Potassium adduct

The interpretation of the CVF spectra of the metabolites may be attempted by using a similar methodology to that described previously, i.e. subject to the cautionary note above, looking to see which ions occur at the same m /z values in the spectra of the parent drug and its metabolites and which show significant mass variations. The CVF spectrum from one of the metabolites is shown in Figure 5.52. In addition to the potassium adducts noted in the spectrum from... 

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. 

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). 

Despite these widespread applicahons, ILM is not equally well suited for all classes of analytes. Due to the need for increased laser energies/fluences for the ionizahon/desorption process, ILMs may only be of restricted suitability for some classes of analytes. For example for proteins, an extensive peak broadening caused potenhally by the combination of extended neutral losses (e.g., of ammonia or water) and alkali-ion-adduct formation can be observed. On the other hand, the increased tendency of the ILM to favor sodium and potassium adduct formation makes it ideally suited for the measurement of carbohydrates [38,40], whereas in proteomics, this tendency of adduct formahon is again an unwanted effect. 

Derivatized polyethers such as polyether sulfate have been investigated for both positive- and negative-ion calibration [11]. Although poly ether sulfates are not commercially available, they are easily synthesized. Lauryl sulfate ethoxy-lates were also used as calibrants for negative-ion ESI. Polyether amines and quaternary ammonium salts were used as positive-ion calibration solutions [11]. These commercially available compounds do not exhibit significant sodium or potassium adducts, and they are more easily flushed out of the mass spectrometer ion source than are nonderivatized polyethers. In addition, doubly charged poly ether diamines can produce reference peaks at low m/z values. 

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. 

Record MALDI mass spectra in positive ion mode. Look for proton, sodium, and potassium adduct ions in the range mJz 250 to 1000. Fragment ions caused by the loss of carbohydrate moieties are typical and can be diagnostic. 

If flavonol glycosides were eluted with excess sodium, potassium adduct ions will likely be suppressed, but there may be the formation of [M+2Na-H] ions. 

An adduct is an ion formed by direct combination of a neutral molecule and an ionizing ion other than the proton. In positive ion mode the most often observed is the sodium adduct, producing an ion with 22 mass units higher than the protonated molecule, that is (M + 23)+ instead of (M + 1)+. It is often accompanied by a potassium adduct, another 16 u higher ... 

The copper-catalyzed cross coupling reaction of thiophenol and aryl halide was also studied by ESl-MS. In this study, reported in 2011, three anionic complexes were assigned as key intermediates, Analysis of the same mixture by positive ion mode ESI revealed only the potassium adducts of thiophenol. An anionic... 

Ionic modifiers in the IPC eluent can provide a charge for neutral molecules so that they become detectable via the ESI interface. Conversely, counter ions reduce the charge state of an oppositely charged analyte or even convert it to the opposite polarity. If they are polycharged, for example, ESP and ESP modes were comparatively evaluated for the detection of nucleotides that are negatively charged. It was straightforward to use the ESP mode that detects the [M - H]"ion (with low levels of sodium and potassium adducts present), but ESP was a viable alternative because the volatile N,N-dimethylhexylamine IPR yields ion-pairs with the nucleotides. The most abundant relevant ion was the adduct between the compound and... 

Halogenated aiyloxyphenoxypropionic acids are a new class of herbicides used for the selective removal of grass species. In commercial preparations, they are present as alkyl esters. In negative-ion ESI, haloxifop, fluazifop, and diclofop all show similar behaviour. The deprotonated molecule is the base peak in the spectrum. Weak formate and acetate adducts occur, and a fragment due to the loss of the propionate part [45]. The analysis of fluazifop and its butyl ester, fenoxaprop, quizalofop and haloxyfop and their ethyl esters, and diclofop and its methyl ester was reported. The free acids were analysed in negative-ion mode, and the esters in positive-ion mode. The esters showed sodium and potassium adducts next to the protonated molecules. The adduct formation was suppressed by the addition of 25 mmol/1 formic acid to the mobile phase. The influence of the orifice potential on the appearance of their mass spectra was studied [46-47]... 

These alkynes do not undergo such smooth dimerizations to alkadiene derivatives such as 21 or 22 when sodium or potassium is employed or when the reaction is conducted in other solvents (27-30). The potassium adduct of tert-butylphenylacetylene (cf. 13) dimerizes through the para-position of the phenyl group (35). These observations indicate that the special reactivity of lithium may reside in the greater autoassociation tendency of its radical-anion adducts (20a). 

The number of adduct ions observed in an ES mass spectrum seems to increase when more unusual solvent mixtures are being used in combination with ES. Apart from the usual protonated, sodium and potassium adduct ions observed in positive ion mode, and the deprotonated and chlorine adduct ions in the negative ion mode, others may well be observed. When interpreting mass spectra, the presence of adduct ions may be considered either a challenge or a nuisance, depending on the mood of the analyst ... 

Singly charged ions encompass radical ions, protonated/deprotonated molecules, products of alkali ion additions, or complex ions with other charge carriers. In the case of singly charged radical ions, the molecular weight of an analyte molecule approximately equals to the m/z value of that ion (one electron affects the measurement by only 0.00055 u). In the case of protonated or deprotonated molecules, the m/z values are expressed as m -I- 1 or m - 1, respectively. Alkali metal adducts are also commonly observed in MS for example, m -l- 23 (sodium adducts) or m -i- 39 (potassium adducts). The alkali ions are mostly contaminants, which are very difficult to remove from sample vials, solvents, or sample plates. However, some analytes such as carbohydrates can only be ionized by association with alkali ions [5,6]. 

TATP + Na]+ or [TATP + K]" were not produced as has been previously reported for the analysis of TATP by ESI-MS and desorption electrospray ionization (DESI) [50,51]. A [TATP + H]" ion was also not observed by LEMS however, the sodium and potassium adduct ions of the TATP dimmer at m/z 467 [2TATP + Na]+ and m/z 483 [2TATP + K]", respectively, were observed [54],... 

The mass spectra of materials containing many chemical components generally show a large number of peaks, rendering unambiguous identifications difficult. Further complications are added by fragmentation reactions, or in-source recombination of ions and neutrals to form higher mass species. Typical examples include the formation of sodium and potassium adducts. 

In positive ion mode, phosphopeptides form strong sodium and potassium adducts, which often give more intense signals than the parent ion. Peptides containing multiple phosphorylation sites often give better spectra if recorded in negative ion mode. 

Distilled and deionized water must be used in the HPLC solvents for LC-MS analysis to avoid the production of sodium or potassium adducts. 

Figure 19 Analysis of oligonucleotides by LC-MS using a Cia reversed-phase stationary phase and a gradient from lOOmM triethylammonium acetate, pH 7/ acetonitrile to 400 mM hexafluoro-2-propanol/methanol at 0.2mL/min (column 2.1 X 250 mm). The upper panel shows an ESI spectrum acquired on line of a 15-mer, and the lower trace represents the chromatogram (TIC) acquired during the LC-MS run. Deconvolution of the spectrum allows discrimination between the free 15-mer and its sodium and potassium adducts. (From Ref. 17.)...

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