Mass spectrometry limitations

Lindane Application of gas chromatography-mass spectrometry. Limit of detection 0.1 xg/kg [170]... 

High-resolution gas chromatography-mass spectrometry, limit of detection low ppb High-performance liquid chromatography [457]... 

Bandy, Tucher, and Moroulis" used Carbosive B. In combination with mass spectrometry, limits of detection at the ppt level were achieved. 

Following the movement of airborne pollutants requires a natural or artificial tracer (a species specific to the source of the airborne pollutants) that can be experimentally measured at sites distant from the source. Limitations placed on the tracer, therefore, governed the design of the experimental procedure. These limitations included cost, the need to detect small quantities of the tracer, and the absence of the tracer from other natural sources. In addition, aerosols are emitted from high-temperature combustion sources that produce an abundance of very reactive species. The tracer, therefore, had to be both thermally and chemically stable. On the basis of these criteria, rare earth isotopes, such as those of Nd, were selected as tracers. The choice of tracer, in turn, dictated the analytical method (thermal ionization mass spectrometry, or TIMS) for measuring the isotopic abundances of... 

For a limited range of substances, negative radical anions (M ) can be formed rather than positive ions (Equation 3.3). Negative radical anions can be produced in abundance by methods other than electron ionization. However, since most El mass spectrometry is concerned with positive ions, only they are discussed here. 

Although there has been some controversy concerning the processes involved in field ionization mass spectrometry, the general principles appear to be understood. Firstly, the ionization process itself produces little excess of vibrational and rotational energy in the ions, and, consequently, fragmentation is limited or nonexistent. This ionization process is one of the mild or soft methods available for producing excellent molecular mass information. The initially formed ions are either simple radical cations or radical anions (M ). 

Samples to be examined by inductively coupled plasma and mass spectrometry (ICP/MS) are commonly in the form of a solution that is transported into the plasma flame. The thermal mass of the flame is small, and ingress of excessive quantities of extraneous matter, such as solvent, would cool the flame and might even extinguish it. Even cooling the flame reduces its ionization efficiency, with concomitant effects on the accuracy and detection limits of the ICP/MS method. Consequently, it is necessary to remove as much solvent as possible which can be done by evaporation off-line or done on-line by spraying the solution as an aerosol into the plasma flame. 

When mass spectrometry was first used as a routine analytical tool, El was the only commercial ion source. As needs have increased, more ionization methods have appeared. Many different types of ionization source have been described, and several of these have been produced commercially. The present situation is such that there is now only a limited range of ion sources. For vacuum ion sources, El is still widely used, frequently in conjunction with Cl. For atmospheric pressure ion sources, the most frequently used are ES, APCI, MALDI (lasers), and plasma torches. 

Until 1981, mass spectrometry was limited, generally, to the analysis of volatile, relatively low-molecular-mass samples and was difficult to apply to nonvolatile peptides and proteins without first cutting them chemically into smaller volatile segments. During the past decade, the situation has changed radically with the advent of new ionization techniques and the development of tandem mass spectrometry. Now, the mass spectrometer has a well-deserved place in any laboratory interested in the analysis of peptides and proteins. 

There is no theoretical upper limit on m/z that can be examined, and TOF mass spectrometry is useful for substances having very high molecular mass. In practice, the current upper limit is about 350,000. Unfortunately, ions even of the same m/z value do have a spread of velocities after acceleration, so the resolution achievable with TOF is not very high because bunches of ions of one m/z value overlap those at the next m/z value. 

Environment. Detection of environmental degradation products of nerve agents directly from the surface of plant leaves using static secondary ion mass spectrometry (sims) has been demonstrated (97). Pinacolylmethylphosphonic acid (PMPA), isopropylmethylphosphonic acid (IMPA), and ethylmethylphosphonic acid (EMPA) were spiked from aqueous samples onto philodendron leaves prior to analysis by static sims. The minimum detection limits on philodendron leaves were estimated to be between 40 and 0.4 ng/mm for PMPA and IMPA and between 40 and 4 ng/mm for EMPA. Sims analyses of IMPA adsorbed on 10 different crop leaves were also performed in order to investigate general apphcabiflty of static sims for... 

The complex of the following destmctive and nondestmctive analytical methods was used for studying the composition of sponges inductively coupled plasma mass-spectrometry (ICP-MS), X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and atomic absorption spectrometry (AAS). Techniques of sample preparation were developed for each method and their metrological characteristics were defined. Relative standard deviations for all the elements did not exceed 0.25 within detection limit. The accuracy of techniques elaborated was checked with the method of additions and control methods of analysis. 

The liquid chromatography - tandem mass spectrometry (LC/MS/MS) technique was proposed for the determination of corticosteroids in plasma and cerebrospinal fluid (CSF, liquor) of children with leucosis. Preliminai y sample prepai ation included the sedimentation of proteins, spinning and solid-phase extraction. MS detection was performed by scanning selected ions, with three chai acteristic ions for every corticosteroids. The limit of detection was found 80 pg/ml of plasma. 

Inductively coupled plasma-mass spectrometry (ICP-MS) is a multielement analytical method with detection limits which are, for many trace elements, including the rare earth elements, better than those of most conventional techniques. With increasing availability of ICP-MS instalments in geological laboratories this method has been established as the most prominent technique for the determination of a large number of minor and trace elements in geological samples. 

Laser ionization mass spectrometry or laser microprobing (LIMS) is a microanalyt-ical technique used to rapidly characterize the elemental and, sometimes, molecular composition of materials. It is based on the ability of short high-power laser pulses (-10 ns) to produce ions from solids. The ions formed in these brief pulses are analyzed using a time-of-flight mass spectrometer. The quasi-simultaneous collection of all ion masses allows the survey analysis of unknown materials. The main applications of LIMS are in failure analysis, where chemical differences between a contaminated sample and a control need to be rapidly assessed. The ability to focus the laser beam to a diameter of approximately 1 mm permits the application of this technique to the characterization of small features, for example, in integrated circuits. The LIMS detection limits for many elements are close to 10 at/cm, which makes this technique considerably more sensitive than other survey microan-alytical techniques, such as Auger Electron Spectroscopy (AES) or Electron Probe Microanalysis (EPMA). Additionally, LIMS can be used to analyze insulating sam-... 

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