FacilitiesAnalytical InstrumentsThe UNH Stable Isotope Laboratory measures stable isotope ratios of carbon, nitrogen, hydrogen, and oxygen in environmental samples of solids, liquids and gases. Two isotope ratio mass spectrometers, both Finnigan Delta XPs, are the workhorses of the laboratory. These two machines with peripherals, allows for stable isotope analysis of carbon, nitrogen, oxygen, and hydrogen in solids, liquids, and gases. Click each link below for for detailed information.
DeltaPlus XP Mass SpectrometersThe University of New Hampshire Stable Isotope Lab has two Thermo Electron DeltaPlus XP isotope ratio mass spectrometers for measuring the stable isotopes of C, N, O, and H. The lab also houses 5 peripheral devices to introduce sample to the mass spectrometers. 
Mass Spectrometer 1The first DeltaPlus XP mass spectrometer is interfaced to a Costech ECS4010 Elemental Analyzer via a Conflo III and is dedicated to measuring 13C, 15N, C%, and N% of organic and inorganic samples. Samples are packed into small tin capsules and introduced into the Elemental Analyzer via a Costech Zero Blank Autosampler. Mass spectrometer 1 has a universal triple collector which allows for the measurement of C, N, and O stable isotopes. Additionally, we have outfitted the amplifier board on this mass spectrometer with two sets of gain resistors allowing us to measure a wider range of sample sizes. We can use a high amplification mode to measure C and N isotopes on samples containing as little as 5-10 ug of C or N. Mass Spectrometer 2
The second DeltaPlus XP mass spectrometer is interfaced to 4 different peripheral devices including a Thermo GC Trace Ultra, a Thermo TCEA via a Conflo III, a Thermo Gas Bench II, and a Thermo Precon device. Mass spectrometer 2 has a universal triple collector as well as two additional faraday cup collectors. The universal triple collector allows for the measurement of C, N, and O stable isotopes, while the two additional faraday cups permit measurement of H isotopes. The 4 attached peripherals are used to measure C, N, O, and H isotopes on a wide range of sample types including, inorganic and organic solid samples, water samples, trace gases, carbonates, compound specific molecules (including fatty acid methyl esters and amino acids), and more. |
Costech ECS4010 Elemental AnalyzerIn our lab the Costech ECS4010 Elemental Analyzer, or EA, is dedicated to measuring 13C, 15N, C%, and N% of organic and inorganic samples. Most often samples are in the form of a dried powder but we can handle some samples in liquid form (please speak with the lab manager).
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Thermo TCEA
The TCEA (or Temperature Conversion Elemental Analyzer) is used to measure 18O and 2H isotopes on solid organic and inorganic samples as well as on water samples. Since one of the goals of the TCEA is to measure oxygen isotopes, we cannot use an oxygen pulse (or oxygen containing catalysts such as tin) to combust the sample. Instead, the sample decomposes at relatively high temperatures (1350oC-1450oC) by pyrolysis. Organic and inorganic solid samples by TCEATo measure 18O and 2H isotopes on organic and inorganic solids, samples are ground to a fine powder and weighed into silver capsules prior to analysis. For 2H measurement, sample trays with encapsulated samples and standards are allowed to equilibrate with lab air for several days in order to correct for isotopic variations due to exchangeable hydrogen atoms in the sample. For oxygen analysis, however, we do not want adsorbed water to affect the 18O data so after equilibrating with lab air for several days, the sample is allowed to purge in a Zero Blank autosampler for several hours prior to analysis. When the analysis begins samples are dropped one at a time into a graphite crucible located in a glassy carbon reactor held at high temperature (1350oC -1450oC depending on the application). The strongly reducing environment and excess of elemental carbon in the reactor ensures that all oxygen in the sample is converted to CO and that all hydrogen is converted to H2. The gases then pass through a water trap and through a (how long) packed molecular sieve GC column to separate H2 from CO, as well as these two gases from any other gases produced during pyrolysis (such as N2). Precision? Water samples by TCEAFor water samples the theory of operation is basically the same but sample preparation is different. Water samples are placed in vials and closed to the atmospheric with septum caps. A GC PAL autosampler injects 0.5 ul of liquid into the top of the glassy carbon reactor (held at 1400oC) where conversion to H2 and CO takes place. Again a water trap dries out the produced gases and a GC column separates them from one another before detection by the mass spectrometer. Link to the price of different types of analyses we can do (organic solid, 15N of NH4 and NO3 in soils). Precision? |
Thermo Trace GC Ultra
The gas chromatograph (GC) in our lab is mainly used for compound specific isotope analysis on liquid or gaseous samples. For example, instead of measuring bulk fish tissue, more information can be obtained by measuring isotopes of individual amino acids or fatty acids in that fish tissue. Compound specific analyses require some preparative chemistry prior to analysis (speak with the lab manager about this). We have the ability to measure 13C, 15N, 2H, and 18O isotopes on compound specific analytes. 13C and 15N analysis on the Trace GC UltraFor 13C and 15N analysis on the Trace GC Ultra, the concept is similar to that of the elemental analyzer in that we will be measuring these isotopes on CO2 and N2 gas. The big difference is that the GC column on the Trace GC Ultra is usually much more complex than the 3 meter column on the elemental analyzer. We have several different columns available to use on the Trace GC Ultra with a variety of active phases, polarities, and lengths (up to 60 meters long). For 13C and 15N analysis on the Trace GC Ultra, samples are injected using an AS2000 autosampler into a heated inlet where the sample is vaporized (note that the sample has to be prepared in such a way that it is volatile at the inlet temperatures, 250-280oC). The vaporized sampled does not immediately undergo combustion as in the EA but instead passes through the GC column. Once the compound specific analytes are separated and elute from the column they pass through combustion and reduction reactors where they are individually combusted and reduced to yield CO2 and N2 gases. A water trap dries out the gas stream before it enters the mass spectrometer for isotope detection via an open split. The mass spectrometer can only measure isotope ratios of carbon and nitrogen on CO2 and N2. The mass spectrometer cannot not recognize for instance, one amino acid from another, or measure isotope ratios on amino acids. That is why efficient analyte separation on a GC column followed by combustion and reduction is crucial for compound specific isotope analyses. 2H and 18O analysis on the Trace GC UltraFor 2H and 18O analysis on the Trace GC Ultra, the concept is the similar to 13C and 15N analysis on the Trace GC. Again it is necessary to volatilize the compounds or analytes of interest and then separate them on a GC column. Once the compounds are separated they individually pass through a pyrolysis reactor where hydrogen and oxygen in the sample are converted to H2 and CO (similar to the TCEA). The gas stream in dried in a water trap and then enters the mass spectrometer through an open split. |
Thermo GasBench II
Information coming soon... |
Thermo Precon Device
Information coming soon... |
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Solid samples that are ground to a fine powder are weighed to the thousandth of a milligram, tightly packed into small tin capsules, and stored in a dessicator prior to analysis. Samples are then placed into a Zero Blank autosampler where atmospheric gases containing C and N are purged by ultra high purity He carrier gas. Once the autosampler has been purged it is closed to the atmosphere and analysis begins.