The Benefits of Combustion Analysis Over Spectrometric Methods for C/S and O/N/H Measurements

In this interview, AZoM talks to Dr. Andre Klostermeier, product manager at ELTRA, about the benefits that combustion analysis has over spectrometric methods for C/S and O/N/H measurements.

Can you give a brief overview of ELTRA, and the types of products you produce?

Since its foundation in 1981, ELTRA develops and manufactures powerful combustion analyzers used for elemental analysis of a wide range of organic and inorganic solid materials. The instruments ensure reliable, reproducible and highly precise measurements of carbon, sulfur, oxygen, nitrogen and hydrogen concentrations. In 2007, thermogravimetric analyzers were added to the product portfolio. Today, ELTRA is one of the leading manufacturers of combustion analyzers worldwide.

Can you please explain the basic theory behind combustion analysis?

As the term suggests, the combustion of a solid sample is an essential step in combustion analysis. This can be done in various furnace types with temperature ranges from 1550 °C max. (resistance furnace) to 3000 °C (impulse furnace). The use of the furnace depends on sample characteristics, e.g. if the material is organic or inorganic, and whether carbon/sulfur or oxygen/nitrogen/hydrogen concentrations are to be measured.

This method is best explained by giving an example. To measure the carbon and sulfur content, the sample is melted in a pure oxygen atmosphere in an induction furnace, causing sulfur to react to sulfur dioxide (SO₂) and carbon to a mixture of carbon monoxide (CO) and carbon dioxide (CO₂). The combustion gases pass through a dust filter and moisture absorber for purification. In the next step, the sulfur dioxide is detected in infrared cells. Oxidation of both, carbon monoxide to carbon dioxide and sulfur dioxide to sulfur trioxide follows the sulfur measurement. The SO₃ gas is removed with cellulose wool; the carbon content is detected by infrared cells which can be individually customized.

What are the benefits of combustion analysis compared to other analytic methods?

In contrast to other analytical methods for measuring element concentrations in solids, like XRF, spark OES, GD OES or ICP OES for liquid/dissolved samples, combustion analysis provides a working range for C/S and O/N/H  concentrations from <1 ppm up to 100%. Particularly in the low ppm range, combustion analysis is the only technique capable to provide truly reliable measurement results for solid samples. 

With the combustion technique, it is possible to analyze inhomogeneous samples or samples with carbon impurities, like grey cast iron, quickly and reliably without time-consuming sample preparation. Pins, rings, wires, powders, granulates or any other solid sample shape can be directly applied to a C/S or O/N/H combustion analyzer. Spectrometric methods like spark OES require a sample with a plane surface to deliver correct results.

Combustion analyzers offer the benefit of simple and fast analysis with high sample weights up to several grams. The results are usually available within minutes, depending on the method used, allowing for high sample throughput. 

Are there applications that can only be done with combustion analysis?

Combustion analyzers not only measure the total element content of C/S and O/N/H but also the fractions. A typical example of fractional analysis is the measurement of Total Organic (TOC) and Total Inorganic Carbon (TIC) in samples like soil or waste. These fractions are measured by applying different temperatures during combustion or by acidification of samples.

For ceramic samples like silicon carbide or tungsten carbide, combustion analyzers distinguish the free, bound and total carbon content. Other examples are analysis of the surface carbon content of copper and steel tubes, or fractional oxygen analysis of steel where oxygen can be bound to iron or other metals like manganese or silicon which are part of the iron ore veinstuff.

Why is knowledge of element concentrations (C/S and O/N/H) important?

The concentration of these elements can have a substantial influence on material properties and therefore needs to be measured accurately and reliably as part of the quality control process, or for environmental purposes. Here are some typical examples:

Metals: The content of C/S and O/N/H influences properties such as ductility, corrosion tendency, or brittleness of almost any metal (e.g. steel, iron, copper, titanium, nickel). Only if the element concentrations are within the specified range, will the material have the desired property, e. g. a medical stent will last a long time in a human body.

Soil: In soil, carbon is present in different bonding forms. Total organic carbon (TOC) and total inorganic carbon (TIC) are suitable standard parameters to characterize, for example, the fertility of soils.

Coal: The carbon value of coal defines its calorific value.

Ceramics: The carbon content can be an indication of the purity of a technical ceramic-like silicon carbide. A combustion analyzer precisely measures the carbon content and thereby also determines, for example, the SiC content in refractory materials as the only source of carbon.

Which industries benefit most from combustion analysis?

ELTRA’s Elemental Analyzers are used in many different industries. Among the most important ones are metalworking, cement, aerospace, mining, and steel. But our instruments are also found in sectors like medical engineering or environmental analysis. 

The ELEMENTRAC CS-i is ELTRA’s latest analyzer. What are the benefits of using the CS-i compared to any other carbon/sulfur analyzer on the market?

The ELEMENTRAC CS-i boasts the widest working range for carbon/sulfur measurement in the market and is suitable for analyzing standard samples like steel, copper, cast iron, refractories as well as complex sample matrices. Moreover, tools like ramping or the possibility to apply reduced analysis power ensure correct C/S analysis of intensely burning samples like magnesium or tin.
Fine ceramic powders, for example, are challenging due to the danger of sample loss during combustion. The unique intelligent lance management implemented in the CS-i ensures a safe and reliable combustion process without sample loss. The wide working range guarantees precise C/S analysis of samples with high element concentrations like carbides, sulfides, copper concentrates.

Like all ELEMENTRAC analyzers, the CS-i offers freely selectable configuration of each IR cell, allowing for optimum measuring conditions for each application. With the CS-i it is possible to determine both high and low carbon and sulfur concentrations in one single measurement.

The ELEMENTS software is an essential part of the ELEMENTRAC analyzers. What are the key functionalities?

Elemental analyzers are usually operated with an external PC and software. ELTRA’s new ELEMENTS software comes with all ELEMENTRAC models which are CS-i, CS-d, and ONH-p. The innovative ELEMENTS software has a well-structured, modern design and guarantees fast and traceable analysis processes. A central window (analysis and results) is the starting point from which all functionalities required for the daily routine are easily accessible. Key functionalities include report functions, export to LIMS, diagnosis tools, and a leakage test.

What’s next for ELTRA?

We are constantly striving to improve our instruments and develop both hardware and software to explore new fields of applications. The upgrade of our existing C/S and O/N/H analyzer range to the new ELEMENTRAC design and technology will continue for the next couple of years. To stay up to date on new product releases, webinars and application information, we recommend signing up to our customer newsletter which is sent 3 to 4 times per year.

About Dr. Andre Klostermeier

Dr. Andre Klostermeier studied chemistry at Westfaelische Wilhelms University in Muenster (Germany) and graduated with a Diploma in Chemistry followed by a Ph.D. in Analytical Chemistry. He worked as a sales and product manager as well as in application development for combustion analyzers and GD spectrometers for various companies. Dr. Klostermeier joined ELTRA in 2013 as a product manager for the whole combustion analyzer range.