Carbon, Hydrogen, Nitrogen, Sulfur & Protein Analysis of Organic Materials

Introducción

The LECO 828/928 Series instruments are high performance combustion analyzers designed for fast, accurate determination of carbon, hydrogen, nitrogen, sulfur, and protein across a broad range of organic materials—including foods and feeds, soils and plant tissues, fuels, plastics, and fertilizers. This series provides the flexibility, precision, and productivity required for confident elemental and protein determination in modern analytical workflows.

Dumas Method for Protein Determination

The 828/928 Series determines nitrogen—and by extension, protein—using the Dumas combustion method: a quicker and less hazardous alternative to traditional Kjeldahl analysis. In this process, a precisely weighed sample is combusted in a high-temperature, whole oxygen environment, converting its nitrogen content into NO_x. The resulting NO_x is reduced to N₂ and measured by a thermal conductivity detector, providing accurate determination of total nitrogen.

Once nitrogen is quantified, the instrument applies an appropriate nitrogen-to-protein conversion factor to generate reliable protein values for foods and feeds. Because Dumas analysis requires no corrosive reagents, digestion steps, or hazardous waste handling, it delivers a cleaner, faster, and more sustainable workflow than wet-chemical methods—ideal for laboratories prioritizing speed, safety, and accurate protein results. 

How the LECO 828/928 Series Works

The LECO 828/928 Series analyzers measure elements such as carbon and nitrogen (protein) in organic materials such as foods, feeds, soils, fuels, and fertilizers. Certain models also allow for hydrogen or sulfur analysis. Both systems rely on high‑temperature combustion in a complete oxygen environment to break samples down into gases that can be measured quickly and accurately.

The 828 Series is designed for routine‑sized samples. Each sample is weighed into a tin capsule or foil and placed into a sealed purge chamber where entrained atmospheric gas is removed. The sample is then dropped into a hot, whole oxygen environment, reagent-free furnace (FP/CN), where the sample combusts rapidly. During this process, its carbon, nitrogen, and hydrogen are converted into simple gases like CO₂, NOx, and H₂O. In the FP and CN models, the combustion gases are swept from the furnace through a prechiller and thermoelectric cooler to remove moisture without chemical reagents, then collected in a controlled ballast volume. The CHN828 model includes furnace reagent in the afterburner to remove sulfur compounds from the gas stream before being collected in the ballast.

The 928 Series works similarly but is built for much larger samples (up to 3 g) and higher temperatures. Instead of capsules, samples are placed in ceramic boats and loaded into a high‑capacity autosampler. The horizontal, reagent-free furnace operates at elevated temperatures (up to 1450 °C), and an additional oxygen stream is delivered directly to the sample through a ceramic lance to guarantee complete combustion—even with bulky or difficult materials. For the FP and CN models, moisture is removed from the gas stream without chemical reagents, utilizing a prechiller and thermoelectric cooler. The analytes are collected in a controlled ballast chamber, where they stabilize before being measured. The CNS model includes an additional detector for sulfur determination.

In both systems, the combustion gases are collected in a ballast from which an aliquot is taken. This portion of the gas mixture is carried to nondispersive infrared detectors (NDIR) that detect how each gas absorbs specific wavelengths of light, and thus measures the amounts of carbon, hydrogen, and sulfur present in the sample. Nitrogen, however, is measured using a thermal conductivity detector that measures gas composition by detecting changes in heat transfer.

LECO’s Cornerstone software keeps the process moving efficiently using interleaving analysis so that one sample can be analyzed while the next is being prepared. Once analysis is complete, results are automatically calculated and reported in common units, such as weight percent or parts per million. 

Applicable Methods

LECO 828 & 928 Series conform to these approved methods.

AOAC 990.03 Crude Protein in Animal Feed

AOAC 992.15 Crude Protein in Meat, Meat Products, and Petfoods

AOAC 992.23 Crude Protein in Cereal Grain and Oil Seed Products

AOAC 993.13 Nitrogen in Fertilizer

AOAC 997.09 Nitrogen and Protein in Beer, Wort, and Brewing Grains

Instrument Support

Ensure reliable instrument performance with extensive support, training, and maintenance services. Need tailored support for your elemental analyzers? Our experts are standing by.