The Technique

The technique used is based on a modificationof 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 preset intervals of time into a vertical quartz combustion tube maintained at 1020 deg.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, SO2.
O is determined by weighing the sample into a silver capsule and heated to 1060 deg.C.  It is quantitatively converted to CO by passing over nickel coated carbon.  Any other gases are removed by passing through suitable traps.

Applications

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

 

Facilities Available

The instrument is a FLASH 2000 CHNS/O Analyzer
FLASH 2000 CHNS/O Analyzers
which can analyse for C,H,N,S,O. The facility also houses a microbalance which measures grams to 6 decimal places.

Sample 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 at least twice that amount will be required.  Samples must be clean (no foreign particles) and dry.  If samples are sent by mail they should be in plastic containers with the lids sealed.

Sample preparation

Many materials are very often unhomogeneous, and an appropriate homogenisation procedure is therefore required. Important: the reproducibility of results is independent of the sample size but strongly dependent of the sample homogenity.
Dry and soft materials
Samples like cereals, dry bread, plant tissues, etc.: grind the sample in a rotor mill equipped with a 1 mm. 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 determination of nitrogen.
Dry mixtures of hard, soft and tough materials
Samples like rock-containing soil, shale, mining slags, etc.: a crushing mill is first of all to crush the hard  required the hard particles and to mix them with the rest of the sample; a second grinding process in a ball mill is also required in some cases
Dry or wet soft materials
Materials like meat, sausages, fish meat, etc.: grind in a knife mill with liquid nitrogen. Place the sample in the mill, add liquid nitrogen, wait about 1 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 extremely 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 will not affect the water content because 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 is not available, it is 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 is important that the material to be ground does not 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 cannot escape. When liquid nitrogen is volatilized 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 homogenized 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, fertilizers
Scissors, blades Leaves, fibers, plastic products, rubbers

 

 

Notes:
(*) The microdismembrator is a very strong, longitudinally shaking ball mill. The materials to be ground is placed into an egg-shaped teflon container together with 2-4 steel balls, which should have different diameters, usually 10 mm and 7 mm diameter.
(**) 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 is possible to grind up to 0.5-1 mm particle size.
 

 

Sample submission

Samples are to be submitted on-line using the booking calendar SCMB_Microanalytical_Service, completing all fields and referring to the booking instructionsLeave your sample in tube rack labelled 'Microanalytical Service', in the foyer of Level 5 of Building 68.
RISQ is required for non-school UQ memebers or Purchase Order for all other customers

Analysis of data

Analysis is normally carried out on Thursdays and Fridays.  Results can be emailed to the customer, usually on the day of the analysis.

 

 

 

 

 

 

Charges

Prices per sample:
SCMB users - $24 for CHNS;  $24 for Oxygen; $48 – CHMS&O, total of 5 samples required
Non-SCMB users - $60 -CHNS, $60 – Oxygen; $120 – CHNS&O
Next day Express service: $120 –CHNS or $120 – Oxygen; only one type of analysis is possible per day
Prices exclude GST

Contacts

Michael Nefedov: m.nefedov@uq.edu.au; 0427428089, 07-33651833
;

George Blazak g.blazak@uq.edu.au;

David Rosolen david.rosolen@uq.edu.au

 

 

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