Technical Note: 40719 Biomedical sample analysis using the XSERIES 2 ICP-MS Introduction Key Words • Ari Mist Nebulizer • Biomedical Analysis • 3rd Generation CCTED • Xt Interface Trace element measurement in clinical samples is a challenging task. The complex sample matrices that need to be analyzed, such as serum and whole blood, together with the often low analyte concentrations present in these samples, both increase the difficulty of the measurements. Highly sensitive and robust instruments, capable of rapid and reliable analysis are required to accurately and precisely detect and quantify the analytes of interest, which has led biomedical analysts to invest in ICP-MS technology. The development in recent years of collision and reaction cell interference reduction technology for ICP-MS has provided an enhancement in data quality for key elements of biomedical interest that suffer from interference problems (for example 40Ar2+ on 80Se, 40Ar 35Cl+ on 75As+ and 40Ar12C+ on 52Cr+), thereby increasing the appeal of the technique to the biomedical community. This technical note describes the sample introduction apparatus and hardware features of the Thermo Scientific XSERIES 2 ICP-MS developed by Thermo Fisher Scientific to provide optimum performance for routine biomedical sample analysis. after dilution, less than 2 ml of sample is available. In these circumstances a low-flow nebulizer coupled with reduced sample uptake rates is required. In order to meet these requirements, a standard, robust sample introduction system for analysis of liquid biological specimens has been developed for the XSERIES 2 ICP-MS. This system incorporates the low-flow, blockage resistant Burgener Ari Mist nebulizer (Figure 1) and the highly matrix tolerant Xt interface (see XSERIES 2 ICP-MS Technical Note 40705) (Figure 2). Sample Introduction Requirements for Biomedical ICP-MS Analysis Several sample introduction characteristics are required to meet the demands of elemental analysis in biomedical samples. The elements of interest range from nmol/L levels of non-nutritional elements, such as Cd, in whole blood, through the µmol/L range, for Cu and Zn in serum, to mmol/L concentrations, for Na and K in all biomedical sample types, so a wide dynamic detection range is essential. The varying sample matrix composition, from blood, serum and urine, to hair, tissue, tooth and bone digests means that a robust sample introduction system, capable of handling these matrices without blocking or becoming unstable, is required. The complex sample composition also means that the interface cones of the ICP-MS must be sufficiently matrix tolerant to minimize the signal drift caused by sample deposition around the cone tips (particularly the skimmer cone tip). In addition to the sample matrix demands on the ICP-MS, occasionally the volume of sample provided for analysis may also be an issue. Since biological samples cannot be readily analyzed directly, because of their matrix ion concentration and viscosity, they normally require dilution (typically 10 or 20-fold) prior to analysis, which conveniently reduces the required amount of starting material required. However, there are cases when even Figure 1. The Burgener Ari Mist nebulizer Figure 2. The Xt interface. The Burgener Ari Mist nebulizer utilizes a parallel path design, in which the sample and nebulizer gas channels run alongside each other until meeting at the nebulizer tip. This design, which requires that samples be pumped through it (it does not free-aspirate, whereas concentric devices can), prevents particulates and other detritus in the sample blocking the nebulizer capillary or tip, a problem often encountered during biological sample analysis using standard concentric nebulizers. In addition, the parallel path design offers improved nebulization robustness and reproducibility with changes in sample matrix compared to concentric nebulizers. This offers particular performance improvements during urine analysis, where large variations in sample composition are frequently encountered. The Xt interface is composed of a Ni sample cone and exchangeable copper-cored Ni skimmer cone tip inserted into a metal adapter. The choice of adapter material, resulting from extensive investigations of different candidate metals, optimizes heat dissipation from the skimmer tip so that while the instrument is operating, the skimmer runs at a high enough temperature to prevent sample matrix from coalescing around the cone orifice. The result is enhanced stability and reduced signal drift during long term analysis of biological materials. The skimmer cone geometry matches that of the field-proven Xi interface, allowing the Xt interface to retain the benefits of this interface. These benefits, all of which are relevant for elemental analysis in biological samples, are: • Reduced polyatomic species and lower blank equivalent concentrations (BEC's) for easily ionized elements, such as Li, and cone derived ions, such as Ni Sampling and Sample Monitoring Requirements The varying and complex sample matrices that are introduced to the ICP-MS during biological analysis also mean that rapid washout is required to maximise sample throughput and minimise cross contamination from one sample to the next. The XSERIES 2 ICP-MS meets these requirements by offering several sample uptake and wash options with the combination of its versatile PlasmaLab™ software and the Cetac range of autosamplers (Figure 3). The options available include: • Fast uptake and wash, whereby the sample flow rate can be increased during the uptake and rinse cycles. This reduces analysis time, increases sample throughput and reduces analysis costs. • Monitored uptake / wash, where the uptake and wash times can be optimized sample-by-sample by intelligent monitoring of selected elements. This facility avoids carry-over problems from one sample to the next, by ensuring that the target signals have returned to baseline before the next measurement is started. It also ensures that sample uptake times are optimized, leading to increased productivity. • Autosampler probe-to-wash-early functionality, where the sample uptake probe can be sent to the wash after a predetermined time of taking up the sample. This allows the rinse cycle to start