ICPMS

A novel interface to connect a ce system with an inductively coupled plasma mass spectrometric (icpms) detector has been developed (88). The interface was built using a direct injection nebulizer (din) system. The ce/din/icpms system was evaluated using samples containing selected alkah, alkaline earths, and heavy-metal ions, as well as selenium (Se(IV) and Se(VI)), and various inorganic and organic arsenic species. The preliminary results show that the system can be used to determine metal species at ppt to ppb level. 

Laboratoire de Chimie Physique et Microbiologie pour VEnvironnement, Unite Mixte de Recherche UMR 7564, CNRS - Universite H. Poincare Nancy I, 405, rue de Vandoeuvre, F-54600 Villers-les-Nancy, France E-mail walcarius Icpme. cnrs-nancy.fr... 

Figure 4 Measurements of (A) uranium aetivity ratios, UARs ( U U) and U eoneentrations (B) aeross a salinity gradient off the Amazon River mouth (1996). UARs were determined by thermal ionization mass speetrometry (TIMS) at Calteeh (D. Poreelli) U eoneentrations by ICPMS...

Inductively Coupled Plasma Mass Spectrometry, ICPMS... 

Inductively Coupled Plasma-Optical (ICP-optical) methods and ICPMS are extremely sensitive elemental survey techniques that also are described in this volume. ICP methods, however, require a solution for analysis, so that the direct... 

ICPMS can be considered a high-sensitivity extension of mass spectrometry, as well as an increased-sensitivity detector replacing optical ICP (ICP-OES) analysis. In fret, both viewpoints are accurate, and the wide application of ICPMS analysis... 

All of these components are critical to the high sensitivity found in ICPMS instruments. Figure 1 shows their arrangement. 

The mass spectrometer usually found on ICPMS instruments is a quadrupole mass spectrometer. This gives high throughput of ions and resolutions of 1 amu. Only a... 

The inductively coupled plasma and the torch used in ICPMS are similar to that used in ICP-OES. In ICPMS, the torch is aimed horizontally at the mass spectrometer, rather than vertically, as in ICP-OES. In ICPMS the ions must be transported physically into the mass spectrometer for analysis, while in ICP-OES light is trans-... 

The part that marries the plasma to the mass spectrometer in ICPMS is the interfacial region. This is where the 6000° C argon plasma couples to the mass spectrometer. The interface must transport ions from the atmospheric pressure of the plasma to the 10 bar pressures within the mass spectrometer. This is accomplished using an expansion chamber with an intermediate pressure. The expansion chamber consists of two cones, a sample cone upon which the plasma flame impinges and a skimmer cone. The region between these is continuously pumped. 

By for the most simple acid to work with in ICPMS is nitric acid. This has minimal spectral interferences and in concentradons under 5% does not cause excessive wear to the sample cones. Other acids cause some spectral interferences that often must be minimized by dilution or removal. When HF is used, a resistant sampling system must be installed that does not contain quartz. 

The role of the nebulizer in ICPMS is to transform the liquid sample into an aerosol. This is carried into the plasma by an ai on flow after passing through a... 

Detection limits in ICPMS depend on several factors. Dilution of the sample has a lai e effect. The amount of sample that may be in solution is governed by suppression effects and tolerable levels of dissolved solids. The response curve of the mass spectrometer has a large effect. A typical response curve for an ICPMS instrument shows much greater sensitivity for elements in the middle of the mass range (around 120 amu). Isotopic distribution is an important factor. Elements with more abundant isotopes at useful masses for analysis show lower detection limits. Other factors that affect detection limits include interference (i.e., ambiguity in identification that arises because an elemental isotope has the same mass as a compound molecules that may be present in the system) and ionization potentials. Elements that are not efficiently ionized, such as arsenic, suffer from poorer detection limits. 

Another type of interference in ICPMS is suppression of the formation of ions from trace constituents when a large amount of analyte is present. This effect depends on the mass of the analyte The heavier the mass the worse the suppression. This, in addition to orifice blockage from excessive dissolved solids, is usually the limiting factor in the analysis of dissolved materials. 

Direct sampling of solids may be carried out using laser ablation. In this technique a high-power laser, usually a pulsed Nd-YAG laser, is used to vaporize the solid, which is then swept into the plasma for ionization. Besides not requiring dissolution or other chemistry to be performed on the sample, laser ablation ICPMS (LA-ICPMS) allows spatial resolution of 20-50 pm. Depth resolution is 1-10 pm per pulse. This aspect gives LA-ICPMS unique dit nostic capabilities for geologic samples, surface features, and other inhomogeneous samples. In addition minimal, or no, sample preparation is required. 

One of the important advantages of ICPMS in problem solving is the ability to obtain a semiquantitative analysis of most elements in the periodic table in a few minutes. In addition, sub-ppb detection limits may be achieved using only a small amount of sample. This is possible because the response curve of the mass spectrometer over the relatively small mass range required for elemental analysis may be determined easily under a given set of matrix and instrument conditions. This curve can be used in conjunction with an internal or external standard to quantily within the sample. A recent study has found accuracies of 5—20% for this type of analysis. The shape of the response curve is affected by several factors. These include matrix (particularly organic components), voltages within the ion optics, and the temperature of the interffice. 

Full quantitation is accomplished in the same manner as for most analytical instrumentation. This involves the preparation of standard solutions and matching of the matrix as much as possible. Since matrix interferences are usually minimized in ICPMS (relative to other techniques), the process is usually easier. 

ICPMS is uniquely able to borrow a quantitation technique from molecular mass spectrometry. Use of the isotope dilution technique involves the addition of a spike having a different isotope ratio to the sample, which has a known isotope ratio. This is usefiil for determining the concentration of an element in a sample that must undergo some preparation before analysis, or for measuring an element with high precision and accuracy. ... 

ICPMS is a relatively new technique that became usefiil and commercially available early in its development. As a result, the field is continually changing and grotving. The following is a summary of the directions of ICPMS instrumentation as described by three commercial instrument representatives. ... 

ICPMS, although a young technique, has become a powerful tool for the analysis of a variety of materials. New applications are continually being developed. Advantages include the ability to test for almost all elements in a very short time and the high sensitivity of the technique. 

ICP-OES is a destructive technique that provides only elemental composition. However, ICP-OES is relatively insensitive to sample matrix interference effects. Interference effects in ICP-OES are generally less severe than in GFAA, FAA, or ICPMS. Matrix effects are less severe when using the combination of laser ablation and ICP-OES than when a laser microprobe is used for both ablation and excitation. 

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