Quantitative Chemical Analysis
Elemental Analysis, Trace Analysis & More
Quantitative chemical analysis is performed to accurately determine the concentration, amount or percentage of one or more elements in a test sample. This technique, along with qualitative analysis, provides information on what and how much of each element is present in a sample for a complete elemental analysis. Quantitative chemical analysis can determine the alloy composition of raw materials, verify conformance to a specification or help with an investigation into a manufacturing problem or product failure when evaluating foreign materials or contaminants that affect material performance.
Laboratory Testing Inc. has the capabilities to provide quantitative and, in some cases, semi-quantitative results for liquid and solid samples using a variety of elemental analysis and trace analysis methods:
- Atomic Emission Spectroscopy (AES)
- ICP-AES Analysis
- ICP-MS Analysis
- Carbon and Sulfur Determination
- Inert Gas Fusion
- Energy Dispersive X-ray Spectroscopy (EDS)
- Portable X-Ray Fluorescence Spectroscopy
- Fourier Transform Infrared Spectroscopy (FTIR)
- Gravimetric and Volumetric Wet Chemistry Analyses
- Trace Element Analysis
The best method of analysis generally depends on the type of sample, quantity of material available for analysis, desired result and cost constraints. Most of these methods provide trace analysis and can detect parts-per-million concentrations or even parts-per-trillion ranges with some of the latest spectroscopy equipment in the lab. All of the quantitative chemical analysis processes mentioned above, except for XRF spectroscopy, are considered destructive because a small specimen must be removed from the sample in order to perform the test.
Quantitative Analysis Processes
Atomic Emission Spectroscopy
Atomic Emission Spectroscopy determines major, minor and trace elements and is particularly useful for low atomic number elements such as boron, aluminum, calcium, magnesium and phosphorous. Elemental analysis by AES is a process of energizing atoms in a test sample to create emission lines or wavelength bands from emitted light. Atoms create their own unique pattern and the intensities of the emission lines increase in proportion to the number of atoms producing the lines. The analysis entails comparing the emission lines from the sample to known standards to identify the element and calculate the quantity of the element.
The specimen is prepared by grinding to obtain a uniform, clean, flat area. The atoms in the sample are energized using a rapid series of high energy sparks in an argon-filled gap between an electrode (cathode) and the surface of the specimen. When the excited atoms in the plasma relax (de-excite) to a lower energy state, they emit light at characteristic wavelengths for each element.
ICP-AES is another technique for analyzing the concentration of metallic elements in test samples using energized atoms. ICP-AES analysis can determine elemental concentrations of trace to major, with detection limits at the parts-per-billion level for some elements.
ICP-AES analysis can be performed on solid and liquid samples, but a solid sample must be converted to liquid form before testing. Solid samples are dissolved in a solvent (typically acid) to produce a solution for elemental analysis. The sample solution is introduced into the ICP as a fine aerosol of droplets produced by a nebulizer. The plasma consists of argon gas operated at atmospheric pressure and inductively coupled to a radio frequency (RF) electromagnetic field. The spectrometer detects the atomic emissions produced. Computer software is used to control and monitor instrument functions and to process, store and output the results of the analysis.
ICP-MS analysis provides highly sensitive elemental analysis and is capable of multi-element trace analysis, often at the parts-per-trillion level. ICP-MS spectrometers can perform both qualitative analysis and quantitative analysis, and offer the following capabilities:
- Determination of a range of metals and several non-metals
- Detection and identification of trace unknowns
- Providing routine chemical testing for trace elements in super alloys and ultra-trace element analysis for high purity alloys
As with ICP-AES analysis, liquid samples are placed into the ICP by way of a nebulizer which aspirates the sample with high velocity argon, forming a fine mist. The aerosol then passes into a spray chamber where larger droplets are removed. Droplets small enough to be vaporized in the plasma torch pass into the torch body, where the aerosol is mixed with more argon gas. A coupling coil is used to transmit radio frequency to the heated argon gas, producing an argon plasma located at the torch. The hot plasma removes any remaining solvent and causes sample atomization followed by ionization.
