TOC TOTAL ORGANIC CARBON
TOC Total Organic Carbon analysis
In addition to our ISO 17025 accredited CHNOS analysis services, our laboratory also specialises in Total Organic Carbon (TOC) analysis.
TOC analysis in the laboratory is the measurement of organic carbon. This is mainly in soils and sediments but in theory could be applied to any solid substance containing a mixture of organic and inorganic carbon.
This measurement of TOC should not be confused with the TOC analysis of organics in water which is a different field and uses different analytical instrumentation.
Soil Organic Matter (SOM) and TOC
Soil Organic Matter (SOM) is an important indicator of soil quality for several reasons including:
· Nutrient availability
· Improved soil structure and stability
· Water retention/draining
· Habitat for soil microorganisms
There is no laboratory test to directly quantify SOM; TOC analysis of your soil sample will tell you the % organic carbon (soil organic carbon) present in your SOM.
One commonly utilised method to measure TOC is to differentiate between TC, TIC and TOC (Total Carbon, Total Inorganic Carbon and Total Organic Carbon) using combustion elemental analysis (sometimes referred to as dry combustion):
· Analyse the dried and ground sample “as is” to give TC (Total Carbon)
· Acidify a portion of the sample – this drives off the TIC (Inorganic Carbon) leaving only the organic carbon
· Analyse this portion for TOC
· Thus we have TC, TOC and TIC (TIC = TC-TOC)
Sample Preparation Process
- Samples are precisely weighed into silver boats or capsules that have been acidified by 1:1 hydrochloric acid and digested at 80°C.
- This eliminates carbonates as carbon dioxide.
- After final encapsulation samples are dropped at pre-set times into a combustion tube (at 1000°C). A constant stream of helium is maintained through the tube.
- Helium stream replaced by pure oxygen for a brief period prior to sample introduction.
- Sample is instantaneously burned.
- Resulting combustion gases passed over catalysts to ensure complete oxidation and absorption of halogens, sulfur and other interferences.
- Carbon dioxide separated from other unwanted gases on a chromatographic column and quantitatively measured by a thermal conductivity detector.
The technique is generally free of interferences.
- A few silicon and organo-metallic compounds exhibit a tendency to form stable carbides.
- Samples containing phosphorus may not combust successfully and give low carbon values.
- All of these problems can be remedied with the addition of additives to the sample, including most inorganic compounds such as carbides and nitrides.