The Elemental Analyzer (EA) is a dumas (flash) combustion peripheral coupled to an isotope ratio mass spectrometer and used to measure:

δ¹⁵N and δ¹³C of a wide range of organic matter.

At UCSC, the EA is primarily used to simultaneously measure δ¹⁵N and δ¹³C of organic matter (e.g., muscle tissue, algae, kelp, collagen, hair). The facility has an EA dedicated to running ¹⁵N enriched samples primarily from samples collected on glass fiber filter (GFF) media.

Solid materials are analyzed for δ¹⁵N and δ¹³C isotopes using either a Carlo Erba 1108 or a CE Instruments NC2500 elemental analyzer interfaced to a ThermoFinningan Delta Plus XP isotope ratio mass spectrometer (IRMS). Tin (or silver) encapsulated samples are flash (Dumas) combusted at 1020°C in a quartz column containing chromium oxide (acting as an oxygen source to aid combustion) and silvered colbatous/cobaltic oxide (acting as a scrubber to "clean" the combustion products of sulfur bearing compounds and halides). Following combustion, excess oxygen and oxides of nitrogen are reduced in a reduction column (reduced copper at 650°C). Helium carrier flows through a water trap containing magnesium perchlorate. N₂ and CO₂ are separated on a Carbosieve GC column (45°C, 100 mL/min) before introduction to the IRMS.

During analysis, calibrated in-house standards precede and are interspersed between samples to correct for linearity (size) effects and drift. A second calibrated laboratory standard is run "as-a-sample" to monitor quality control and long-term performance. These laboratory standards, which are selected to be compositionally similar to the samples being analyzed, have been previously calibrated against NIST Standard Reference Materials (IAEA-N2, IAEA-N3, IAEA-USGS25, and IAEA-USGS26 of δ¹⁵N and IAEA-CH7, and NBS-22 and IAEA-USGS25 for δ¹³C).

Corrected delta values are expressed relative to international standards PDB (PeeDee Belemnite) for δ¹³C and Air for δ¹⁵N.

Sample Size: The amount of sample required depends on the amount of carbon and nitrogen in the material. A sample should contain between 20-150µg N (60µg optimal size) and 200-2000µg C (60µg optimal). If the two of %N, %C and/or the carbon-to-nitrogen (C/N) ratio is know then you can use the tool below to guide the appropriate sample size for the instrumetation.

Run configuration: A Run Setup Tool is has been developed to aid in preparing standards for a run.

Homogenization: Many samples, such as fish muscle, leaf disks, root sections, small insects, fish scales, etc., that meet the target weight can be encapsulated whole in tin capsules. Some samples (e.g., fish muscle) may need to be stripped of organic oils depending upon the scientific question. Heterogeneous samples such as leaves or coarse materials, such as soils or sediments requires homogenization by grinding using a mortar and pestle or automated grinder.

Inorganic carbon removal from soils and sediments (2 methods): Sample containing both organic and inorganic carbon, generally inorganic carbonates, will combine to yield a mixed organic and inorganic δ¹³C value, if inorganic carbon is not removed prior to analysis. Inorganic carbon is often a component of ocean or lacustrine sediment and soils. Removal techniques are sample dependent. Please consult the literature for the standard protocols for your samples. Here we generally use one of two techniques.

Supplies:

Preparing samples:

Samples must be dried, ground, and weighed prior to isotope analysis.

Following sample drying and grinding, samples need to be weighed into small tin (or in some cases silver) capsules prior to isotope analysis. Choose a capsule size appropriate for your sample weight.

For best results, samples should be weighted to &plusmin;1µg. Samples weighted to a lower precision can somewhat compromise the quality of %C, %N and C/N ratio data.

Weighing and crushing:
On a micorbalance tare an empty capusle and then add your sample. Once your sample is weighted, record the weight and shape the sample into a compact form for analysis.
For small samples (ca. <5 mg), use a pair of forceps to articulate and crush the capsule. Crush the samples such that the capsule is compact and roundish (low aspect ratio), does not have spurious edges, and does not have sample spilling out of it.
For large samples (ca. >5 mg), shape the sample into a cylinder using a homemade press. Make a press by drilling an approimately 5 mm hole in a 1/2" thick block of material (e.g., aluminum, or plastic), and making a piston of slightly smaller diamter (i.e., slightly less than 5 mm diameter).
Do not handle the casules with your hands because hand oils will contaminate your sample.

Sample Submission and Tray Preparation:

Shipping Info:

UCSC - Earth and Planetary Sciences
Stable Isotope Laboratory
1156 High Street, E&MS C512
Santa Cruz, CA 95064

Securing 96-well trays for shipping:

It is not uncommon for samples to be liberated from their well positions during transport or shipping. To ensure that samples remain in thier positions it is strongly recommended that a cover is placed over the sample wells before the lid is put in place. Covering the wells with parafilm, an index card, or aluminum foil, prior to securing the lid is advisable.