This technique is based on a modification of the classical Pregl and Dumas method.

Accurately weighed samples of approximately 1mg (to 3 decimal places in the mg range) in a lightweight tin capsule are dropped at pre-set intervals into a vertical quartz combustion tube maintained at 1020°C, through which a constant flow of helium is run. When the sample is introduced, the helium stream is temporarily enriched with pure oxygen. Flash combustion takes place, primed by the oxidation of the tin container. Quantitative combustion is then achieved by passing the mixture of gases over tungstic oxide. The mixture of gases is then passed over copper to remove the excess of oxygen and reduce oxides of nitrogen to nitrogen. It then passes through a chromatographic column onto a TC detector. The gases eluted are N2, CO2, H2O and SO2.

O is determined by weighing the sample into a silver capsule and heated to 1060°C. It's quantitatively converted to CO by passing over nickel-coated carbon. Any other gases are removed by passing through suitable traps.

Contact us

For more information and bookings, contact:

Applications

Both solid and liquid samples of organic and metallo-organic compounds can be analysed for %C, %H, %N, %S, %O.

Examples include:

  • Agronomy: soils, compost, seeds, plants, bumic acids, fertilisers
  • High-tech materials: carbon fibres, ceramics, glass, fibres, graphite, conductive, polymers
  • Marine science: sediments, particulate in water (filters), plankton, algae
  • Explosives: nitrocellulose, TNT, gunpowder, lead-azide
  • Petrochemistry: lubricants, oil, cake, coal, gasoline
  • Various materials: inorganic and organic pigments, dyes, cement
  • Synthetic materials: polymers, rubbers, tyres, fibres
  • Metallurgy: stainless steel, carbon steel, nitrides, carbides, metal powders
  • Environmental: particulate in air (filters), waste material, compost, sewage sludge
  • Food and beverage: beer, soy sauce, instant noodle paste, milk, infant formula, juices.

Equipment and location

Equipment

Our FLASH 2000 CHNS/O Analyzer can analyse for C, H, N, S and O.

The facility also houses a microbalance which measures grams to six decimal places.

Visit ThermoFisher Scientific's website for more product information.

Location

Molecular Biosciences Building (Building 76), Room 345-A

Sample requirements

Requirements

A minimum 5mg sample is required as samples are run in duplicate and a further 2mg if O is required. Use screw-cap tubes to preserve your sample. If samples are difficult to remove due to electrostatic charge etc, then you'll need at least twice that amount. Samples must be clean (no foreign particles) and dry. If you send samples by post, they should be in plastic containers with sealed lids.

Preparation

Many materials are often inhomogeneous, and an appropriate homogenisation procedure is therefore required.

Note: the reproducibility of results is independent of the sample size but strongly dependent of the sample homogeneity.

Dry and soft materials

Samples of cereals, dry bread, plant tissues, etc: grind the sample in a rotor mill equipped with a 1mm sieve, possibly with trapezoidal holes. According to AOAC 992.03 method, the suitable fineness of grind is that which gives relative standard deviation (RDS) < 2% for 10 successive determinations of nitrogen.

Dry mixtures of hard, soft and tough materials

Samples of rock-containing soil, shale, mining slags, etc: first use a crushing mill to crush the hard particles and then mix them with the rest of the sample; in some cases you'll need to carry out a second grinding process in a ball mill.

Dry or wet soft materials

Meat, sausages, fish meat, etc: grind in a knife mill with liquid nitrogen. Place the sample in the mill, add liquid nitrogen, wait about one minute, add liquid nitrogen again and start the mill. Thanks to the action of liquid nitrogen, the sample is immediately frozen at -195°C and becomes very brittle and fragile. A mild grinding action is then enough for the complete destruction of the texture of the sample, and the heat generated by the mill action won't affect the water content as it will be adsorbed by the nitrogen evaporation.

Rape-seeds and other oil-containing seeds, which become smeary when ground at room temperature, form a homogeneous dry powder. Meat, fresh plant tissues and similar wet products form a homogeneous paste.

When liquid nitrogen isn't available, it's possible to freeze the sample (at least -25°C, minimum 1 hour) and to grind it when deeply frozen.

Materials containing volatile compounds

Sometimes it's important that the material to be ground doesn't lose volatile constituents or take up moisture. Liquid nitrogen, which is added to the container, is quite dry, and all moisture in the sample is immediately frozen and can't escape. When liquid nitrogen is volatilised from the container, the sample is still so cold that no volatile constituents are volatilised. After shaking, the container is allowed to warm up to room temperature unopened so that no atmospheric moisture can condense on the cold sample. The homogenised sample has the same moisture content and the same content of volatile constituents as the original material.

Tool Sample type
Mortar (agate or porcelain) Coals, soils
Coffee mill Cereals, barley, meal
Hammer mill Textiles, paper
Ball mill* Solids (coals, cokes)
Ball mill + liquid nitrogen Hard materials (bones, textiles, hair), wet products (meat, fresh vegetables)
Rotor speed mill** Cereals, plants, plastics, synthetic resins, soils, animal feeds, drugs, grain, coal, fertilisers
Scissors, blades Leaves, fibres, plastic products, rubbers

* The microdismembrator is a very strong, longitudinally shaking ball mill. The materials to be ground are placed into an egg-shaped Teflon container together with 2 to 4 steel balls, which should have different diameters, usually 10mm and 7mm.

** The samples are ground by the impact and shearing stresses from the high-speed rotor and are forced through the sieve by the ultra-centrifugal force. The ground material is collected in a collecting vessel. It's possible to grind up to 0.5-1mm particle size.

Sample analysis and submission

Submission

External users

Contact us for booking instructions and paperwork.

You'll need to raise a purchase order.

School users

Use our online Science Booking Calendar (UQ log-in required) to book in your samples.

Select 'Microanalytical service' from our School's equipment menu, and ensure you complete all fields.

You'll also find booking instructions, and a link to an RISQ form, which you'll need to complete.

Once you've completed the necessary paperwork, leave your sample in the tube rack labelled 'Microanalytical Service', in the foyer of Level 5 of the Chemistry Building (Building 68).

Data analysis

We usually carry out analysis on Thursdays and Fridays. We can usually email you the results on the same day.

Accuracy for CHN, CHNS and O determinations
Theoretical value Experimental value Error
0.10% 0.10% 0.01
1% 1% 0.02
10% 10% 0.1
50% 50% 0.3
90% 90% 0.3

Charges and considerations

Charges

Prices (excluding GST) per sample:

  • School users: $24 for C, H, N, S; $24 for O; $48 for C, H, M, S and O, total of 5 samples required
  • Non-School users: $60 for C, H, N and S, $60 for O; $120 for C, H, N, S and O 
  • Next-day express service: $120 for C, H, N and S or $120 for oxygen; we can only do one type of analysis per day.

Considerations

UQ users have priority of access.

You'll need to undertake the relevant building and other inductions before using equipment.