Ammonium acetate infusion

A rapid technique for the identification of surfactants in consumer products by ESI-MS was proposed by Ogura and co-workers [6], After a simple preparation procedure, infusion of the sample, which was prepared in a water/methanol mixture (50 50) containing 10 mM ammonium acetate, allowed assignment of the [M + NH4]+ ions of Cio- and Ci2-mono- and -diglucoside in the mass spectrum (ion masses as in Table 2.7.1). The approach even permitted quantitative analysis when deuterated internal standards were used. 

Different organic and inorganic buffers, such as ammonium acetate, ammonium formate, HEPES, Gly-Gly, and triethanolamine, were selected to study the response of biotin and fluorescein-biotin in MS and compared to phosphate buffer. Biotin and fluorescein-biotin were dissolved in the carrier solution compositions of buffer (10 mM pH 7.5)/methanol (50 50, v/v) at concentrations of 10 ng pl k Both infusion and 20 pl-loop injection experiments were performed with detection by MS in full-scan and SIM mode. Main optimization criteria are the maximum response of biotin and fluorescein-biotin with lowest interference of the carrier solution. HEPES, Gly-Gly, and triethanolamine give very high background response, which significantly hampers the detection of biotin and fluorescein-... 

The decision tree and infusion tuning experiments used in the systematic method development for choosing the mobile phase to achieve the best sensitivity in LC-MS/MS and reducing the matrix effect are shown in Figures 8.1 to 8.3. The run time was 3.5 min using 96.5 3.5 acetonitrile/1 mM ammonium acetate as mobile phase. Only the peaks of interest were collected all the rest were... 

The MS and MS/MS behaviors of the four corticosteroids under positive ion ESI was investigated using direct infusion of standard solutions into the mass spectrometer. In preliminary experiments, it was observed that all four corticosteroids formed strong [M+Na]+and [M+K]+ ions along with relatively weaker [M+H]+ ions in methanol/acetonitrile/water. However, an acidic 2 mM ammonium acetate buffer... 

Figure 7. Negative Ion Electrospray Scan of Oligo-thymidiUic Acid PCR Primer (10 mer) Before and After Microcon-SCX. A. (Top) ES Scan of 10 picomoles of oligonucleotide in 20 mM sodium acetate, pH 5- (Lower) ES Scan after 10 picomoles of primer was passed over Microcon-SCX, desorbed and vacuum dried. Samples were reconstituted in water and diluted to 10 mM TEA in 50 % IPA and infused at a rate of 2 ml/min (Micro Mass). The majority of [Na" "] passed through membrane and was removed following Microcon-SCX treatment A 20 mM ammonium acetate or 10 mM HCl/ 20% MeOH wash removed remaning [Na from sample.

Figure 5.19 Effect of HPLC injections on the APCI signal from the analyte infused post-column at a constant rate the isocratic mobile phase was 80 % acetonitrile and 20 % aqueous ammonium acetate (1 % w/v), and the analyte solution that was infused postcolumn was 1 p.g.mL in the mobile phase, (a) Infusion of parent compound with no injection on the HPLC (mobile phase only) (b) enhancement effect of injection of water on the signal from infused analyte (c) suppression effect of injection of extract of a blank plasma sample on the signal from the infused analyte (see Section 5.3.5a). The diagonal line is drawn to connect the injection times in the different chromatograms. Reproduced from Sangster (2004), Rapid Commun. Mass Spectrom. 18, 1361, with permission of John Wiley Sons, Ltd.

In addition to the analysis of TATP, the synthetic impurities (i.e., oligomeric peroxides) are also observed by APCI. Figure 16.7 contains the APCI spectra, positive ion mode, from direct infusion of an HCl-catalyzedTATP synthetic product mixture. The sample was infused as a solution in methanol with ammonium acetate additive. The m/z 240 ion corresponds to [TATP + and the series of ions separated by 74 Da, m/z 422-866, correspond to [H(00C(CH3)2) 00H + NH4] (n = 5-11) [60]. Experimental parameters for direct infusion APCI analysis of TATP are given in Table 16.2. 

Prepare the solution for ESI MS analysis by dissolving the sample in a mixture of 80% (v/v) acetonitrile and 20% (v/v) 0.25 mM ammonium acetate in water. Deliver the sample solution (100 pM) from a syringe to the ESI source at a flow rate of 6 pL/min using the continuous infusion method. 

Detergents and salts interfere with protein molecular weight determinations, so proteins should be isolated to homogeneity in a volatile buffer system. Ideally, proteins are desalted by reverse-phase HPLC in aqueous acetonitrile or methanol solutions. These solvents can be infused directly into the mass spectrometer. Alternatively, proteins can be lyophilized from ammonium bicarbonate, ammonium acetate, or N-ethyl morpholine solutions. 

Figure 18 Negative ESI mass spectrometry of two 40-mer oligonucleotides without (a) and with prior treatment with ammonium acetate to replace alkali metal ions (b). Replacement of metal cations with ammonium ions results in a significant improvement in both mass accuracy and resolution. The signal at m/z 849.2 corresponds to the internal standard that was infused simultaneously. (From Ref. 79.)...

Figure 4.2 Representative positive- and negative-ion ESI mass spectra acquired under weak acidic, neutral, and weak basic conditions. A lipid extract of mouse spinal cord at 48 days was prepared and mass spectrometric analysis was performed [26]. Positive- and negative-ion ESI mass spectra as indicated were acquired after direct infusion in the presence of 0.5% acetic acid (a and b), 5 mM ammonium acetate (c and d), and 10 pM lithium hydroxide (e and f) in the infused solution. IS, pPE, and ST stand for internal standard, plasmenylethanolamine, and sulfatide, respectively.

Figure 7.2 Product-ion ESI-MS spectra of 16 0-18 1 phosphatidylcholine acetate adduct after CID at different collision energy. Product-ion ESI-MS analysis of acetate adduct of 16 0-18 1 dPC at 2/z 818.5 in the presence of ammonium acetate in the infusion solution was performed on a Thermo Fisher TSQ Vantage mass spectrometer. Collision activation was performed at collision energy of 15 (a), 20 (b), 25 (c), and 30 (d) eV, and gas pressnre of 1 mTorr. Ac stands for acetate. These resnlts demonstrate two key points. First, while product-ion mass spectra acquired at different collision energy are very different, the fragmentation pattern of dPC species is identical under different experimental conditions. Second, the low-mass fragment ions increase as collision energy.

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