Surface-Activated Chemical Ionization

In an investigation of the effect of several instrumental parameters on the efficiency of SACI, most attention was paid to the evaluation of vaporization parameters to test the hypothesis that ion evaporation can play an important role in the SACI mechanism. The data so obtained partially supported this hypothesis by increasing the flow rates of 

After that investigation, a series of questions naturally arose that led to the need to understand the real role of the surface. Is it an active region for sample ionization, or does it simply behave as an electrostatic mirror leading to better focusing into the entrance capillary orifice of ions previously produced If the latter hypothesis is true, how are the ions generated  

The kinetic energies of the vaporized species were evaluated by simple calculations, performed on the basis of the experimental setup They are in the 1-10-meV range, at least three order of magnitude less than those necessary to promote effective gas-phase collision-induced ionization and decomposition processes and, consequently, collisional phenomena cannot be held responsible for ion production. 

another aspect was considered, moving from the physical to a chemical phenomenon. At 20 °C, the dissociation constant for water (pKw) is 14.1669, while it is 13.0171 at 60°C and 12.4318 at 90°C. Considering that 

To investigate these ideas, a simple experiment based on the deposition on the metallic surface of a thin layer of deuterated glycerol was performed. Under this condition, when the analysis of the PHGGGWGQPHGGGWGQ peptide was performed by SACI, the signal of the [M + D+] ion at m/z 1573 was observed to dominate (Fig. 1.19). This evidence is good for the participation of the chemicals present on the surface in the ionization phenomena occurring in SACI. 

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Cristoni S, Bernardi LR, Gerthoux P, Gonella E, MocareUi P. 2004. Surface-activated chemical ionization ion trap mass spectrometry in the analysis of amphetamines in diluted urine samples. Rapid Commun Mass Spectrom 18 1847. 

Recently, a LC/MS method to determine OTA in wine and grape extracts by using Surface-Activated-Chemical-Ionization and multistage fragmentation mass spectrometry (LC/SACI-MS3), was proposed (Flamini et al., 2007). SACI is an ionization source developed to analyze medium-high polar compounds in a wide range of m/z ratios (100-4000 Da). This device, used in determination of compounds such as... 

Flamini, R., Dalla Vedova, A., De Rosso, M. and Panighel, A. (2007) A New Sensitive and Selective Method for Analysis of Ochratoxin A in Grape and Wine by direct liquid chromatography/surface activated chemical ionization-tandem mass spectrometry, Rapid Commun. Mass Spectrom. 21(22), 3737-3742. 

Cristoni, S., Rossi Bernardi, L., Guidugli, F., Tubaro, M., and Traldi, P. (2005). The role of different phenomena in surface-activate chemical ionization (SACI) performance, J. Mass Spectrom., 40,1550-1557. 

Figure 8.3. The SACI/MS2 and MS3 fragmentation patterns of OTA and ZAN [M+H]+ ions. (Reprinted from Rapid Communications in Mass Spectrometry 21, Flamini et al., A new sensitive and selective method for analysis of och-ratoxin A in grape and wine by direct liquid chromatography/surface activated chemical ionization-tandem mass spectrometry, p. 3738, Copyright 2007, with permission from John Wiley Sons, Ltd.)...

Several formal and informal intercomparisons of nitric acid measurement techniques have been carried out (43-46) these intercomparisons involve a multitude of techniques. The in situ measurement of this species has proven difficult because it very rapidly absorbs on any inlet surfaces and because it is involved in reversible solid-vapor equilibria with aerosol nitrate species. These equilibria can be disturbed by the sampling process these disturbances lead to negative or positive errors in the determination of the ambient vapor-phase concentration. The intercomparisons found differences of the order of a factor of 2 generally, and up to at least a factor of 5 at levels below 0.2 ppbv. These studies clearly indicate that the intercompared techniques do not allow the unequivocal determination of nitric acid in the atmosphere. A laser-photolysis, fragment-fluorescence method (47) and an active chemical ionization, mass spectrometric technique (48) were recently reported for this species. These approaches may provide more definite specificity for HN03. Challenges clearly remain in the measurement of this species. 

Polyhydroxy acids are another group of biopolymers. Since polylactic acids, polyglycolic acid, and poly(citric acid) are classified as thermoplastic polyesters (saturated), they lack reactive functional groups for surface reactions. Moreover, any chemical manipulation to create activation sites results in hydrolysis of the ester bonds. The only reported successful methods for functionalization of polyhydroxy acids are blending them with ECPs, or using a plasma polymerization process [29]. Prior to the plasma polymerization process, surface activation or ionization of these biopolymers must be carried out, which is acquired by means of vapor phase deposition, laser deposition, microwave or synchrotron radiation [30], pulsed arc, pulsed combustion, spark, or friction induction [30], electron beams, plasma induction, corona, photons, ion beams, and X-rays [25]. 

Perfluorinated carboxylic acids are corrosive liquids or solids. The acids are completely ionized in water. The acids are of commercial significance because of their unusual acid strength, chemical stabiUty, high surface activity, and salt solubiUty characteristics. The perfluoroaLkyl acids with six carbons or less are hquids the higher analogues are soHds (Table 1). 

The possible mechanism of ionization, fragmentation of studied compound as well as their desoi ption by laser radiation is discussed. It is shown that the formation of analyte ions is a result of a multi stage complex process included surface activation by laser irradiation, the adsoi ption of neutral analyte and proton donor molecules, the chemical reaction on the surface with proton or electron transfer, production of charged complexes bonded with the surface and finally laser desoi ption of such preformed molecules. 

A9.5.2.4.1 For organic substances experimentally derived high-quality Kow values, or values which are evaluated in reviews and assigned as the recommended values , are preferred over other determinations of Kow. When no experimental data of high quality are available, validated Quantitative Structure Activity Relationships (QSARs) for log Kow may be used in the classification process. Such validated QSARs may be used without modification to the agreed criteria if they are restricted to chemicals for which their applicability is well characterized. For substances like strong acids and bases, substances which react with the eluent, or surface-active substances, a QSAR estimated value of Kow or an estimate based on individual -octanol and water solubilities should be provided instead of an analytical determination of Kow (EEC A.8., 1992 OECD 117, 1989). Measurements should be taken on ionizable substances in their non-ionized form (free acid or free base) only by using an appropriate buffer with pH below pK for free acid or above the pK for free base. 

Cristoni, S., Bernardi, L.R., Biunno, I., Tubaro, M. and Guidugli, F. (2003) Surface-activated no-discharge atmospheric pressure chemical ionization, Rapid Commun. Mass Spectrom. 17(17), 1973-1981. 

In the recent past, receptors and drug-reeeptor interaetions theories have highlighted the importance of physical and chemical characteristics with regard to drug action. Such salient features may include partition coefficients, solubility, degree of ionization, isosterism and bio-isosterism, surface activity, thermodynamic activity, intramolecular and intermolecular forces, redox potentials, stereochemisty and interatomic distances between various funetional groups. 

Several methods have been developed specifically for naphthenic acids, a class which includes the surface active carboxylate surfactants. Naphthenic acids are present as a complex mixture of a number of homologues with only a small range in molar mass (166-450 mol/g), little change in solubility character, and have been difficult to assay using conventional analytical methods. Methods such as negative ion-mode mass spectrometry using fast atom bombardment (FABMS), have been successfully applied to the analysis of naphthenic acid mixtures [93, 94], Other promising techniques include fluoride ion chemical ionization mass spectrometry (FI-MS) [95], and electrospray ionization mass spectrometry (ESIMS), which may allow for the quantification of the various naphthenic acid fractions [96]. 

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