MS detection techniques

Analytical methods for quantifying americium in environmental samples are summarized in Table 7-2. The methods that are commonly used in the analysis of americium based on activity are gross a analysis, a-spectrometry and gamma-ray spectrometry. MS detection techniques are used to measure the mass of americium in environmental samples. (The mass-activity conversion factor for 241Am is 0.29 (lCi/ lg or 3.43 ig/ p,Ci [Harvey etal. 1993]). 

Application of LC-MS/MS techniques to the analysis of phthalate ester metabolites in urine have also been developed. For example, Blount et al. (2000b) have developed an assay to quantify the monoester metabolites (including MEHP) of eight phthalate diesters in urine, utilizing HPLC coupled with atmospheric pressure chemical ionization and tandem mass spectrometric (APCI-MS/MS) detection techniques. Urine samples were treated with -glucuronidase to release the free phthalate monoesters followed by a two-step solid phase extraction procedure. After evaporative concentration of the eluant, the analytes in the purified samples are further separated on a phenyl reverse phase HPLC column and quantified by APCI-MS/MS, following careful optizimation of the APCI-MS/MS instrument. The limits of detection for MEHP were determined to be 1.2 ng/ml urine with recovery efficiencies of between 78 and 91%. 

The MS detection technique is based on the ionization and fragmentation of an analyte. The mass analyzer separates the molecular ion and fragments according to their mass-to-charge ratios. Usually the detector output represents the total ion current produced by all fragments and molecular ions. Of course, this technique can be considered universal because all molecules can be sensed. However, if a particular ion that epitomizes a certain analyte (or class of analytes) is specifically sensed (via selected ion monitoring operation) while all other ions are disregarded, the technique becomes very specific. 

Analysis times can be almost an hour per injection by capillary GC. Fast-GC methods for the analysis of PAHs include the use of more selective stationary phases, two-dimensional GC (GC X GC), short narrow-bore capillary columns, selective detection, advanced MS detection techniques, and faster temperature programming. Faster column heating at 100°C min from 50 to 320°C has been achieved with resistive heating of a 5 m X 0.25 mm i.d. 5% phenyl methylpolysiloxane capillary column inside a metal tube. ° This apparatus was used to separate a mixture of the EPAis in under 4 min. Although geometric isomers were not resolved, the method could be an effective screening tool. With FID detection, LODs of 5 pg /rl were demonstrated for PAHs. 

AEOs spiked into raw wastewaters were applied to elaborate an APCI or ESI-LC-MS method to determine non-ionic surfactants after SPE. Ionisation efficiencies of both interface types were compared and the more effective APCI technique then was applied for quantification [334]. Recoveries observed with standard determination methods for surfactants and MS detection techniques for different types of surfactants (e.g. alkylether carboxylates, sulfosuccinates, fatty acid polyglycol amines, quaternary carboxoalkyl ammonium compounds, modified AEOs, EO/ PO compounds, APGs, alkyl polyglucamides, betaine and sulfobetaine) in spiked wastewater samples were compared by applying APCI and/or ESI(-i-/-).Poor recoveries were obtained by standard methods but good results by MS [335]. APCI and... 

When these high-sensitivity MS detection techniques are coupled to HPLC-FAB-MS, exciting prospects will be opened up for picomole mass spectrometric studies on neuropeptides. 

The majority of MS detection techniques for biological toxins involve collecting water samples for LC-MS and LC-MS/MS methods. Of these techniques, many have been developed with a focus on detecting biological toxins in environmental samples (e.g., natural waters), but these methods can be applied to drinking waters and any body of water that needs to be monitored and secured from these threats. In particular, sample preparation may need to be tailored to the sample matrix of interest, be it natural or treated water. 

Samples made from model formula 1 were determined to be non-FDA compliant with both GC-MS and LC-MS methods in both direct and indirect extraction tests. For samples made from formula 2, the results are quite different with the different methods. With results from the GC-MS method, the sample made from formula 2 could easily be determined as FDA compliant (through the no migration exemption) for both direct and indirect applications, while results from the LC-MS method only allows its use for indirect food packaging applications under the Functional Barrier Doctrine exemption. Samples made from Formula 3, on the other hand, are determined to be FDA compliant (through the no migration statutory exemption) even with the more stringent LC-MS method. It can be seen that only with the LC-MS detection technique can one clearly determine the actual level of migration especially when there are non-volatile species involved. 

