Sodium ion adduct

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). 

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. 

Sodium chloride may be added to the eluting solvent at a concentration of 0.01 M in order to accentuate sodium adduct ions in the MALDI-TOF mass spectrum and suppress the formation of potassium adduct ions. 

R. Orlando, C.A. Bush, C. Fenselau, Structural-analysis of oligosaccharides by MS-MS CID of sodium adduct ions, Biomed. Environ. Mass Spectrom., 19 (1990) 747. 

Lemoine J, Strecker G, Leroy Y, Foumet B, Ricart G. Collisional-activation tandem mass spectrometry of sodium adduct ions of methylated oligosaccharides sequence analysis and discrimination between alpha-NeuAc-(2-3) and alpha-NeuAc-(2-6) linkages. Carbohydr Res. 1991 221 209-17. 

Orlando R, Bush CA, Fenselau C. Structural-analysis of oligosaccharides by tandem mass-spectrometry — Collisional activation of sodium adduct ions. Biomed Environ Mass Spectrom. 1990 19 747-54. 

Because carotenes lack heteroatoms such as oxygen to which protons or sodium cations might attach, no ions are usually detected for these hydrocarbon compounds during ESI in positive mode, although protonated molecules and sodium adducts were observed for xanthophyUs under normal conditions with MeOH, MTBE, and H2O as a mobile phase from HPLC. Addition of a heptafluorobutanol oxidant at 0.1 or 0.5% produced abundant molecular ions of p-carotene with high reproducibility. Substitution of MeOH for acetonitrile produced similar limits of detection. ... 

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],... 

Positive ionisation is the method of choice for the detection of all nonionic surfactants generating molecular [M + H]+ or ammonium adduct ions ([M + NH4]+) in the presence of ammonium acetate. Often [M + Na]+ ions were also observed however, an excess of ammonium acetate will suppress their generation. While sensitivity in this mode is very high and can be improved by an excess of ammonium acetate to suppress sodium or potassium adduct ions, selectivity compared with negative ionisation for anionics is low. 

Using the same instrument with an ESI interface NPEOs and OPEOs show a great affinity for alkali metal ions. They gave exclusively, evenly spaced sodium adducts [M + Na]+, due to the ubiquity of sodium in the solvents and surfaces (Fig. 4.3.1(B)). In another type of instrument applying ESI, however, a relatively complicated spectrum was obtained (Fig. 4.3.2(A)), with similarities to the APCI spectrum of the first instrument. 

Although sodium adducts were preferably formed in both instruments, even in the absence of added electrolyte, in order to avoid the possible reduction in ionisation due to insufficient concentration of metal ions in solution, it is recommended that sample extracts are fortified with sodium ions prior to injection. However, the addition of higher concentrations can induce system instability and analyte suppression. Therefore, the concentration of added electrolyte should... 

Shang et al. [7] studied the effect of different additives (NaAc, NaOH, NaCl, NH4Ac) on analyte signal intensity and they found that the relative intensity of NPEO adduct ions may be enhanced by all additives, but NaAc produced the most abundant adduct ions for the entire ethoxylate series with good reproducibility. Additionally, the intensity of adducts, especially for mono- and diethoxylates was found to depend on reaction time prior to LC-ESI-MS analysis and concentration of NaAc. They recommended 0.5 mM NaAc for normal-phase separation with solvent system toluene-MeOH-water. In reversed-phase systems the highest abundance of sodium adducts for NPEOs ( iEO = 1-10) was observed at concentrations higher than 10 xM, while any further increase in concentration had very low influence on signal intensity [10,11],... 

In a similar study with ESI the influence of different buffers was studied [12]. In the presence of acetic acid (HAc) only in the MeOH/H20 mobile-phase, a mass spectrum resulted with ion adducts of Na and K appearing as the most abundant ones. However, minor peaks could also be observed in the mass spectrum resulting from ammonium adducts (Fig. 4.3.2(A)). The respective ions could be suppressed or enhanced by changing the nature of the buffer used in the mobile-phase. For example, when a potassium buffer was used, sodium and ammonium adducts were suppressed, and the spectrum became less complicated with primarily the potassium adduct ion being visible (Fig. 4.3.2(C)). In addition, the signal-to-noise ratio improved by about a factor of 1.5-2. Similarly, sodium or ammonium acetate buffers enhanced the sodium and ammonium adduct ions, meanwhile suppressing other adducts (Fig. 4.3.2(B) and (D), respectively). 

Simple molecular weight changes relative to the parent molecule may indicate the gain or loss of the equivalent of a methylene group (i.e. the loss of a methyl group replaced by a proton), oxidation, and hydration/dehydration or hydrolysis to list only a few possibihties. The formation of adduct ions, for example, sodium, potassium, or acetonitrile at +23, +39, and +43 Da, respectively, can provide the means for the preliminary identification of the molecular ion of a molecule. Isotope patterns, for example, from Cl, and even can also be diagnosti-... 

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