IPC-MS

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. 

1 ml/min eluent flow = 500ml/min of gas at flow STP Inorganic buffers and IPRs 25 to 50°C All analytes 

Accepts only 10 ml/min gas flow Volatile mobile phase components 200to350°C Volatile analytes 

From the analysis of the specifications in Table 12.2, IPC - MS hyphenation requires (1) specific optimization of mobile phase composition, selecting only volatile components, (2) devising strategies to minimize eluent fiow, and (3) an interface to make IPC effluent amenable to MS detection. The goals of the interface are (1) separation of the analyte from the bulk eluent, (2) ion evaporation for ionic species or ionization of non-ionic solutes, and (3) fragmentation and quantitative transfer of analyte fragments to the mass analyzer. 

An ideal interface should not cause extra-column peak broadening. Historical interfaces include the moving belt and the thermospray. Common interfaces are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCl). Several special interfaces include the particle beam—a pioneering technique that is still used because it is the only one that can provide electron ionization mass spectra. Others are continuous fiow fast atom bombardment (CF-FAB), atmospheric pressure photon ionization (APPI), and matrix-assisted laser desorption ionization (M ALDl). The two most common interfaces, ESI and APCI, were discovered in the late 1980s and involve an atmospheric pressure ionization (API) step. Both are soft ionization techniques that cause little or no fragmentation hence a fingerprint for qualitative identification is usually not apparent. 

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Venth K, Danzer K, Kudermann G, Blaufufi K-H (1996) Multisignal evaluation in IPC-MS. Determination of trace elements in Mo-Zr-alloys. Fresenius J Anal Chem 354 811... 

Liquid chromatography mass spectrometry (LC-MS) is now routinely used in analytical laboratories. Traditional IPRs are non-volatile salts that are not compatible with MS techniques because they play a major role in source pollution that is responsible for reduced signals. Moreover the final number of charged ions that reach the detector is impaired by ion-pair formation actually IPRs added to the mobile phase to improve analytes retention exert a profound effect on analyte ionization. Chromatographers who perform IPC-MS must optimize the eluent composition based on both chromatographic separation and compatibility with online detection requirements. 

Different strategies devised for effective IPC-MS methods are discussed in greater detail in Chapter 14. This chapter examines the advantages of using volatile... 

Linally, we must emphasize that ILs are certainly not the additives of choice for IPC-MS applications because their non-volatility will create condensation and pollution in the ionization sources. Moreover, slight UV absorbance may limit the use of UV detectors. 

The addition of many classes of IPRs leads to a modification of the eluent pH. Volatile amines, greatly appreciated for their volatility in IPC-MS use, increase the eluent pH. Conversely, using perfluorinated acids of different chain length as IPRs for basic analytes involves a concomitant lowering of the eluent pH that in turn provides the protonation the basic analytes need under IPC conditions. The IPR counter ion is also important when dealing with eluent pH for example, the behavior of tetrabutylam-monium hydroxide would be very different from that of the corresponding chloride. 

Positive (-I-) and Negative (-) Features of Most Common Interfaces Used for IPC-MS Combination... 

ESI is the most common interface since IPC and MS were coupled initially. By 2008, most applications IPC-MS used the ESI interface [58,68-82] because analytes amenable to IPC are usually already ionic in the column effluent that enters the interface. Examples of APCI-MS applications [83,84] include two-fold use of both interfaces [85] they gave similar results in the determination of polyunsatured fatty acid monoepoxides [86]. For determining mono- and di-sulfonated azo dyes, ESI proved to give the best performance in terms of sensitivity and reproducibility [83]. Joining negative APCI-MS and ESI-MS unambiguously identified several acidic oxidation products of 2,4,6-trinitrotoluene in ammunition, wastewater, and soil extracts [61]. 

IPC-MS combined methods must be optimized with respect to separation and compatibility with online detection involving the constraints detailed in Table 12.2 regarding the composition and volatility of the mobile phase. The major concern of chromatographers who deal with this combined technique is the reduced signal caused by source pollution of non-volatile IPRs. Moreover, the efficiency of droplet development, which in turn affects the number of charged ions that ultimately reach... 