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. 

Two detection techniques were tested, LIBS for the Cu-Ag-Si samples and LA-TOF-MS for the TiN-TiAlN samples. 

Multidimensional gas chromatography has also been used in the qualitative analysis of contaminated environmental extracts by using spectral detection techniques Such as infrared (IR) spectroscopy and mass spectrometry (MS) (20). These techniques produce the most reliable identification only when they are dealing with pure substances this means that the chromatographic process should avoid overlapping of the peaks. 

Once the analyte has been separated from the matrix in LC, the best approach to the detection of the molecule must be determined. This section will discuss the detection techniques of ultraviolet/visible (UVA IS), fluorescence (FL), and electrochemical (EC) detection, with MS being addressed separately in Section 4.2. When deciding on the most appropriate detector for an LC separation, the appropriate chemical data on the analyte should be collected by using a spectrophotometer, fluorimeter, and potentiometer. 

Analytical methods for parent chloroacetanilide herbicides in soil typically involve extraction of the soil with solvent, followed by solid-phase extraction (SPE), and analysis by gas chromatography/electron capture detection (GC/ECD) or gas chromatog-raphy/mass spectrometry (GC/MS). Analytical methods for parent chloroacetanilides in water are similarly based on extraction followed by GC with various detection techniques. Many of the water methods, such as the Environmental Protection Agency (EPA) official methods, are multi-residue methods that include other compound classes in addition to chloroacetanilides. While liquid-liquid partitioning was used initially to extract acetanilides from water samples, SPE using... 

All previous discussion has focused on sample preparation, i.e., removal of the targeted analyte(s) from the sample matrix, isolation of the analyte(s) from other co-extracted, undesirable sample components, and transfer of the analytes into a solvent suitable for final analysis. Over the years, numerous types of analytical instruments have been employed for this final analysis step as noted in the preceding text and Tables 3 and 4. Overall, GC and LC are the most often used analytical techniques, and modern GC and LC instrumentation coupled with mass spectrometry (MS) and tandem mass spectrometry (MS/MS) detection systems are currently the analytical techniques of choice. Methods relying on spectrophotometric detection and thin-layer chromatography (TLC) are now rarely employed, except perhaps for qualitative purposes. 

The principal limitation in the use of electrophoretic techniques is the lack of availability of suitable detection systems for quantitative analysis and unequivocal identification of pesticide analytes. Traditionally, either ultraviolet/visible (UVA IS) or fluorescence detection techniques have been used. However, as with chromatographic techniques, MS should be the detection system of choice. A brief comparison of the numbers of recent papers on the application of GC/MS and LC/MS with capillary elec-trophoresis/mass spectrometery (CE/MS) demonstrates that interfaces between CE... 

Balogh, M.P and Li, J.B., HPLC Analysis of hypericin with photodiode-array and MS detection the advantages of multispectral techniques, LC-GC, 17(6), 558, 1999. 

Note that the interfacing of LC techniques with MS puts significant constraints on the solvents that can be used i.e., they must be volatile, with a low salt concentration, for MS compatibility. Narrow-bore columns, which use much smaller amounts of salt and organic modifier, appear to have potential for facilitating IEC-MS applications.40 Despite the excellent sensitivity of MS detection for most elements, however, there are cases where matrix effects can interfere. In this situation, combination of IEC with atomic emission spectrometry (AES) or atomic absorption spectrometry (AAS) may be preferable, and can also provide better precision.21 32 4142 Other types of... 

Current trends in GC relate to miniaturisation, fast-GC, improved selectivity (mainly for short columns), stability of column stationary phases (reduction of bleeding) and increasing use of MS detection [117]. Finally, GC can be readily hyphenated with spectroscopic techniques without using involved interfaces and thus can easily provide unambiguous solute identification. 

HPLC (in both NP and RP modes) is quite suitable for speciation by coupling to FAAS, ETAAS, ICP-MS and MIP-MS [571,572]. Coupling of plasma source mass spectrometry with chromatographic techniques offers selective detection with excellent sensitivity. For HPLC-ICP-MS detection limits are in the sub-ng to pg range [36]. Metal ion determination and speciation by LC have been reviewed [573,574] with particular regard to ion chromatography [575]. 

---