Ferritor Hall 116
1 University of Arkansas
Fayetteville AR 72701
P: (479) 575-2543
F: (479) 575-4010
The dual-inlet consists of two gas bellows connected by a change-over valve to the mass spectrometer. The sample is introduced manually into one bellows, and standard gas is in the second bellow. Eight to ten alternate measurements are taken of the sample and standard. This results in a very precise measurement (precision better than 0.01 ) of the sample isotope composition. The disadvantage of the dual inlet is that it requires extensive off-line preparation to produce pure gas for the analysis. Our mass spectrometer has a multi-port system that allows for the automated analysis of ten samples.
n continuous flow analysis the sample is introduced into a Helium stream from one of several peripheral devices. A capillary takes a sample of the Helium stream and introduces it into the mass spectrometer. Our three IRMS systems use continuous flow. One system has a GC connected via a GC interface to a Delta Plus mass spectrometer. The other system has an Elemental Analyzer connected by a Conflo II and a Preconcentrator connected by a GP interface to a Delta Plus mass spectrometer. The third system has a high temperature elemental analyzer (TC/EA) connected via a Conflo III and a Gas Bench II. The TC/EA and Gas Bench use a CTC Analytics GC-Pal autosampler.
The elemental analyzer is for routine analysis of organic samples for δ15/14N, δ13/12C, %N, and %C. A sample is combusted in an Oxygen stream at 1100C,then passed through oxidation and reduction tubes to form CO2 and N2 gas. The peaks are separated on a chromatography column allowing both C and N isotope composition to be determined on a single sample. The precision is better than 0.2 for C and 0.4 for N. The disadvantage of the elemental analyzer is that it is not as precise as the dual inlet. The advantages are that sample prep is much easier, many more samples can be analyzed per day, and δ15/14N, δ13/12C, %N, and %C are measured on each sample.
The TC/EA is designed for the determination of δ18O and HD in water and organic samples. The sample is combusted at very high temperatures (1300C) in a reducing environment. This converts oxygen to CO. The precision is better than 0.4 for δ18O.A Costech Zero Blank Autosampler is used with the TC/EA.
The Gas Bench II is an online interface which automates the isotope ratio determination of smaller gas samples allowing for the analysis of δ15/14N and δ18/16O from nitrates.
The GC-IRMS allows us to look at isotope values of individual compounds such as fatty acid and amino acids.
The Agilent GC/MS is for the identification and quantification of compounds for compound-specific analysis.
The Sartorius SC-2 Microbalance is a highly accurate balance with a draft shield coupled to a laptop allowing the balance to send the sample weight directly to an electronic spreadsheet for accurate and consistent measurements.