spectrometers :• Spectrometers are instruments used to identify, measure,and analyze specific wavelengths of substances along aspectrum that is, a group of related data.• It breaks light into a spectrum, which is the lights collectionof component colors, all of which make up the color of thelight as a whole.• These spectra are different for every element.• This means that by recording the spectra of differentelements, one can obtain a reliable method for identifyingelements based on the spectra observed. If a certainspectrum is similar to the spectrum of a known element, it canbe said that the observed element is that known element.
History of spectrometer :• The invention of spectrometers and the science ofspectroscopy go back to very ancient times. Each inventionadded more knowledge about the nature of light and mass andits interaction.• Sir Isaac Newton invented a simple spectrometer when heused a prism to disperse white light into its constituent colorsin the late 1600s.• In 1801 British scientist William Wollaston investigated thedark lines in the solar spectrum that suggested the absence ofcertain spectra of light.• German physicist Gustav Kirchhoff was able to show thatpurified substances display unique light spectra in 1859.
• Further work by Johann Balmer, Johannes Rydberg, andNiels Bohr was able to detect the energy levels of hydrogenaccurately. But it was the work of Werner Heisenberg andErwin Schrodinger in 1925 that helped to explain the spectraof most elements.
Essential components of a spectrometerSlitCollimatorPrism or gratingTurntableVernier scaleTelescope
Slits• Slits is a narrow opening through which light entersCollimator• It consist of a fixed metallic tube with convex lens at oneend and an adjustable slit on other end. When slit is just atthe focus of the convex lens the rays of light coming out ofthe lens become parallel. For this reason it is called collimator.Diffraction Grating• It is a glass plate having a large number of close parallelequidistant slits mechanically ruled on it.Prism• A prism is a transparent optical element with flat, polishedsurfaces that refract light. At least two of the flat surfacesmust have an angle between them.
Turntable• A Prism or a grating is placed on a turntable which is capableof rotating about a fixed vertical axisVernier scale• It is a circular scale graduated in half degrees is attachedwith turn tableTelescope• It is attached with a vernier scale and is rotatable about thesame vertical axis as the turntable
Prism spectrometerAn instrument composed of a collimator, a prism table, and atelescope is called a prism spectrometer.
Operation•Light enters through aslit at one end of thecollimator and emergesparallel to the axis of thecollimator at the other •The prismend. The collimated light deviates and disperses thethen strikes a prism that collimated light according tohas been appropriately Snell’s law and thepositioned on the different wavelengths of lightspectrometer table. present in the light source. The sets of parallel rays (one set for each wavelength) then enter the telescope and form separate, distinct images of the collimator slit when viewed through the telescope.
Grating SpectrometerA grating spectrometer is in every way similar to a prismspectrometer with the exception that a simple, planediffraction grating replaces the prism as the dispersingelement. The function of the collimator and telescope, as wellas the general operation of the spectrometer remainsunchanged.
More Kinds of spectrometer :There are many types of spectrometers, with many possiblevariations and modifications that can specialize or extend theusefulness of an instrument.Reflection SpectrometersReflection spectrometers are used to measure the specificwavelengths of light that are reflected by a substance. Thisis similar to the basis of human vision, which identifiescolors using the wavelengths of reflected light.Acoustic SpectrometersAcoustic spectrometers use sound instead of light. They applypulses of sound to a material and measure how much ofparticular frequencies of sound pass through the material andhow fast different frequencies of sound pass through thematerial.
UV SpectrometersUltraviolet (UV) spectroscopy works on a principle similar tothat of colorimetry , except the light applied to the sample isin the ultraviolet range. UV spectroscopy is also calledelectronic spectroscopy, because the absorbancecharacteristics of a sample depends on the configuration ofelectrons in the chemical bonds of the sample compound.IR SpectrometersInfrared (IR) spectrometers measure the response of asample when exposed to infrared light. A range of IRwavelengths are passed through the sample to record theabsorbance. IR spectroscopy is also called vibrational orrotational spectroscopy because the vibrational and rotationalfrequencies of atoms bonded to each other, are the same asthe frequencies of IR radiation.
Atomic SpectrometerAtomic spectrometers are used to analyze the elementalcomposition of samples and to determine the concentrations ofelements of interest. There are two basic types of atomicspectrometers---emission and absorbance. The wavelengths ofthe emissions or absorbances are characteristic of theelements present.Emission SpectrometersEmission spectrometers work on the principle that when achemical element is heated by a flame or electric arc it willemit energy. This energy is in the form of light. Thespectrometer separates the light into individual frequencies.Because of the quantum nature of light and matter particularelements will only emit light at specific frequencies.Therefore, analysis of the output of a spectrometer allows youto identify particular elements.
Absorption SpectrometersAbsorption spectrometers are basically the exact opposite ofemission spectrometers. Just as heated elements only emitlight at specific frequencies, they only absorb light at specificfrequencies. Absorption spectrometers work by shining lighton a sample of a substance and noting which frequencies areabsorbed.
Uses•Spectrometers are used extensively inastronomy, archaeology and chemical analysis.• With the help of prism spectrometer the deviation of lightby a glass prism and refractive index can be determined• Using diffraction grating the spectrometer can be employedto measure the wavelength of light• UV spectrometers are used to study chemical bonding and todetermine the concentrations of substances (nucleic acids forexample) that do not interact with visible light.• . IR spectrometers are used to identify unknown compoundsor to confirm their identity since the IR spectrum of asubstance is essentially unique.• Absorption spectrometers are used in astronomy todetermine the atmospheres of distant planets. They are alsoused in chemistry to find out what elements are present inchemical samples.
• Acoustic Spectrometers provides information about thevarious physical properties of the material. If the material ismade up of different particles (e.g. sand) acousticspectrometers can tell you how large the sand grains are.
Fields That Use Spectrometers• Chemists were the most frequent users of spectrometersand their data, but as refinements and innovations inspectrometers came about, broader uses for the equipmentwere developed. Today, spectrometers are used to analyzespecific types of data in the fields of physics, astronomy,engineering, pharmacology, manufacturing, and medicine.
New Uses for Spectrometers• Scientists are continually finding new uses for spectroscopydevices to improve our world. Most recent is an instrumentcalled an Inductively Coupled Plasma Mass Spectrometer (ICP-MS), which can detect minute quantities of traceelements, such as uranium in nuclear plant workers urine --thus helping to safeguard the health and well-being of theseworkers.