Analytical Techniques/Capabilities |
Analytical Techniques/Capabilities |
The ND ICP-MS lab is composed of two instruments, the VG Fisons PlasmaQuad II Quadrupole ICP-MS (PQII) and the Thermo Finnigan Element 2 High-Resolution Double Focusing Magnetic Sector ICP-MS (Element 2). With the addition of the Element 2 to our lab in March of 2004, our PQII is now devoted to student teaching and to trace element analyses where low detection limits are not necessary. The Element 2 has replaced the PQII as the workhorse of the lab and offers lower detection limits, increased sensitivity, and high-resolution capabilities that cannot be achieved by the PQII. In addition, we have a 213 nm ND-YAG New Wave Research Laser Ablation system and a Dionex HPLC front-ends that greatly expand the capabilities of the Element 2.
See our publication page for references.
UPDATE: The PQII is currently down. A timeframe for repair will be posted as soon as possible.
The PQII was purchased and installed in 1992. The instrument was the workhorse of the lab until the purchase and installation of the Element 2 in 2004. The PQII is a versatile machine capable of handling a diverse range of sample types and concentration ranges. Geological, biological, and chemical samples are handled with ease. The working concentration range is ppm to sub-ppb (with ultrasonically nebulized sample introduction). The PQII is now devoted exclusively to aqueous analysis as all laser ablation work is now performed on the Element 2.
The age of the PQII predates the extensive use of computer control on all aspects of the operation of the machine; therefore, turning of the PQII requires careful manipulation of the lens stack voltage and gas flows via control knobs on the machine itself. This is in stark contrast to new ICPM-MS instruments (including our Element 2) where nearly all aspects of usage is done via computer. This makes the PQII an excellent learning machine as students get more of a "hands-on" approach to using a mass spectrometer.
The PQII is a quadrupole ICP-MS, meaning that mass differentiation is performed by four cylindrical or hyperbolic rods. One pair of rods are positively charged and the other negatively. The resulting field segregates the passing ions on the basis of the mass to charge ratio (or m/z). Applying a different rf/dc voltage to the quadrupole changes which m/z ratio (or, in effect, which mass, since the plasma (theoretically) ionizes every element to a +1 charge) is allowed to pass. Resolution is on the order of approximately 400 (~ 1 AMU) using the 5% height method. The quadrupole can scan at the rate of approximately 2500 amu/second, meaning that rapid scans of the entire mass range from Li 7 to U 238 can be done quickly and with great precision.
The Element 2 is an advanced double focusing magnetic sector ICP-MS capable of significantly decreased detection limits and higher sensitivity and resolution compared to the PQII. The Element 2 has three resolution modes: low (resolution = 300), medium (resolution = 4,000), and high (resolution = 10,000). Medium and high resolution modes provide separation of the analyte signal from spectral interferences, making accurate and precise elemental analysis of trace element in complex matrices possible without complicated and time-consuming sample preparation.
The ion beam passes through a strong magnetic field generated by a large magnet. The magnetic field is dispersive with respect to ion energy and mass. The second focusing occurs at the electro-static analyzer or ESA. The ESA is dispersive with respect to ion energy and focuses the ion beam through the exit slit to the detector. Please see this link for a Quicktime movie illustrating the flight of the ion beam through the magnet and ESA.
| Specifications | |
| Sensitivity: | > 1 x 109 cps/ppm In |
| Detection Limits: | < 1 ppq (non-interfered) |
| Dark Noise: | < 0.2 cps |
| Dynamic Range: | > 109 linear |
