Analytical Services
for Elemental  Analysis

 

Elemental Analysis 
Our three dedicated elemental analysers routinely determine carbon, hydrogen, nitrogen, oxygen and sulfur in a wide range of organic and inorganic materials. Skilled technicians analyse these elements from high percentages down to less than 0.01% on solid, liquid, or even gaseous samples. We also determine total organic carbon (TOC), total inorganic carbon (TIC), and protein.

Elemental analysis (also known as elemental microanalysis) is a reliable and cost-effective technique used to assess the purity and chemical composition of research compounds or to provide information of the composition of materials.

In percentage elemental analysis (EA) of CHNSO, milligram amounts of samples are combusted or pyrolysed at high temperature in a helium carrier gas. After suitable preparation the measurable gases (CO2, H2O, N2, SO2, or CO) are separated on a chromatography column. The gases are passed in turn through a thermal conductivity detector (TCD) where the gases are quantified against known reference standards.

 

Sample Delivery Address
OEA Laboratories Ltd.
Unit 1A-1D
North Road Industrial Estate
Okehampton
EX20 1BQ

 

Sample submission forms:

- Organic analysis

- Inorganic analysis

CHN

This is probably the most common elemental analyser configuration which determines total carbon, hydrogen and nitrogen simultaneously. It is well suited to the analysis of most organics and inorganics from 0.01% to high percentage levels. The CHN method is limited to the analysis of relatively small sample weights because the resolution of the nitrogen and carbon peaks can be compromised.

CHNS

The CHNS mode for elemental analysers determines total carbon, hydrogen, nitrogen and sulphur simultaneously from 0.01% (0.05% for sulphur) to high percentage levels. It is ideal for the analysis of most sulphur compounds and is widely used in the analysis of soils, sludges and plant material. As with the CHN method the analysis for CHNS is limited to relatively small sample weights because the resolution of the nitrogen and carbon peaks. Where sulphur is required at levels of less than 0.05% the sulphur method should be selected which allows the use of even larger samples or the more sensitive flame photometric detector (FPD).

 

NC

The NC mode determines total nitrogen and carbon simultaneously from 0.001% (depending on sample types and weights) to high percentage levels. The method is reliable for almost all organic and inorganic compounds and is ideally suited to the analysis of plant material, animal tissue and soil samples. Unlike CHN or CHNS analysis the NC method has almost unlimited resolution of the nitrogen and carbon peaks which allows the analysis of much larger samples.

 

N

The N mode determines total nitrogen from 0.001% (depending on sample types and weights) to high percentage levels. Protein can also be determined by this method. The use of large combustion tubes fitted to the elemental analyser allows protein determination on higher weights. The method is reliable for almost all organic and inorganic compounds and is ideally suited to the analysis of plant material, animal tissue and soil samples. The N method has almost unlimited resolution of the nitrogen which allows the analysis of much larger samples.

 

NCS

The NCS mode determines total nitrogen, carbon and sulphur simultaneously from 0.01% (0.05% for sulphur) to high percentage levels. The method is reliable for almost all organic and inorganic compounds and is often applied to the analysis of plant material, animal tissue and soil samples where hydrogen analysis is not required. The method has some of the drawbacks of the CHNS method but can run slightly larger samples as it is not prone to water saturation. Where sulphur is required at levels of less than 0.05% the sulphur method should be selected which allows the use of even larger samples or the more sensitive flame photometric detector (FPD).

 

S

The S mode determines total sulphur from a few 10’s of parts per million to high percentage levels depending on the sample type and the detection system used in the elemental analyser. The method is reliable for almost all organic and inorganic compounds and is often applied to the analysis of oils, minerals, plant material, animal tissue and soil samples. The method has none of the drawbacks of the CHNS and NCS methods so it can run larger samples. Where the S values are likely to be very low (in soils for example) it is possible to use higher sample weights, increase the gain of the instrument to achieve a better signal to noise ratio and/or switch to the more sensitive flame photometric detector (FPD).

 

O

The O mode determines total oxygen from 0.01% (depending on sample types and weights) to high percentage levels. The method is generally applied to organic compounds but it can determine oxygen in many inorganic materials. The O method has almost unlimited resolution of the oxygen peak which allows the analysis of larger samples when required. Where the oxygen values are likely to be very low it is possible to use higher sample weights and/or increase the gain of the instrument to achieve a better signal to noise ratio.

 

TOC / TIC

If inorganic carbon is present it can be eliminated by direct acidification with dilute hydrochloric acid or indirectly by exposure to concentrated sulphurous acid vapour. Where samples are submitted for total organic carbon (TOC) we will pre-treat your samples in this way to remove any inorganic carbon. Total inorganic carbon (TIC) is determined by difference from the total carbon and total organic carbon values.

 

Sample Preparation for % CHNSO Elemental Analysis

One of the great advantages of elemental analysis is the relatively small sample weights that are required for analysis. The sample weights used will vary according to the application, the sample type, detection limits and precision that needs to be achieved. Detection limits will normally be in the order of 0.01% or better but lower detection levels or precision can often be achieved by changing the analytical mode, increasing the sample weight and/or increasing the gain to achieve a better signal to noise ratio.

Please see below our weight guide to the sample sizes we require (per run) for each type of determination. Larger samples are preferred because our analysts must be able to recover sufficient sample from the vial to transfer into small capsules. It is very useful for us to have more sample to allow us to run random QC check samples. This also ensures that we can keep our sample turn-around on schedule should we have any problems with our instrumentation or encounter other unforeseen failures. We can return unused sample upon request.

Sample preparation might be required to obtain the best representation at the recommended weight levels. Unless otherwise requested samples are analysed ’as received’.

Samples must be free from residual solvents or moisture to provide reliable results. Depending upon the sample type, samples should dehydrated by freeze drying or vacuum oven drying to constant weight. Samples should be finely ground using a mortar & pestle or a ball mill to ensure that the sample is representative at the target sample weight.

If inorganic carbon is present it can be eliminated by direct acidification with dilute hydrochloric acid or indirectly by exposure to concentrated sulphurous acid vapour. Where samples are submitted for total organic carbon we will pre-treat your samples in this way to remove any inorganic carbon. Total inorganic carbon (TIC) is determined by difference from the total carbon and total organic carbon values.

We are able to prepare or pre-treat your samples at additional cost. We are able to accurately determine loss of weight on drying (on a micro scale) where required. Please contact us to discuss any aspects of sample preparation that you may require.