before the sample analysis has finished, thereby reducing rinse times to a minimum. It is a beneficial facility for analyses where only one or two, rapidly rinsed out analytes are required in a large number of samples (e.g. Pb in whole blood). Using this approach, sample throughput of > 50 samples per hour is achievable. • Low off-peak instrumental background of <0.5 cps, leading to industry leading detection limit capabilities for non-interfered isotopes • Attenuated signal at low masses, allowing major elements to be quantified together with minor and trace analytes in a single run without the need for further sample dilution Figure 3. XSERIES 2 ICP-MS and Cetac autosampler. Interferences in Biomedical ICP-MS Analysis Spectroscopic interferences in ICP-MS, arising from interaction of the sample matrix components and the plasma gas, have been extensively studied and characterized ever since the initial development of the technique in the early 1980's. For biomedical analysis, the most important spectroscopic interferences to be considered are given in Table 1 below. ISOTOPE Al V 35 C 40 Cr 40 Mn 40 Fe 40 Co 40 Ni 44 Cu 40 As 40 Se 38 Se 40 51 52 53 55 INTERFERENCE 12 14 27 56 59 60 63 75 78 80 Cd 111 C N1H+, 12C15N+ Cl16O+ Ar12C+, 36Ar16O+ and 35Cl16O1H+ Ar13C+, 36Ar16O1H+ and 37Cl16O+ Ar14N1H+, 40Ar15N+ and 54Fe1H+ Ar16O+ Ar18O1H+ and 40Ca18O1H+ Ca16O+ Ar23Na+ Ca16OH(H2O)+ Ar40Ar+ methane, oxygen or mixtures of these gases) inside the collision cell of the instrument. The target analyte ions undergo less interaction with the gas as they transit the cell and are detected, free of interference, downstream of it. The performance of the XSERIES 2 collision cell for the measurement of Se is illustrated by the calibration shown in Figure 4. With the XSERIES 2 ICP-MS the collision cell forms part of the standard ion focusing optics and as such can be easily switched on and off within a sample analysis to allow optimum data to be obtained for interfered and non-interfered analytes. All that is required is a short delay (typically 30 seconds) after switching the cell on or off to allow the ion beam to stabilize (further information about the XSERIES 2 ICP-MS collision cell technology can be found in the product note 40346_E). Using this technology, high accuracy results at low concentrations can be achieved for those elements of biomedical interest in biological specimens that are interfered in the absence of the cell (see Table 1). The performance of the collision cell for biological sample analysis is illustrated in the XSERIES 2 ICP-MS application notes AN_E0604 (Determination of Cu, Zn and Se in serum), AN_E0601 (Measurement of As and Cr in urine) and AN_E0649 (Trace element quantification in blood and serum in a single run). Ar40Ar+ and 79Br1H+ 94 Mo16O1H+, 95Mo16O+ Table 1. Interferences of most importance for biomedical analysis using ICP-MS In some cases, such as the 40Ar23Na+ interference on 63Cu, an alternative analyte isotope is available (65Cu, in this example). In others, mathematical interference correction, using another mass of the interfering species to determine the signal intensity of the parent interference, can be applied. For example, to correct for the 40Ar35Cl+ interference on 75As, the 40Ar37Cl+ signal at mass 77 (which itself must be corrected for 77Se) can be used. For interferences such as 40Ca16O+ on 60Ni, it is often effective to use empirically determined interference formation factors (i.e. formation rates) for the interfering species and then applying these correction factors in the software. Both these mathematical correction approaches are effective when the analyte signal is relatively large compared to the interference, but when the analyte signal is small with respect to the interference, mathematical corrections become less accurate. For this reason, an alternative approach is required to achieve accurate results at low analyte concentrations. This approach is the application of collision cell technology. 3rd Generation Collision Cell Interference Elimination Technology (CCTED) This technology, which has now been commercially available in ICP-MS instruments for more than 5 years, works by removing interferences through a combination of chemical and physical interaction of the ion beam with a collision gas (typically hydrogen, helium, ammonia, Figure 4. Se calibration using CCTED Conclusions With its standard liquid biomedical sample introduction system, versatile productivity-enhancing sample uptake/wash handling and advanced 3rd generation collision cell technology, the Thermo Scientific XSERIES 2 ICP-MS offers unrivalled performance for biomedical elemental analysis. The combination of the Burgener Ari Mist nebulizer and matrix tolerant Xt interface provides optimum robustness for routine, high throughout analysis of blood, urine and serum materials, following simple dilution of the samples. The high sensitivity and low background of the instrument yields exceptional detection limit capability, providing high quality data even at low analyte concentrations. These features, coupled with the effective interference elimination capabilities of the collision cell option, ensure that the XSERIES 2 ICP-MS is a powerful and effective tool for elemental analysis in biomedical analysis laboratories. Plasma Capabilities from Thermo Fisher Scientific In addition to these offices, Thermo Fisher Scientific maintains The use of an Inductively Coupled Plasma source (ICP) is the accepted and most powerful technique for the analysis and quantification of trace elements in both solid and liquid samples. Its applications range from routine environmental analyses to the materials industry, geological applications to clinical research and from the food industry to the semiconductor industry. Thermo Fisher Scientific is the only instrument manufacturer to offer the full range of Inductively Coupled Plasma Spectrometers (ICP, Quadrupole and Sector ICP-MS) to satisfy every aspect of plasma spectrometry from routine to highly demanding research applications. Develop your lab from the easy-to-use iCAP ICP to the high performance XSERIES 2 Quadrupole ICP-MS and up to the ultrasophisticated ELEMENT2 and NEPTUNE Sector ICP-MS instruments. 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