Instrumental Chemistry

ICP Analysis, Positive Material Identification, Carbon Analysis & More

Instrumental chemistry, also called instrumental analysis or instrumental analytical chemistry, can provide valuable information about the make-up or elemental composition of a test sample. Instrumental analysis can provide qualitative results by identifying individual elements or groupings of elements in the sample and/or quantitative information by determining the amount of each included element. The results of instrumental chemistry can be used in many applications including the following:

• Verification of conformance to a standard or specification (ASME, MIL, ASTM)
• Positive material identification
• Evaluation of raw materials
• Detection of impurities
• Identification of the alloy used to make a specific component
• Trace element analysis

There are a variety of analytical chemistry techniques performed with instruments that provide automated and computerized processing and reporting of results, including ICP Analysis, Atomic Emission Spectroscopy, Energy Dispersive Spectroscopy (EDS), portable X-Ray Fluorescence Spectroscopy (XRF), the Combustion Furnace method of sulfur and carbon analysis, and Inert Gas Fusion for hydrogen, nitrogen, oxygen determination. Laboratory Testing Inc. offers complete elemental composition analysis with quantitative and qualitative results, including trace element analysis performed by ICP spectrometers with detection limits in the “parts per trillion” range for some elements. The most appropriate method of instrumental analysis often depends on the type of sample, quantity of material available for analysis, desired result and cost constraints.

The Instrumental Chemistry Processes

Atomic Emission Spectroscopy

Atomic Emission Spectroscopy (AES) is one of the most useful analytical chemistry techniques for direct analysis of elemental composition in solid metal samples. LTI’s AES spectrometers can analyze all common elements in metal and alloy samples, including soft metals such as tin, lead and zinc.

The basic principle of AES says that when free atoms are put into an energetic environment, they emit light in a series of wavelength bands, similar to the diffraction of light into a rainbow. These wavelength bands or emission lines form a pattern that is characteristic of the atom that produced it. Generally, the intensities of these characteristic lines are proportional to the number of atoms producing them. Consequently, the elemental composition can be identified qualitatively and quantitatively by the types and intensities of the emission lines.

The AES systems at LTI have a spark source to create the energetic environment. When the spark strikes the sample, rapid heating of the sample occurs and it vaporizes. The vaporization produces the spectrum of lines from the elements that are present in the sample. The spectra are analyzed using a diffraction grating and a set of photomultiplier tubes to identify the elements and measure their concentrations.

ICP Analysis

ICP analysis is performed at LTI with top-of-the-line computer-controlled spectrometers. The computer software is used to control and monitor instrument functions and to process, store and output the results of the instrumental analysis performed by the spectrometer.

Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) is a technique that can detect most of the elements in the periodic table and can determine elemental concentrations of trace to major. Reliable results can be obtained for about 70 elements with detection limits in the parts per billion range. The basic principal of AES explained earlier also applies to this type of instrumental analysis, but the excitation source is inductively coupled plasma. The plasma consists of argon gas operated at atmospheric pressure and inductively coupled to a radio frequency (RF) electromagnetic field. The sample is a solution of the test material that is introduced into the ICP as a fine aerosol of droplets produced by a nebulizer. The system contains a torch made up of a set of concentric quartz tubes that contain the argon used for the plasma, for cooling the torch and for guiding the test sample to the plasma. The RF generator supplies the high-frequency alternating current in the induction coil and sustains the inductive coupling of energy into the plasma.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) combines the easy sample introduction and quick analysis of ICP technology with the accurate and low detection limits of a mass spectrometer. This method is highly sensitive and capable of trace multi-element analysis, often at the parts-per-trillion level, as well as determination of a range of metals and several non-metals. ICP-MS also analyzes aqueous samples that are introduced 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. Samples are decomposed to neutral elements in a high-temperature argon plasma to produce ions and are analyzed based on their mass to charge ratios.

X-ray Fluorescence Spectroscopy

X-ray Fluorescence Spectroscopy (XRF) is a nondestructive technique performed at LTI using portable equipment that can provide direct analysis of solid metal samples for major elements, thin metal films, and can be used for RoHS screening of metallic and non-metallic samples.

