![]() ![]() This process is referred to as sputtering. If the kinetic energy of the noble gas cations is high enough, some of the metal atoms on the cathode will be dislodged, producing an atomic cloud of metal in the gaseous phase. These charged noble gas atoms collide with the cathode. ![]() As the electrons migrate toward the cathode, they collide with the noble gas atoms and ionize them. Lamps containing more than one element in their cathode are also available but most FAAS and FAES instruments can only measure one element at a time.Ī HCL works by placing a 300 V potential across the electrodes that generates a current of 5 to 15 milliamps (mA). HCLs also contain a tungsten anode, a cathode composed of the metal of interest, and various insulators (usually made out of mica). These cylinders are filled with a noble gas (Ne or Ar) to sub-atmospheric pressures of 1 to 5 torr. Glass end caps can be used for visible wavelength emitting materials while quartz must be used for UV emitting HCLs. These lamps are encased in a cylinder made out of glass walls and a quartz end cap. A schematic of a Calcium HCL is shown in Animation 2.1 below. The most common line source radiation generator used in AAS is the hollow cathode lamp (HCL). Line sources are lamps that emit very narrow bands of radiation, but this source of radiation is not as pure as radiation from a laser. These various lamps are used as background correction lamps (signal to noise correction devices) in AAS and AES instruments and not as source lamps for analyte detection. Examples of lamps considered to be continuous sources are deuterium, mercury, xenon, and tungsten lamps. The emission wavelengths of a continuous source can range over hundreds of nanometers. A plot of intensity on the y axis and wavelength on the x axis is shaped like a broad Gaussian distribution with a few small peaks and shallow valleys. ![]() A continuous source, also referred to as a broadband source, emits radiation containing a broad range of wavelengths. There are three basic types of radiation sources that are utilized in these instruments: continuous sources, line sources, and laser sources. 2.2 Components of a Flame Atomic Absorption/Emission Spectrometer Systemįor FAAS and FAES, the wavelengths of interest are in the UV and visible range. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |