Take Home Point:

Low and major level elemental analysis of 'dirty' liquid and solid samples and unknowns  

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What It Provides:

Provides concentration tables of low and major level components and impurities present in 'dirty' liquid and solid samples (after digestion) as well as unknowns.

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Brief Description

 

Sample into Plasma/UV and Visible Light Out

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In ICP-OES (also called ICP-AES) samples are first subjected to an inductively coupled plasma (ICP).  The plasma produces excited atoms and ions which emit UV and Visible light with wavelengths that are characteristic of individual elements present in the sample matrix.  An Optical Emission Spectrometer (OES) detects the emission wavelengths and quantifies the elements present.    

 

Samples must be in liquid form for analysis.  Sample preparation typically involves digestion with acidic solutions and sometimes heat.  Microwave digestion is also used.  The samples are then reconstituted in a slightly acidic aqueous matrix for analysis.  Liquids can be analyzed directly or after dilution assuming that the total dissolved solid levels is <~0.5%.

 

The prepared liquids are then introduced into the instrument using a nebulizer that converts it into a fine mist.  The mist is then carried into a spray chamber with a stream of gas to remove large droplets.  The mist then enters a 'torch' which mixes the sample with additional gas flow before exposing it to the plasma (typically Ar).  Within the plasma the sample separates into individual atoms due to the extremely high temps and some of the atoms are subsequently ionized.  Some of the atoms and ions are then excited to higher energy levels.  As they relax back to their ground states they release energy equal to the energy difference between the excited and ground states.  These energy differences are unique for each element.  A photometer is used to measure the wavelengths (which is inversely proportional to the energy) of the emitted light to determine the elements present and their amount.     

 

ICP-OES is similar to ICP-MS except that in the latter detection is based on measuring the mass of the ions formed within the plasma.  ICP-MS is more sensitive and has less interferences while ICP-OES is more robust.   ICP-OES is better for 'dirty' samples with high levels of suspended and/or dissolved solids where ICP-MS samples should be relatively clean.  ICP-OES is good for unknowns as well.