NATURE

Ultraviolet



Ultraviolet

Spectroscopy Visible and Ultraviolet

Visible Spectroscopy

Visible spectroscopy is one of the techniques more widely and more frequently used in chemical analysis. For a substance to be active in the visible should be colorful: a substance which is colored, it is because it absorbs certain frequencies or wavelengths visible spectrum and transmits others. For example, a solution is yellow because within the visible region absorbs radiation in the range from 435 to 480 nm. In this range Wavelength is the blue color of the visible, so that this compound absorbs blue and transmits the complementary colors that give rise to color yellowing of the above solution. The absorption and transmission of wavelengths in the visible region of this part of spectrum is not the same in substance that give different shades of yellow, so we can have a different range of colors like canary yellow, yellow lemon, pale yellow, and so on (www.chemistry.about.com). Table I gives a ratio range of wavelengths absorbed by the compound, color and observed color absorbed or transmitted.

The vacuum ultraviolet is considered that the region between 100 and 190 nm. It is so called because the nitrogen atmosphere absorbs this type of radiation, so the gap should be performed to exclude the absorbance of this gas absorbance's of the compound under study. Technical complications associated with the vacuum required in addition to the limited use you have in the vacuum ultraviolet, this technique has made virtually no use and in fact has no equipment commercially available for applications this type of spectroscopy. The visible and ultraviolet spectrum, however, has wide application and are techniques that are used continuously. The visible range is considered the 380 to 750 nm. The near ultraviolet range or Quartz is from 190 to 380 nm. The basis of visible and ultraviolet spectroscopy is to measure the intensity of color (or absorbed UV radiation) at a specific wavelength compared with other solutions of known concentration (standard solutions) containing the absorbing species. To have this relationship is used Beer's Law, which states that for a single absorbing species in a cell of constant thickness, the absorbance is directly proportional to concentration (www2.chemistry.msu.edu).

Table 1: Different regions of the spectrum and their ultraviolet and visible ranges or areas understood.

More often, leads to the formation of a colored complex that absorbs in the visible, and that is specific to the element or compound to be quantified calorimetrically. Example: the formation of a colored complex when free chlorine reacts with ortotoluidina, or quantification of glucose in the blood and urine by the action of molybdate under certain conditions, or rising color of copper ion, forming an ammonia-copper complex, which is formed when aqueous solution containing copper ions is added to ammonium hydroxide.

This requires a control of certain conditions that inhibit or promote the formation of colored compounds:

1. PH: pH is a determining factor in the formation of certain complex or compound colorful. When the pH influences the analytical technique, it requires proper ...