Overview

We analyze solid carbonate samples for the stable isotope ratios of δ13C and δ18O using a Thermo Gas Bench coupled to a Delta V IRMS with a GC Pal auto-sampler. Typical samples include modern or fossil bioapatites (bone and teeth) and foraminifera. Weighed samples are transferred to exetainers, purged of atmosphere with helium and acidified with phosphoric acid to convert solid carbonates to CO2 gas. The target gas is concentrated as a frozen solid within a loop submerged in a liquid nitrogen bath. The gas is then released back into the helium carrier gas to the IRMS upon removal of the loop from the nitrogen bath.

Sample Preparation

Minimum weight needed for most sample material for carbonate analysis is 1 to 2 milligrams. If your available sample amount is an issue, our high-sensitivity “Precon” may be an option for smaller amounts. Please contact us ahead of time if this case. Samples need to be dried thoroughly before weighing and analysis.

Price List

Overview of technique

Micro-Dumas combustion analysis for total carbon, total nitrogen and sulfur in solid-phase samples is based on transformation to gas phase by extremely rapid and complete flash combustion of the sample material. We can analyze most ecological sample types (animal and plant tissue, soils, sediments, etc.) for carbon and nitrogen content and are currently limited to organic samples (e.g. animal and plant tissue) for sulfur analysis.

Sample prep considerations

Plant samples must be oven-dried, ball-milled to less than 250 um particle size and weighed (~3 mg, with ug digits significant) into 5 x 5 mm tin capsules before combustion. Poor precision can often be traced to inadequate grinding that leaves fibrous matter or visible granules in the sample. Clients may send us unprocessed samples (e.g. litterbag contents) or may provide any of the above processing themselves at a major reduction in price.

Price List

Method Summary

Isotope-ratio analysis for nitrogen-15N, carbon-13C and sulfur-34S in solid-phase samples starts with transformation to gas phase by extremely rapid and complete flash combustion of the sample material. Ionized combustion product is mass-analyzed by means of differing mass/charge ratios among the various isotopic species of N2, CO2 and SO4. We can analyze most ecological sample types (animal and plant tissue, soils, sediments, etc.) for carbon and nitrogen and are currently limited to organic samples (e.g. animal and plant tissue) for sulfur analysis.

Sample prep considerations

Solid samples must be oven-dried, ball-milled to less than 250 um particle size and weighed (~3 mg, with ug digits significant) into 5 x 5 mm tin capsules before combustion. Poor precision can often be traced to inadequate grinding that leaves fibrous matter or visible granules in the sample. Clients may send us unprocessed samples or may provide any of the above processing themselves at a major reduction in price.

Price List

Overview of the 15N diffusion method

We use the ammonia diffusion method to extract natural-abundance nitrogen for isotopic characterization. The process involves increasing the pH of the dissolved sample, converting the ammonium to gaseous ammonia, which is captured on an acidified filter in the headspace (Holmes et al. 1998). Nitrate-specific 15N is quantified by first boiling-off the volatile ammonia, adding a reducing agent to convert oxidized N to NH4, then proceeding with the standard diffusion and ammonia capture on an acidified filter (Sigman et al. 1997). The filter is then analyzed as a typical solid sample on our Carlo Erba IRMS.

Sample collection and preparation for 15N diffusion

Estimate the minimum expected concentration of the target N-forms. Calculate the volume of sample needed to contain at least 10µg of target N. Collect at least this volume for each N-analyte. If samples need to be stored before shipping, filter with Pall A/E or Whatman GF/F grade glass fiber filters and freeze. Ship samples over night with adequate dry ice to keep frozen for 36 hours.

References

Sigman, D. M., M. A. Altabet, R. Michener, D. C. McCorkle, B. Fry, and R. M. Holmes. 1997. Natural abundance-level measurement of nitrogen isotopic composition of oceanic nitrate: an adaptation of the ammonia diffusion method. Marine Chemistry 57:227-242.

Holmes, R. M., J. W. McClelland, D. M. Sigman, B. Fry, and B. J. Peterson. 1998. Measuring 15N-NH4 in marine, estuarine and fresh waters: an adaption of the ammonium diffusion method for samples with low ammonium concentrations. Marine Chemistry 60:235-243.

Price List

Overview

We use an OI-Analytical Aurora 1030W TOC analyzer coupled to a Thermo Delta V to analyze dissolved organic and inorganic 13C. Dissolved inorganic carbon-13C is determined by measuring the CO2 released following the addition of hydrochloric acid. Using the heated persulfate wet oxidation method, dissolved carbon is completely oxidized and analyzed as CO2 in the IRMS.

Sample preparation

We recommend supplying at least 30 mL of filtered sample on 40 mL amber glass bottles. Refrigerate samples until analysis. If samples are to be shipped, individually wrap each glass sample bottles with bubble wrap or comparable packing material and use water tight bags (such as Ziplocks) for secondary containment. Ship on ice packs.

Price List