High resolution mode

Figure 9. Schematic diagram showing a second-generation MC-ICPMS instrament (ThermoFinnigan Neptune). This instrument utilizes double-focusing and is equipped with a motorized multiple-Faraday collector block with two channels that can be operated in high-resolution mode. Optional multiple-ion counting channels are also available for the simultaneous measurement of low-intensity ion beams. [Used with permission of Thermo Finnigan.]...

The reason is truncation of dynamics in low-resolution modes in a 14-bit-detector each pixel in low-resolution mode can contain 0 to 16382 counts. With the next photon an arithmetic overflow will occur and the pixel is saturated. In high-resolution mode the same area of the detector is represented by 4 pixels, and if the intensity is evenly distributed it takes 4 times longer before the pixels will be saturated. If the high resolution is not required and the cycle time is 30 s or longer, it is good practice to store away the big files on a spacious USB hard-disk and afterwards to bin the data. 

In the broadband (low mass resolution) mode the only ion detected was the [M+H]+ ion, and in the narrowband mode a mass resolution of ca. 90,000 (resolution specified at FWHM) was obtained. Note also that the signal-to-noise ratio in the broadband mode is > 100 1 for a sample size of 100 pmol, and in the narrowband (high resolution) mode the signal-to-noise ratio is greater than 500 1. Owing to the pulsed ionization used for FTMS, the total ionization time required to produce this spectrum was approximately 80 ms. That is, the Cs+ ion beam was turned on for 4 ms to produce each mass spectrum and 20 individual ionization events were signal-averaged. 

When a high resolution mode is required, first switches 22 are closed so as to ground the enclosure regions 13 and second switches 23 are opened so as to float gate electrodes 15. Carriers generated in the vicinity of the enclosure regions are attracted and absorbed by the junction potential of the enclosure regions. Thus, no carriers flow into adjacent photodiodes. 

Particularly for low-mass analytes, sector-based mass spectrometers used in a high-resolution mode can reduce spectral overlaps due to polyatomic ions, thereby improving detection limits compared to those of quadrupole mass spectrometers. However, ion transmission efficiency decreases significantly as the resolution is increased. For example, increasing the resolution provided by the sector mass spectrometer from 300 to 3000 reduces the ion transmission efficiency by about a factor of 14 [127], Further increasing the resolution to 7500 results in another order of magnitude loss in ion transmission efficiency [127]. The use of reaction cells may provide an alternative or complementary means to reduce background due to polyatomic ions. 

Semiquantitative analysis procedures have also been used with laser ablation ICP-MS [71,210-213]. The effect of experimental parameters and potential improvements in accuracy of semiquantitiative analysis using ICP-MS have also been discussed recently [208,214-216], along with the use of semiquantitative analysis with a double-focusing ICP-MS in both low- and high-resolution modes [217]. 

HPLC-SFMS (low and high resolution mode)82Se identiP-cation of species based on their chromatographic properties and the results of standard addition... 

Another possible evidence of grafted organic/polymeric molecules onto CNT surface can be achieved by microscopy analyses using both principal types of electron microscopy - transition electron microscopy, TEM, or scanning electron microscopy, SEM (15,19,24,44,45,47). Such analyses are usually performed after careful extraction of the polymer from tubes by polymer solvents, performed several times by a reflux procedure with an excess of solvent therefore it is supposed that only covalently attached molecules remain fixed at CNT surface. High Resolution mode of TEM analysis shows the evidence of amorphous material on nanotubes surface (15). 

IRS Infrared Spectrograph, the spectrograph on board the Spitzer Space Telescope. The instrument had a low- and high-resolution mode, providing sensitive spectra from 5 to 40 pm. 

X-ray photoelectron spectroscopy (XPS) was used to analyze polymer surfaces before and after ion beam irradiation. Data were collected with a Surface Science SSX-100 spectrometer using A1 Ka x-rays in the high resolution mode with x-rays focused to a spot size... 

Profiling should be conducted in high resolution mode in order to precisely determine mass and verify precursor isotopic distributions of M + 1 and M + 2 isotopic patterns where appropriate. Excessively high standard concentrations will interfere with isotopic distribution verification and accurate mass determination if the signal for the molecular ion is saturated. Once the precursor and... 

AT Townsend. The determination of arsenic and selenium in standard reference materials using sector field ICP-MS in high resolution mode. Fresenius J Anal Chem 364 521-526, 1999. 

Apart from high resolution mode, which is not able to eliminate all those interferences, further possibihties to overcome these interferences are mathematical correction procedures, which can be applied to rectify results, but they have to be specifically modeled for each sample matrix (Krachler et al. 1998 Barbante et al. 2001 Carol et al. 2001) and are prone to errors due to the relatively high abundance of interferents. By employing membrane desolvation for the reduction of oxide formation, spectral interferences can be significantiy reduced, but in case of road dust mathematical correction stiU had to be applied to compensate for Sr interference (KoUensberger et al. 2000). To further minimize the risk of interferences, pretreatment routines have to be employed, entaihng additional risks of analyte losses. 

Version 2 will in addition support EGA in high resolution mode and Hercules graphics. 

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