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Skidmore College
Stable Isotope and Palæoclimate Analysis Laboratory

Analytical services: elemental composition of combustible material

The SPA lab analyzes the elemental mass and composition (carbon, nitrogen, hydrogen and oxygen) of combustible material using a Costech Elemental Combustion System (ECS) 4010 elemental analyzer (EA). Sample material is packed in air-free tins and combusted at high temperature in the presence of abundant oxygen.  Combustion gases treated and scrubbed in accordance with the elements which are being determined. Next, the gases are separated in time using a GC column. Once gases are separated, a thermal conductivity detector (TCD) provides information on the percent composition of carbon, nitrogen, hydrogen and sulfur in the resulting gases and sample. For carbon and/or nitrogen elemental composition analysis, we often use the MAT-253 as the mass detector and provide roughly normalized isotopic results as well free of charge. Oxygen composition of solids and liquids can also be analyzed using a pyrolysis reaction, higher flash oven temperatures and different column reagents, though a TCEA is a better machine for oxygen analysis. The SPA lab has the capability to analyze for the mass of sulfur but does not routinely perform that analysis; contact us if you would like to analyze for sulfur.

A compositional standard is used to create a standard curve for estimating elemental mass and percent composition. Generally, 5 or 6 replicates of varying mass will be required for a percent composition standard. For research analyses, Acetanilide or NIST 1547 (peach leaves) display the greatest homogeneity in percent composition for both carbon and nitrogen and are obtainable in much larger quantity than other standards.  USGS-40 (glutamic acid) could be used where the highest quality and recognition of analytical quality is required, e.g., methodological studies. However, a substantial amount of standard is required for percent calibration; based on the limited supply of international standards, any possibility of using an in-house standard for percent composition should be considered. Four replicates of an in-house standard are scattered through the run to provide analytical precision and track machine performance. The first 2 autosampler slots are usually left blank as conditioning samples to flush out the GC and columns. The following two slots will be used as blanks and filled with empty, crushed sample tins. These “blanks” will be used to adjust for background nitrogen content of the auto sampler and oxygen injection. If room allows, a blank at the end of the run will measure any changes in nitrogen background through the run.

Elemental composition (CHNOS) of combustible material rates

Element Phase Quantity Measurement Precision Internal External
CHNS Solid 0.1–10 mg ± 0.3 % $6* $10*
O Solid 0.1–10 mg ± 0.3 % $8* $13*

Sample types: combustible solids, dried liquid residue, glass\quartz filters

*Price is for pre-weighed and packed samples. Un-massed material requiring drying, weighing, or other processing will incur an additional charge. Massing and packing is a flat $1 fee.   

Sample requirements: The minimum mass of an element that we can detect with 0.3% precision is 7 µg.  Elemental masses down to 2 µg are analyzable with poorer precision. Samples should be dried (50–60oC) and often ground and homogenized; however, we will analyze material in any way your field finds acceptable. Samples pretreated with acids should be rinsed several times with distilled water. We can load your samples into tins ($1/sample); ship in a secure container. If you prefer, you may load your own samples into the proper size tin capsules; use the smallest capsule size that will hold the sample with no leakage. Capsules should be folded and crushed into a cube or ball without any protrusions. Filters should be shaped into cylinders less than 5 mm in diameter. Record the final weight after the capsule is sealed. To prevent leakage during shipping, cover the loaded samples (with tin foil, parafilm, index card, etc) under the 96-well full plate cover. When designing your runs, keep in mind that our autosampler has 49 usable positions.

Material captured on filters may be analyzed. Quartz filters are very much preferred, but normal glass fiber filters (Whatman GF/F or Pall A/E) are acceptable. The largest filter we can run whole is 25 mm diameter. If you would like elemental mass results, please provide the mass of material on the filter, not the total mass of filter and filtrate. You may cut larger filters (e.g. 47 mm) in half and run them as two separate samples; the accuracy of the mass estimates will be affected to an unknown degree by how much loss of sample mass there is due to cutting.