Application Spotlight Introduction The IsoMist, first introduced by Glass Expansion in 2007,1 provided ICP laboratories with a convenient self-contained alternative to a jacketed spray chamber by eliminating the need for a bulky chiller, liquid coolant, complex coolant tubing and the icing-up of the spray chamber. In contrast to the limited temperature range of a jacketed spray chamber, the IsoMist provided a programmable range of -10°C to +60°C in increments of 1°C. This temperature flexibility addressed the challenges associated with several ICP applications.1-12 The IsoMist XR incorporates an improved thermodynamic design, providing an extended temperature range and faster equilibration so that your target temperature is attained more quickly. The spray chamber temperature of the IsoMist XR is accurately controlled using a multi-stage Peltier device, with a range of -25°C to +80°C in increments of 1°C. The proprietary software of the IsoMist XR is connected via a USB port or wireless Bluetooth® technology. A cyclonic spray chamber encapsulated with a temperature conductive resin provides the IsoMist XR with a uniform spray chamber temperature from top to bottom and an air tight fit within the module.5,6 These features allow for a stable temperature to be maintained with an unmatched accuracy of +/- 0.1°C and prevent condensation build-up and freezing. The combination of the encapsulated spray chamber and dual-stage Peltier allows the IsoMist XR to reach -25°C in less than 15 minutes (from ambient temperature). The IsoMist XR is compatible with interchangeable glass, quartz and PFA cyclonic spray chambers, offering the analyst the utmost flexibility and optimum setup for any matrix. Glass Expansion’s proprietary HelixTM o-ring free nebulizer interface eliminates sample contamination and ensures easy nebulizer removal. This zero dead volume nebulizer interface reduces carry-over, improves washout between samples5 and a built-in positive stop ensures optimum and reproducible nebulizer insertion depth for consistent nebulizer performance. Results In order to achieve optimum ICP performance in each of the applications described, it is important to note that in addition to using the IsoMist XR, a proper nebulizer and optimum ICP operating conditions were selected to best handle the particular sample matrix studied. This is essential when dealing with a challenging sample matrix. Improved Stability Fluctuations in laboratory temperature affect sample viscosity and nebulization efficiency. Previous investigations showed a change of 1°C in spray chamber temperature can result in a sensitivity change of 3%6 Figure 2 compares the long term signal intensity achieved with the IsoMist XR held at a constant temperature compared to a conventional cyclonic spray chamber. The results show that maintaining a constant temperature with the IsoMist XR significantly enhances long term stability of the ICP signal intensity, resulting in improved analytical reproducibility and accuracy. Maintaining a stable ICP signal with the IsoMist XR also enhances throughput and lowers operating costs by reducing the need to re-run samples should a QC check drift outside the acceptable range. Figure 2. Effect of IsoMist XR on signal stability at ambient temperature With IsoMist XR at constant 21oC Standard System Normalised Counts 0 1.04 1.02 1.00 0.98 0.96 0.94 0.92 Al Cr Cu Mn Ni Zn 50 100 150 200 Time (minutes) Reduced Oxide Interferences Using the IsoMist XR spray chamber at sub-ambient temperatures on an ICP-MS reduces the water vapor transferred to the plasma resulting in lower oxide formation and reduced polyatomic (ArO, ArOH) interferences. Figure 3 shows the effect of IsoMist XR temperature on the ICP-MS oxide ratio obtained on a PerkinElmer Elan ICP-MS. A reduced temperature between 1 and 4°C provides the optimum oxide ratio. Lowering oxide formation in the plasma translates to fewer interferences, improving accuracy and detection limits.1 Figure 3. Effect of IsoMist XR Temperature on ICP-MS Oxide Ratio CeO/Ce % -5 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0 5 10 15 20 25 Volatile Solvents Temperature ºC Volatile organic solvents are a challenge due to high transport efficiency to the plasma, creating an excessive load resulting in plasma instability or, in the worst case, cessation. One of the most difficult and commonly analyzed solvents is light naphtha. Due to its high volatility, naphtha is usually diluted with a less volatile solvent, like kerosene. However, a dilution restricts lower detection limits from being achieved. The IsoMist XR was used in combination with a Thermo iCAP 6500 Duo ICP-OES for the direct analysis of naphtha, without dilution12 Setting an IsoMist XR temperature of -25°C, www.geicp.com Glass Expansion Newsletter | Issue 42 2
GE Newsletter February 2017
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