Carbon and sulfur are easily oxidized and leave oxide gas as the metal. High temperature combustion is used to obtain the content of these elements in a material. A combination of oxygen mixed with high temperature causes the sample to combust in a furnace. The gases are passed through a series of traps, absorbers and converters to remove interfering elements and to ensure the gases have the proper structure for detection. Infrared detection is used to determine the concentration of carbon or sulfur. The infrared detector is used on the basis that various gases can absorb energy within a specific wavelength of the infrared spectrum. The amount of energy absorbed is related to the amount of the carbon or sulfur in the test sample.
Inert Gas Fusion
Inert gas fusion is used to determine the content of hydrogen, nitrogen and oxygen gases in ferrous and nonferrous materials. Gases occur as a result of melting processes and subsequent hot and cold working methods. Controlling the gas contents to low levels minimizes their adverse effects on mechanical properties such as strength and ductility. The inert gas method separates the gases from the material by reversing the bonding between them. The gas to be analyzed flows into an infrared or a thermo-conductivity detection system for quantitative analysis.
Energy Dispersive X-ray Spectroscopy (EDS)
Energy Dispersive X-ray Spectroscopy analyzes the chemical characterization of a sample by separating the characteristic X-rays of different elements into an energy spectrum. This is displayed as a histogram of the X-ray energy received by the detector, with individual peaks that are proportional to the amount of a particular element in the specimen being analyzed. EDS system software analyzes the energy spectrum in order to identify elements within the sample and determine the abundance of specific elements for semi-quantitative information.
EDS systems are typically integrated into an instrument such as an SEM with high resolution and magnification capabilities. This system can be used to find the chemical composition of materials down to a spot size of a few microns, and to create element composition maps over a much broader raster area. EDS is also helpful in identifying coatings and foreign substances on the surface of a wide variety of materials.
Portable X-ray Fluorescence Spectroscopy
X-ray fluorescence spectroscopy is a positive material identification technique that can be used for direct analysis of solid metal samples, thin metal films and various other materials. X-ray fluorescence spectroscopy is nondestructive to the sample and the portable equipment can be used for analyses in the field. This type of semi-quantitative chemical analysis uses X-ray beams to irradiate the sample. When all the energy of a primary X-ray is absorbed by an electron in an atom’s innermost electron shell, excitation and ejection of the absorbing electron occurs. The electron vacancies are filled by electrons from higher energy states, and X-rays are emitted to balance the energy difference between the electron states. The X-ray energy is characteristic of the element from which it was emitted and is directed to an X-ray detector in the XRF unit where it is recorded. The intensity of X-ray energy is compared to values for known standards to provide information about the unknown specimen.
Fourier Transform Infrared Spectroscopy (FTIR)
FTIR is used to analyze many organic materials, including plastics and other polymers. The technique produces a spectrum that provides innate details about bonding features between atoms or characteristic functional groups in a molecule.
Prior to the widespread availability of analytical instruments, quantitative chemical analysis was routinely performed by wet chemistry methods. This type of elemental analysis entails dissolving the sample and performing a specific chemical reaction with a standardized reagent for each element of interest. Although these ‘wet chemistry’ techniques are not often requested, they can be performed at Laboratory Testing Inc.
LTI Quantitative Chemical Analysis Capabilities
- Elemental analysis for quantitative and semi-quantitative results (concentration, amount or percentage)
- Trace analysis in parts-per-billion or parts-per-trillion ranges
- AMS 4081
- AMS 4083
- ASME Sect. IX
- ASTM A428
- ASTM A751
- ASTM A90
- ASTM A90/A90M
- ASTM B137
- ASTM B328
- ASTM D1976
- ASTM E1019
- ASTM E1086
- ASTM E1251
- ASTM E1409
- ASTM E1447
- ASTM E1613
- ASTM E31
- ASTM E350
- ASTM E415
- ASTM E53
- ASTM E70
- MIL Specifications