Chapter 11, is valuable because it dramatically reduces operation costs because no IPR is needed in the eluent and IPC-MS is straightforward. The absence of IPR in the eluent minimizes ionization suppression in the MS source, thus increasing the sensitivity of the method [60,105-107]. 

IPC-MS/MS was used to quantify heterocyclic aromatic amines in meat-based infant foods [30], The separation of biogenic amines was chemometrically optimized when they were determined in wines [31] a sensitive and selective method to determine 12 biogenic amines regardless of the characteristics of the vegetal food matrix was successfully validated [32], Determination of soybean proteins in commercial products was performed by fast IPC using an elution gradient and acetic acid as the IPR [33],... 

Glycopeptides from a peptide mixture were analyzed via normal phase IPC, using inorganic monovalent ions as IPRs (added only to the sample and not to the mobile phase) to increase the hydrophobicity differences among peptides and glycopeptides [63]. IPC separation of peptides usually relies on the use of perlluorinated carboxylic acids [64] and small chaotropes [65,66], It can be performed also on a preparative scale for the purification of peptides from natural sources [67], Amino acids and related compounds [68-72] were similarly analyzed via IPC-MS. 

An IPC-MS/MS spectrometric method to determine ethephon residues in vegetables included an IPR-free mobile phase the IPR was added directly to the sample solution to minimize ionization suppression in the MS source and increase the sensitivity of the method [106],... 

A cross-validation study showed comparable levels of adefovir and its metabolites determined by IPC-MS/MS or radioactivity detection. The optimized IPC strategy was sufficiently sensitive, accurate, and precise to serve as a useful tool for studying the intracellular pharmacology of adefovir [14]. 

For the bulk analysis of metallic elements in atmospheric particles, spectroscopic methods (e.g., AAS, ICP-OES, IPC-MS, XRF, PIXE, SSMS) are widely used (Part V, Chapter 2). Here, sample preparation is a crucial... 

Edmonds, J.S., Shibata, Y., Francesconi, K.A., Yoshinaga, J. and Morita, M. (1992). Arsenic lipids in the digestive gland of the western rock lobster Panullrus cygnus an investigation by HPLC IPC-MS, Sci. Total Environ. 122, 321-335. 

The method of choice for the determination of most vitamins is HPLC due to its high separation capability, its mild analytical conditions, and the possibility to use various specifically adapted detection methods, e.g., LTV, fluorescence, or MS detection. All fat-soluble vitamins and most water-soluble vitamins have chromophores suitable for UV detection. Separation of vitamers and stereoisomers can be achieved. If a higher sensitivity is required HPLC with fluorescence detection can be used, either directly (e.g., vitamins A and E) or after derivatization (e.g., thiamine). A further improvement in sensitivity and specificity has been achieved by introducing HPLC with mass spectrometric detection in vitamin analysis. Due to the structural information retrievable, e.g., molecular mass, fragmentation pattern, this is the method of choice for analysis of samples with complex mixtures or low vitamin concentrations. Examples for the use of HPLC-MS in vitamin analysis include the determination of 25-hydroxy-D3 and pantothenic acid. However, one drawback of mass spectrometry is the need for an isotopically labeled reference compound for reliable quantification. Due to the structural complexity of many vitamins, these reference compounds are often expensive and difficult to synthesize. An interesting unique application is the determination of vitamin B12 by HPLC-IPC-MS, which is possible due to its cobalt content. 

A novel technique of atomisation, known as vapour generation via generation of the metal hydride, has been evolved, which has increased the sensitivity and specificity enormously for these elements [5-7]. In these methods the hydride generator is linked to an AAS (flame graphite furnace) or inductively coupled plasma-optical emission spectrometer (ICP-OES) or an inductively coupled plasma mass spectrometer (IPC-MS). Typical detection limits achievable by these techniques range from 3 pg/1 (arsenic) to 0.09 pg/1 (selenium). 

Heavy metals are most commonly determined by IGP-AES, IPC-MS, atomic absorption (AA), and X-ray fluorescence techniques. 

Zheng J, lij ima A, Furuta N (2001) Complexation effect of antimony compounds with citric acid and its application to the speciation of antimony(III) and antimony(V) using HPLC-IPC-MS. J Anal At Spectrom 16 812-818... 

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