temperature to achieve improved sensitivity and accuracy, especially for the analysis of precious metals. Figure 6. Effect of IsoMist XR Temperature on Measurement Accuracy - Pt 214 - Pt 265 - Pt Gravimetric Value Another advantage of utilizing the IsoMist XR at an elevated temperature is when samples are very limited in volume. We have shown in two separate studies2,5 that samples can be analyzed at very low uptake rates with a heated spray chamber without the ensuing loss in detection limits as would be realized on a conventional spray chamber without temperature control. (Heating the spray chamber for higher uptake rates may result in overloading the plasma.) Heating the spray chamber can also improve the analysis of viscous samples such as lubricants and edible oils, which would otherwise solidify at room temperature. Improved Detection Limits An investigation was recently carried out using the IsoMist XR connected to a Spectro Arcos II MV ICP-OES at a NY water treatment facility. After optimizing the nebulizer and ICP operating conditions, the IsoMist XR was used to finely tune the conditions for optimal signal intensity and reduced background. Replacing the standard cyclonic spray chamber with the IsoMist and optimizing the sample introduction environment at 5°C provided a significant improvement in instrument detection limits (Table 1). In contrast to the precious metal study, a lower temperature with the water samples improved detection limits by reducing background and yielding a more robust and higher temperature plasma. Improved Washout Previous work6 highlighted the advantage of the Helix zero dead volume nebulizer interface by comparing the time required to washout a 10ppm Molybdenum standard with the Helix interface and a “Brand-X” spray chamber with an o-ring interface. The results showed the 10ppm standard washed out in 4 seconds with the Helix interface, compared to 16 seconds with “Brand-X” (Figure 7). Application Spotlight compared to previous work1,2,7,8 at -10°C resulted in better precision and accuracy and higher intensities (Figure 4). The extended temperature range of -25°C makes the IsoMist XR the perfect tool for analyzing volatile solvents like naphtha and gasoline without dilution. Figure 6: Effect of Spray Chamber Temperature on Intensity Figure 4. Effect of IsoMist XR Temperature on Signal Intensity in Naphtha 120 100 80 60 40 20 0 Cd2144 Ca3158 Ag3280 B_2088 Ba2335 Ba2347 Cr2055 Cu2477 -25oC -10oC K_7664 Mg2790 Mn2939 Mo2816 Fe2611 P_1859 Pb2203 Ni2303 Si2516 Sn2839 V_2687 Ti3349 Zn3302 Enhanced Sensitivity and Accuracy The sensitivity for many analyses can be enhanced by operating the spray chamber at elevated temperatures. In a previous study4, the IsoMist XR was used in combination with an Agilent (Varian) Vista Radial ICP-OES instrument to investigate the effect of spray chamber temperature on precious metal signal intensity and analytical accuracy. The elements analyzed included: gold (Au); iridium (Ir); palladium (Pd); platinum (Pt); rhodium (Rh); and ruthenium (Ru). Figure 5 shows the average signal intensity of these precious metals increasing relative to an increase in IsoMist XR temperature. Figure 5. Effect of IsoMist XR Temperature on Signal Intensity for Precious Metals To evaluate the effect of IsoMist XR temperature on the accuracy of precious metal measurements, a solution of Pt was analyzed at a range of temperatures and compared to the Pt concentration determined gravimetrically.4 The results show the Pt concentration is closer to the gravimetric or true value at a temperature of 40 °C (Figure 6). The results from both experiments clearly highlight the advantage of utilizing the IsoMist XR at a higher spray chamber www.geicp.com Glass Expansion Newsletter | Issue 42 3
GE Newsletter February 2017
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