A, I know the sample concentration C. If the direct input from the amplifier recorder, plotted is the change of the sample transmittance T chart, if the input from the log converter plotted is the sample optical density A changes in the map.
Advantages: UV absorbance detector not only high sensitivity, low noise, wide linear range, better selectivity, but also less sensitive to changes in ambient temperature, mobile phase composition and flow rate fluctuations, so it can be used for isocratic elution as well Can be used for gradient elution. UV detector is not sensitive to the flow rate and temperature, in the preparation of chromatography. Because of the high sensitivity, even those with low light absorption, low extinction coefficient of the material can also use UV detector microanalysis. The company is located in:
Disadvantages: the downside is that the poor sensitivity to low UV absorption of compounds such as hydrocarbons without unsaturated bonds.
3 Photodiode Array Detector (PAD or DAD)
Ordinary UV-Vis detector can only be measured at a wavelength absorbance and time curve, that can only make two-dimensional map. To determine a component of the UV-visible absorption spectrum, the need to use the "stay scan" method, PAD can simultaneously determine the absorbance, time, wavelength of the relationship between the three through computer processing can be obtained three-dimensional map, but also to make any wavelength Absorbance-time curve (chromatogram) and absorbance at any time-wavelength curve (UV-Vis spectroscopy). An important use of PAD is the peak purity test.
4 Refractive Index Detector (RID)
RID, also known as photorefractive detector, is a universal detector. The solute concentration was determined based on the continuous determination of the change in the refractive index of the column effluent. The refractive index of the solution is the sum of the refractive index of the solvent (mobile phase) and solute multiplied by the concentration of the substance. The difference in refractive index between the mobile phase and the mobile phase themselves, concentration. In principle, any sample with a difference in refractive index from the mobile phase can be used to determine it. The detection limit of up to 10-6 - 10-7g / mL, generally can not be used for gradient analysis.
5 evaporative light scattering detector (ELSD)
ELSD is a mass-based detector that can be used to detect any non-volatile compounds, including amino acids, fatty acids, sugars, surfactants, etc., especially for difficult samples such as phospholipids, saponins, alkaloids, Steroids and other non-UV absorption or UV absorption of the compounds more than other HPLC detector incomparable superiority. In addition, ELSD is insensitive to the mobile phase composition and can be used for gradient elution. ELSD detection sensitivity is higher than the low-wavelength UV detector and refractive index detector, the detection limit can be as low as 10-10g.
6 Fluorescence Detector (FLD)
Many compounds, especially aromatic compounds, biochemical substances, such as organic amines, vitamins, hormones, enzymes and other ultraviolet light is absorbed, can absorb a certain wavelength of light, so that some of the atoms from the ground state of the lowest vibration The energy levels transition to some vibrational levels of the higher electron energy states, which then decrease to the lowest vibrational level of the first electronically excited state due to the collision of the electrons in the molecule, dissipating a certain amount of energy, and then transition back to the ground state Some of the different vibrational levels, while emitting lower than the original absorbed light frequency, longer wavelength light, that is, fluorescence. The light absorbed by these substances is called excitation light (λex) and the resulting fluorescence is called emitted light (λem). Fluorescence intensity and incident light intensity, quantum efficiency, sample concentration is proportional to. The biggest advantage of FLD is the high sensitivity and good selectivity. In general, it is 10-1000 times more sensitive than UV absorbance detectors, up to mg / L, and requires few samples for its wide range of uses in pharmaceutical and biochemical assays.
7 Conductivity detector (CD)
CD is the most widely used detector in ion chromatography. The principle is to measure the conductance of ionic solutes in aqueous solution using two counter electrodes. The concentration of solute in the eluent is determined from the change in conductance. The dead volume of this detector is small, such as the inhibition of conductivity method, the sensitivity of up to 10-8 g / mL, the linear dynamic range of 103.
8 amp detector (AD)
AD uses a solid working electrode, the electrode can be used for high positive potential, it can detect redox substances, a wide range of applications. AD structure is simple, small pool size, fast response, low noise, high sensitivity. However, due to the electrode surface is easily contaminated, the need for frequent polishing updates. AD has a DC, pulse and integral points, but also one of the commonly used ion chromatography detector.
9 Mass Spectrometry Detector (MSD)
Generally refers to the combination of HPLC-MS or HPLC-MS / MS, usually used as structural determination or compound identification. Has a high sensitivity and resolution. Currently popular interface is electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), and positive and negative two kinds of ion mode, a very wide range of applications. Other HPLC detectors are: (9) chemical reaction detector that is to be tested for a chemical reaction (derivative reaction, enzyme reaction, etc.) and then use a detector of high sensitivity detection. Such as amino acid analyzer, solid-phase chemical reaction detector (immobilized enzyme reactor) and so on.
10 Dielectric constant detector
Dielectric constant detector is a universal detector, low sensitivity, versatility. Its working principle is: with the mobile phase outflow component changes, the dielectric constant, capacitance also changes, so the determination of mobile phase capacitance changes, you can detect changes in components. Dielectric constant detector performance similar to RID, but its application is not as common as the latter.
11 Potentiometric detector
The potentiometric detector determines the potential of the effluent using an ion-selective electrode, the effluent composition changes, and the potential changes. Different ion-selective electrodes (eg, halide, silver, etc.) can be used to determine changes in different ion concentrations.
12 radioactive detector
A radioactive detector is a special detector that detects radioactively labeled components in the mobile phase. Its wide response range is insensitive to changes in mobile phase components that are not radioactive, and gradient elution techniques can be used efficiently.
13 photoconductive detector
Photoconductivity detector is the use of certain compounds by intense ultraviolet light caused by photoionization ionization phenomenon, the detection in the conductivity cell. This detector selectively responds to halides and many sulfur and nitrogen containing photoactive compounds. The photoconductivity detector is more sensitive to certain compounds than the UV-Vis detector, and has a linear range.
14 Infrared spectrum detector
Infrared detector can be used for selective detection of HPLC. This method is mainly used for gel chromatography and can only be used in systems where the mobile phase does not absorb infrared wavelengths used. Currently more applications are Fourier transform infrared spectroscopy detector, that is, HPLC-FTIR combined, due to the scanning speed, do not stay can get the infrared spectrum of each peak.
15 Coulometric array electrochemical detector
Coulomb array electrochemistry is a new type of detector with very high sensitivity (10-15) for three-dimensional chromatograms (time, potential, concentration) for the determination of electrochemically active substances.
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