Electrospray negative mode

Ion source Electrospray, negative mode Mass transitions (optimized precursor and product ion mass to charge ratio) in negative ion mode Hyperforin 535 -> 383 m/z The instrument parameters have been optimized for the analysis of hyperforin. Both quadrupoles (Q1 and Q3) were operated in unit resolution. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

The qualitative determination of anionic surfactants in environmental samples such as water extracts by flow injection analysis coupled with MS (FIA-MS) applying a screening approach in the negative ionisation mode sometimes may be very effective. Using atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI), coupled with FIA or LC in combination with MS, anionic surfactants are either predominantly or sometimes exclusively ionised in the negative mode. Therefore, overview spectra obtained by FIA—MS(—) often are very clear and free from disturbing matrix components that are ionisable only in the positive mode. However, the advantage of clear... 

M [8]. Ferguson et al. [10] have shown that matrix effects may result in severe ion suppression in APEO analysis (this phenomenon occurs particularly in negative mode electrospray ionisation). They also demonstrated that the effect may be accounted for appropriately when using internal and surrogate standards, which closely mimic the ionisation behaviour of the analytes. In Ferguson s study, specially... 

Busman M., Schey K.L., Oatis Jr. J.E., and Knapp D.R.J. (1996), Identification of phosphorylation sites in phosphopeptides by positive and negative mode electrospray ionization tandem mass spectrometry, J. Am. Soc. Mass Spectrom. 7, 243-249. 

Fig. 1.13 Negative mode single quadrupole MS spectra of sulfuric acid monoester of 3-hydroxy retinoic acid (A) electrospray, (B) atmospheric pressure chemical ionization.

Unlike with GC-MS, quality criteria for identification of drug residues by LC-MS have not been yet defined within the European Union, but this is currently under review. Criteria for GC-MS stipulate the measurement of preferably at least four diagnostic ions. However, this is not always possible with LC-MS because most compounds will only produce an M ion in positive mode or a M ion in negative mode, with little fragmentation when using thermospray (TSP), electrospray (ESP), or atmospheric pressure chemical ionization (APCI). Even where the ions and ratios are in agreement, there will be still possibility of misidentification. For this reason, mass spectra data are often interpreted with additional supporting data such as the LC retention times, as, for example, in the LC-MS analysis of sulfadimethoxine and sulfadoxine that present identical mass spectra (24). 

Figure 4.19. Fragmentation mechanism for GSH in electrospray negative ion mode.

LC-MS/MS n/a operated in electrospray ionization positive and negative mode... 

Rodrigues Filho et al. studied the fragmentation of dipyridamole and several of its derivatives by electrospray ionization combined with collisional activated decomposition mass spectrometry in both positive and negative modes [61]. These compounds produce abundant mono-charged ions ([M + H]+) under electrospray ionization. Interpretation of the collisional activated decomposition spectra showed that fragmentation occurs preferentially in the ethanolamine groups attached at C-2, C-4, C-6, and C-8. 2-Methoxyethanol is eliminated when ethanolamines are in positions C-2/C-6, and 2-aziridinethanol is eliminated from... 

Detection electrospray (positive or negative mode), multiple reaction monitoring. 

Peak identification and interpretation of mass spectra Mobile phases for proanthocyanidins contain 2% (v/v) of acetic acid, and it suppresses electrospray ionization at negative mode. This can be overcome by adding ammonia acetate as an ionization enhancer. The ammonia acetate (lOmM in methanol, 0.1 mL/min flow rate) can be added into the flow via a three-way micro-splitter ( P-445, Upchurch Scientific, WA) just before the mass spectrometry. It can be delivered by a separate HPLC pump or by a syringe pump. 

A compromise solution for dereplication procedures is to use a combination of ionization modes. In one report (31), electrospray MS in both positive and negative modes was coupled to an HPLC interface and used to obtain information on unknown components of crude biologically active extracts. The authors of this report claimed successful identification of a known natural product in two out of eight biologically active extracts examined, another two compounds were identified as novel, and they assumed that the active components in the remaining four did not ionize or were present at a concentration below the limits of MS detection. 

Figure 7 ESI-MS studies of tetramolecular quadruplexes. The TG5T oligonucleotide was incubated in 0.15 M pH 7.0 ammonium acetate buffer for various amounts of time, then analysed by electrospray mass spectrometry (negative mode). From the initial peak corresponding to the TG5T single-strand (SS), one can see the gradual conversion to a quadruplex (G4), as well as the presence of dimeric (Di) and trimeric (Tri) species...

Analysis of acetochlor metabolites (ESA and OXA) in groundwater was carried out by reverse-phase liquid chromatography and detection by electrospray ionization/mass spectrometry (ESl/MS) in single ion monitoring and negative modes. 

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