Equipment

Inductively Coupled Plasma Mass Spectrometer (ICP-MS) is an analytical technique used for elemental determinations. We are equipped with a Thermo Scientific ELEMENT 2, a high performance, double focusing magnetic sector field ICP-MS.

Aerosol samples are transported into the core of the inductively coupled argon plasma which generates temperatures of 600-10000 degrees C, where they are completely desolvated and ionized. The resultant ions are separated and collected by mass to charge ratios. The multi-elemental detector has the speed to handle transient signals such as those from laser ablation. It can measure elements across the periodic table from mg/L to sub pg/L concentration ranges.

We are equipped to run solution and laser ablation analyses. Our laser is a 193 nm Excimer laser from Photon-Machines for the ablation of any type of solid sample with no sample preparation procedures.

This is primarily used for the determination of anions and cations in waters, such as nitrate, chloride, bromide etc.

The department’s SEM has several imaging and operation modes. Realistic zoom range is from 50x to 50,000x or mm scale to µm scale objects. This varies with the type of sample and mode of operation.

With the exception of "Low Vacuum Mode" below, samples need to be electrically conductive or coated in a conductive coating. The department has both a carbon coater and a gold/palladium sputter coater. All imaging modes takes place in a high or low vacuum which could damage some delicate samples.

EDS, also known as Energy Dispersive X-ray Analysis (EDX) is a qualitative or semi-quantitative elemental analysis method. The flatter the surface being analyzed, the better the results. The system can obtain elemental spectrum from the entire field of view, spots, selected areas, lines or create maps of elements. It can also create phase maps of similar spectrum.

XRD uses an x-ray source directed at a crystalline sample which diffracts the x-rays. This diffraction pattern is unique for specific materials and by comparing it to a library of known materials the unknown can be determined. Our diffraction library only includes natural minerals.

Samples are run as a homogenous powder. The most accurate results a generated when the sample particles are the same size and randomly oriented in the sample holder. The sample holders have a depression that is filled with the sample powder. About 1mg of sample is ideal but less will still produce a clean diffraction pattern if run for a longer time.

XRF uses an x-ray source to excite a sample and measure the secondary x-rays emitted to determine and measure the elements present. It can give elemental concentrations of solids, powders, films and liquids.

Two Isotope Ratio Mass Spectrometers are used in the NIU Stable Isotope Laboratory (SIL), Thermo Fisher Scientific MAT 253 and Delta Plus Advantage. Samples can be analyzed directly in a dual inlet mode (e.g. CO2, O2, N2 gas) or after conversion to these simple gases using various online techniques.

Our laboratory is equipped with Elemental Analyzer (EA, Costech ECS 4010) that converts samples designated for carbon 13C/12C and nitrogen 15N/14N isotope analyzes to CO2 and N2 (Thermo-Finnigan DELTAplus Advantage). Samples frequently analyzed using EA include plant material, animal tissues, soil. In addition to the EA, a Gas Chromatograph (GC) is coupled to the same IRMS via a combustion interface (Thermo Fisher Scientific GC-C III), which allows us to analyze the stable carbon (13C/12C) or hydrogen (2H/1H) isotopes of a single organic compound.

To analyze hydrogen and oxygen stable isotopes in organic samples (e.g. cellulose) or inorganic, for example water, Thermal Conversion/Elemental Analysis (Thermo Finnigan TC/EA) is used. Sample is converted to H2 and CO using pyrolysis reactor and directed to the IRMS for measurements (2H/1H, 18O/16O).

Another sample preparation peripheral that is used online is the Gas Bench (Thermo Fisher Scientific), which is used to analyze carbonates, dissolved inorganic carbon or water for their isotope ratios of oxygen and/or carbon (18O/16O and 13C/12C). To analyze oxygen and silicon isotopes (18O/16O and 29Si/28Si, 30Si/28Si ) in quartz samples we first liberate oxygen as O2 and convert Si to SiF4 with the use of a fluorination reaction and a laser (Photon Machines Fusion 10.6 Laser) before transferring the gasses to IRMS (Thermo Fisher Scientific MAT 253).