Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES)
ICP-OES began in 1964. Many advances have been made since the first commercial instruments were first introduced to the analytical field. As with most new techniques, the original optical emission results using ICP sources were not spectacular. The technique continued to be refined as sources of background “noise” were determined and eliminated, and gas flows, torch designs, and plasma settings were optimized. By 1973, the low detection limits, freedom from inferences, and long linear working ranges obtained with the ICP proved that it was clearly an emission source superior to those used previously in analytical optical emission spectrometry. Since that time, an increasing number of academic, governmental, and industrial researchers have joined in the development of the ICP.
Summary of Method
An ICP source consists of a flowing stream of argon gas ionized by an applied radio frequency field. This field is inductively coupled to the ionized gas by a water-cooled coil surrounding a torch that supports the plasma. A sample aerosol is generated in an appropriate nebulizer and is carried into the plasma through an injector located within the torch. The sample is injected directly into the ICP, subjecting the constituent atoms to temperatures of about 6000-8000 Kelvin (10,340-13, 940 Fahrenheit). Because this results in almost complete dissociation of molecules, significant reduction in chemical inferences is achieved. The high temperature of the plasma excites atomic emission. Ionization of a high percentage of atoms produces ionic emission spectra. The light emitted by the ICP is focused onto the entrance slit of a monochromator that effects dispersion. An exit slit is used to isolate a portion of the emission spectrum for intensity measurement using a photomultiplier tube. The light emitted by the atoms or ions in the ICP is converted to electrical signals by the photomultiplier in the spectrometer. The intensity of the electron signal is compared to previous intensities of known concentration of the element, and a concentration is computed for reporting purposes.
Our division currently operates an ICP-OES model Optima 3300, manufactured by Perkin-Elmer Corporation. This unit is used detect trace metals in various media.
Gas Chromatography and Gas Chromatography/Mass Spectroscopy (GC-MS)
These are used to detect and quantitate specific organic contaminants. GC analysis separates all of the components in a sample and provides spectral output. The sample is injected onto the injection port of the GC. The instrument vaporizes the sample and then separates and analyzes the various components. Our lab uses the Flame-Ionization Detector Gas Chromatograph (FID-GC) to detect oil or solvents from spills and illegal dumping. The Electron Capture Detector Gas Chromatograph (ECD-GC) is used to identify polychlorinated biphenyls (PCBs) in media. GC/MS combines the separating power of gas chromatography with the sensitivity and specific characterization of mass spectroscopy. After a sample is introduced and volatilized, the individual components of a mixture are separated on a GC column and then characterized using a mass selective detector. In many cases the components can be directly identified from their mass spectra using the library database.
Our lab uses a purge and trap along with the gas chromatograph and mass spectrometer for analyzing volatile organic samples. This devise purges volatile materials from a water sample by bubbling an inert gas through the sample, and then traps the volatiles on a charcoal filter for further analysis.
Fourier Transform Infrared Spectrometer (FT-IR)
This instrument is used to identify unknown solids and liquids. Infrared spectrometry is a technique that involves exposing samples to various wavelengths of light and observing the response. Molecular bonds bend and stretch in different ways depending on the structure of the molecule and the functional groups attached. Individual compounds produce unique spectra that can be used to identify the substance. FT-IR is an advanced infrared spectrometry technique that allows the spectrometer to see all of the wavelengths at all times, improving both speed and resolution.
Ion Chromatography
This instrument allows for simultaneous analyses of multiple ion parameters on a single sample. Through ion exchange, the various ions are identified by their respective retention times and concentrations are determined by conductivity. Although conventional colorimetric and trimetric methods were used for determining individual ions, only ion chromatography provides a single instrumental technique that can be used for rapid, sequential measurement. In addition, ion chromatography eliminates the need to use hazardous reagents, and effectively distinguishes among halides and oxyions.
General Tests
There are a number of general tests used to analyze the chemical and biological components of wastewater, storm water, and surface water. These tests provide us with information on what is going into our waterways and our water treatment plant. These general analyses can also give us an indication of any illegal discharging into waterways and public owned treatment works. Typical tests performed in our labs are pH, conductivity, dissolved oxygen, biological oxygen demand, chemical oxygen demand, fluoride, turbidity, solids, ammonia, nitrite, cyanide, phenol, phosphorus, oil and grease, total petroleum hydrocarbons, detergents, and harness.