Adduct ion

Typical Cl processes in which neutral sample molecules (M) react with NH to give either (a) a protonated ion [M + HJ or (b) an adduct ion [M + NHJ+ the quasi-molecular ions are respectively 1 and 18 mass units greater than the true mass (M). In process (c), reagent ions (CjHf) abstract hydrogen, giving a quasi-molecular ion that is 1 mass unit less than M. 

Adduct ion. An ion formed by interaction of two species, usually an ion and a molecule, and often within the ion source, to form an ion containing all the constituent atoms of one species as well as an additional atom or atoms. 

If the molecular species were at m/z 195 (case (b) above) the ion of m/z 163 is generated by a loss of 32 Da. A similar loss from the adduct ion would not be unusual, in this case an ion at m/z (217 — 32), i.e. m/z 185 would be expected. No significant ion of this m/z value is observed and while this is not conclusive it would suggest that this is not the explanation. 

Adduct ion An ion arising from the combination of two species, e.g. the molecular species observed in a positive-ion APCI spectrum is usually an adduct of the analyte molecule with a species such as H+, Na+ or NH4+. 

Ion-molecule reaction The reaction between an ion and a neutral molecule which leads to the production of an adduct ion. 

The bleaching of carotenoids was simultaneous with the formation of near-infrared absorbing intermediates in the microsecond timescale. The formation of an adduct ion-pair is instantaneous during the laser pulse (<10ns) with maximum absorption in the region 830-950 nm, depending on... 

Analytical methods for the detection of residues of semicarbazide use derivatisation with 2-nitrobenzaldehyde and LC-MS detection. Figure 18 shows the positive ESI response for a 1 ppm solution of semicarbazide after derivatisation and concentration. The main peak 2 at 16 min shows the expected 209 (M+H)+ ion of the 2-nitrobenzaldehyde derivative of semicarbazide together with its sodium adduct ion at m/z 231 (Figure 19). 

Owing to soft conditions, the mass spectra obtained by this kind of ionization techniques are also characterized by the presence of adduct ions, i.e. ionic species formed by weak interactions between the ions and other chemical species (see below). 

If during the ionization the amount of energy deposited on the molecule is low, as occurs in soft techniques, i.e. Cl, ESI, DESI and MALDI, the mass spectrum is very simple. It is characterized by protonated/deprotonated molecules, and eventually few adduct ions but very few or no fragment ions. This implies that it is easy to obtain the molecular weight of the analyte under investigation, but structural information is missing. As an example, the ESI mass spectrum of a small molecule is reported in Figure 2.20. There are two main ions one at m/z 556 and another at m/z 578. As the mass spectrum has been obtained in positive... 

Adduct ions are quite frequent in the mass spectra. In positive ion mode, sodium or potassium cluster ions are commonly found. Mineral compounds often lead to multiple cluster ions. For example, spectra of FeCl3 in negative ion mode lead to several peaks from m/z 35 (Cl ) to m/z 487 ([(FeCl3)2FeCl3] ) [Van Ham et al. 2004],... 

Figure 1. The electrospray positive ion spectrum of 5, 10, 15, 20 tetraphenyl-21//,23//-porphine lead (II) showing the Na+ and K+ adducts. The expanded portion shows the resolution of the Na+ adduct ion isotope pattern.

Dehydrogenation of substituted benzene molecules has also been observed, thus Sc+ and Ti+ react with toluene (129) to form adduct ions involving loss of a hydrogen molecule, [MC7H6]+. Simple addition occurs in the reaction of V+ with toluene, [VC7H ]+, similar to the reaction of V+ with benzene. The reactions of many of the lanthanide ions, Sc+ and Y+, with 1,3,5-tri-terf-butylbenzene produce ions showing that dehydrogenation has occurred (130). 

Substitution of S for O in the [MoXJ+ (x = 1-3) ions reduces the reactivity of the ions (184). The major ions produced when [MoS]+ and [MoS2]+ were reacted with benzene were the adduct ions [MoSxC6I I6 + [MoS3]+ was unreactive in contrast to [Mo03]+. 

TSI. The liquid is converted into a vapour jet and small droplets are generated with the help of a heated vapouriser tube. A buffer dissolved in the eluent assists the ionisation process through the formation of adduct ions, which are produced via statistical charging of individual droplets. Due to the softness of the procedure, no structurally characteristic fragments, which could aid identification of unknown compounds, are formed. 

One of the most serious drawbacks that has been observed in the ionisation processes with soft ionisation techniques is the very soft generation of ions. This process, which predominately leads to molecular ions or adduct ions but no fragments for identification, however, was also used to improve and speed-up MS analysis. 

Equidistant or clustered signals, characteristic of some anionic, nonionic or cationic surfactants (cf. Fig. 2.5.1(a) and (b). So the presence of non-ionic surfactants of alkylpolyglycolether (alcohol ethoxylate) type (AE) (structural formula C H2 i i-0-(CH2-CH2-0)x-H) could be confirmed in the formulation (Fig. 2.5.1(a)) applying APCI-FIA-MS in positive mode. AE compounds with high probability could also be assumed in the heavily loaded environmental sample because of the patterns of A m/z 44 equally spaced ammonium adduct ions ([M + NH4]+) shown in its FIA-MS spectrum in Fig. 2.5.1(b). 

CnH2n+i-0-(CH2-CH2-0)x-S03 now could be observed as [M + NH4]+ ions at a RTof 3.8-5.0 min. Signal intensity was quite low but a wide range of alkyl ethoxylated sulfate compounds, starting at m/z 372 and ending at 680 and AES ammonium adduct ions with 3-10 EO units were recorded. With an elevated intensity as observed under APCI(+) ionisation, the [M + NH4]+ions of the non-ionics AEhomologue mixture were observed in Fig. 2.5.11(b) at a RT of 7-10 min. 

NPEOs and OPEOs (rcEo = 3-10) as industrial blends or standard compound (Triton X-100), respectively, were separated together with linear alkylbenzene sulfonates (LASs) on a Ci-RP column [10]. The intensive ions that could be observed in the spectra were mono-, di- and tri-sodium adduct ions [M + Na]+ (m/z 581), [M + 2Na]+ (m/z 604) and [M + 3Na]+ (m/z 626) of the EO7 homologue. The intensity of the molecular [M + H]+-ion, however, was small compared with the sodium adduct ions. The compounds had been concentrated prior to separation on Cis and SAX SPE cartridges. Samples from river water were handled in the same way. 

Ion masses (m/z) of different molecular and adduct ions of alkyl mono- and diglucosides (as assigned in Figs. 2.7.2 and 2.7.5) (Reprinted from [1], Copyright 1999, with permission from Elsevier)... 

In (+)-ionisation mode, a distinct selectivity of monoglucosides with respect to the formation of adduct ions was observed. Depending on the ring form (glucopyranoside or glucofuranoside) and the stereoisomerism (a- or (3-alkyl monoglucoside), a different affinity towards Na+ and... 

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