An X-ray tube is used to irradiate the sample with a primary beam of X-rays. Some of the X-rays are absorbed by the sample elements causing excitation, then fluorescence occurs as X-rays are emitted with an energy that is characteristic of the element from which it was emitted. The fluorescence X-rays are collimated and directed to an X-ray detector. The energy of each X-ray and number of X-rays at each energy level are recorded. The X-ray intensities at each energy level are compared to values for known standards for quantitative analysis of the unknown specimen and positive material identification.

Combustion Method for Carbon and Sulfur Analysis

High temperature combustion is used for carbon analysis and sulfur analysis to determine their content in a variety of metal and inorganic materials. The test begins by heating a sample in a high-temperature furnace which is flooded with oxygen, causing the combustion of the carbon and sulfur in the sample. 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 the carbon or sulfur. The infrared absorption detector measures the absorption of the infrared wavelengths characteristic of carbon and sulfur. The amount of energy absorbed is related to the amount of the carbon or sulfur in the test sample.Lower detection limits for carbon range from 0.1 to 10 parts per-million with upper detection limits of 2.5 – 3.5 %. Lower detection limits for sulfur range from 1. to 50 parts per-million with upper detection limits of 0.2 – 2.5 %.

Inert Gas Fusion

Inert gas fusion is a quantitative instrumental chemistry technique for determining the concentrations of gases (nitrogen, oxygen, and hydrogen) in ferrous and nonferrous materials. These gases are found in materials as a result of melting processes and subsequent hot and cold working methods. Managing the gas contents at low levels minimizes their adverse effects on the materials’ mechanical properties.

The inert gas method heats the sample to a molten state in a fusion furnace with an inert gas atmosphere and reverses the bonding between the gases and metals, causing the dissociation of the gases. The fusion gases are separated and carried to a detector. An infrared detection system is used at LTI to detect oxygen, and a thermo-conductivity system is used to detect nitrogen and hydrogen.

Providing Samples for Analytical Chemistry

To save time and money and to assure that the results are as accurate as possible, we ask customers to provide us with as much information as possible about samples submitted for analytical chemistry. The information will help us choose the most appropriate and cost-effective testing methods, and may eliminate the need to run preliminary tests that could delay results and increase costs. Whenever any of the following information is available, please include it on your purchase order or with your test sample.

• Sample Composition -  Since LTI performs analyses on a relatively large number of metal alloys, when a customer asks for the analysis of only one component of the alloy without giving us the approximate composition of the sample, it is possible that errors could result due to unknown interferences. These errors can be related to interference of one of the elements with others in the alloy due to the analytical chemistry method used.
• Standards & Specifications -  When testing is performed to determine if a sample conforms to a standard or specification (e.g. ASME, ASTM, MIL), it is important to know the alloy or grade that is being tested because some standards refer to more than one alloy or grade.
• Sample Size -  To assure that we have an adequate sample size to perform the required analytical chemistry tests, we provide the following guidelines:
  • The sample should be 1/8” thick and 1” x 1” square for AES of solid samples.
  • When AES analysis for gases is required, the sample size is weight dependent. For carbon and sulfur the sample should weigh a minimum of 2 grams, for nitrogen and oxygen the sample should weigh a minimum of 1½ grams and for hydrogen the sample should weigh a minimum of 2 grams.
  • Samples that require ICP analysis should weigh a minimum of 5 grams.

Note: For comparison, a dime weighs about 2½ grams and a nickel weighs about 5 grams.

LTI Instrumental Analysis Capabilities

• Atomic Emission Spectroscopy
• ICP Analysis
  • ICP Mass Spectrometry (ICP-MS)
  • ICP Atomic Emission Spectroscopy (ICP-AES)
• X-ray Fluorescence Spectroscopy for positive material identification
• Combustion Furnace Method for Carbon and Sulfur Analysis
• Inert Gas Fusion for Oxygen, Hydrogen & Nitrogen Analysis