Facility

The Stable Isotope Mass Spectrometry (SIMS) lab in the Department of Soil Science is housed in Williams Hall on the main campus of North Carolina State University. This facility aids investigators in their research by utilizing the latest advances in Continuous Flow Isotope ratio Mass Spectrometry (CF-IRMS). A variety of sample types can be analyzed for δ¹⁵N, δ¹³C, total %N, and total %C. The SIMS facility accepts both natural abundance and isotopically enriched samples for analysis.

Instrumentation

A Thermo Finnigan DELTA plus mass spectrometer is used to measure the ¹⁵N/¹⁴N and ¹³C/¹²C ratios of gases. Solid samples are introduced into the system using a CE Elantech NA 2500 elemental analyzer. Dried, well-homogenized samples are weighed and placed into small tin capsules. These are then loaded into an autosampler, which drops them into a combustion oven. They are combusted at over 1000 ° C and converted to their base elements in the gas state. The resulting gases are then passed through reaction columns and traps until only CO₂ and N₂ remain. These gases are separated on an analytical column and then passed on to the mass spectrometer via a Conflo II open split interface. Here the gases are ionized and the resulting signals for each isotope recorded by the computer based data system. Results for both isotope and percent composition data can be obtained in one run for most samples.

Sample Types

A wide range of sample types can be analyzed on the system, including:

• soils
• plant tissue and extracts
• animal tissue
• water
• finished food products

There are many different ways that samples can be prepared for analysis, but in the end they must all meet the same requirements: they must be dry and very homogenous. Only a small amount of sample is necessary for analysis, since the system is capable of detecting microgram quantities of CO₂ and N₂. Based on the amount of carbon and nitrogen in a sample, the final sample size may range anywhere from a few hundred micrograms to several milligrams.

Examples of Stable Isotope Applications

• Detection of adulterated food products
• Tracing of groundwater and soil pollutants
• Nitrogen nutrition in plants
• Denitrification
• Nitrogen fixation
• Animal metabolism
• Ecosystem studies

Pricing

The cost of analysis includes experiment design consultation, method development, and customized results reporting. Please feel free to call, email, or stop by the lab to discuss your particular analytical needs.