A new approach of volatile compounds analysis is proposed using a linear ion trap Orbitrap mass spectrometer coupledwith gas chromatography through an atmospheric pressure photoionization interface. In the proposed GC-HRMS/MSapproach, direct chemical composition analysis is made for the precursor ions in high resolution MS spectra and the structuralidentifications were made through the database search of high quality MS/MS spectra. Successful analysis of a complex perfumesample was demonstrated and compared with GC-EI-Q and GC-EI-TOF. The current approach is complementary to conventionalGC-EI-MS analysis and can identify low abundance co-eluting compounds. Toluene co-sprayed as a dopant through APIprobe significantly enhanced ionization of certain compounds and reduced oxidation during the ionization.
Phosphorylation and glycosylation are two of the most important and widespread post-translational modifications(PTMs) in an organism. Proteomics analysis of the PTMs has been challenged by low stoichiometry of the modified proteins andsuppression effects by high abundance proteins, typically no-functional house-keeping proteins. In this study, a novel methodwas applied for not only isolating PTM peptides from intact peptides but also concurrently characterizing of glyco- and phosphoproteomeusing electrostatic repulsion hydrophilic interaction chromatography (ERLIC) packed with silica coated by crosslinkedpolyethyleneimine. For 2 mg tryptic digest of mouse proteome of epicardial adipose tissue with fat diet, 802 N-glycosylatedpeptides of 316 glycoproteins and 159 phosphorylated peptides of 75 phosphoproteins were identified using HPLC chip/quadrupole time-of-flight (Q-TOF) tandem mass spectrometer.
In this study, comprehensive two dimension gas chromatography (2D GC-MS) and 15 T Fourier transform ion cyclotronresonance mass spectrometry (15T FT-ICR MS) connected to atmospheric pressure photo ionization (APPI) have beencombined to obtain detailed chemical composition of a diesel oil sample. With 2D GC-MS, compounds with aliphatic alkyl, saturatedcyclic ring(s), and one aromatic ring structures were mainly identified. Sensitivity toward aromatic compounds with morethan two aromatic rings was low with 2D GC-MS. In contrast, aromatic compounds containing up to four benzene rings wereidentified by APPI FT-ICR MS. Relatively smaller abundance of cyclic ring compounds were found but no aliphatic alkyl compoundswere observed by APPI FT-ICR MS. The data presented in this study clearly shows that 2D GC-MS and 15T FT-ICRMS provides different aspect of an oil sample and hence they have to be considered as complementary techniques to each otherfor more complete understanding of oil samples.
Myoglobin was hydrolyzed by microwave-assisted weak acid hydrolysis with 2% formic acid at 37 oC, 50 oC, and100 oC for 1 h. The most effective hydrolysis was observed at 100 oC. Hydrolysis products were investigated using matrixassistedlaser desorption/ionization time-of-flight mass spectrometry. Most cleavages predominantly occurred at the C-termini ofaspartyl residues. For comparison, weak acid hydrolysis was also performed in boiling water for 20, 40, 60, and 120 min. A 60-min weak acid hydrolysis in boiling water yielded similar results as a 60-min microwave-assisted weak acid hydrolysis at100 oC. These results strongly suggest that microwave irradiation has no notable enhancement effect on acid hydrolysis of proteinsand that temperature is the major factor that determines the effectiveness of weak acid hydrolysis.
After success of sildenafil for the treatment of erectile dysfunction, a large number of its analogues have beenapproved from FDA. Recently, the illegal dietary supplements which include sildenafil, vardenafil, tadalafil, or analogues ofthese drugs as ingredient have been widely distributed. Therefore, the determination of the residue of synthetic phosphodiesterase-5 (PDE-5) inhibitors in dietary supplements is highly required due to indiscriminate and unintentional overdose causednausea, chest pains, fainting and irregular heartbeat. In this paper, we report a rapid and sensitive analytical method for thesimultaneous determination of nine phosphodiesterase-5 inhibitors by liquid chromatography-high resolution mass spectrometry. The present method was found to be accurate and reproducible with 40 μg/g of the limit of quantification for the nine PDE-5inhibitors. The developed method can be successfully applied to the analysis of the seven illegal dietary supplements.
Mass spectrometric analysis was carried out using multicollector inductively coupled plasma mass spectrometry(MC-ICP-MS) for the precise and accurate determination of the isotope ratios of ultratrace levels of uranium dissolved in 3%HNO3. We used the certified reference material (CRM) 112-A at a trace level of 100 pg/mL for the uranium isotopic measurement. Multiple collectors were utilized for the simultaneous measurement of uranium isotopes to reduce the signal uncertaintydue to variations in the ion beam intensity over time. Mass bias correction was applied to the measured U isotopes to improve theprecision and accuracy. Furthermore, elemental standard solution with certified values of platinum, iridium, gold, and thalliumdissolved in 3% HNO3 were analyzed to investigate the formation rates of the polyatomic ions of Ir40Ar+, Pt40Ar+, Tl40Ar+,Au40Ar+ for the concentration range of 50–400 pg/mL. Those polyatomic ions have mass-to-charge ratios in the 230–245 m/zregion that it would contribute to the increase of background intensity of uranium, thorium, plutonium, and americium isotopes. The effect of the polyatomic ion interference on uranium isotope measurement has been estimated.
A method based on flow injection-isotope dilution-cold vapor-inductively coupled plasma mass spectrometry (FI-IDCV-ICP/MS) has been applied to determine trace level of mercury in fly ash. 200Hg isotopic spike was added to 0.25 g of BCR176Rfly ash and then decomposed by microwave digestion procedure with acid mixture A (8 mL HNO3 + 2 mLHCl + 2 mL HF) and acid mixture B (8 mL HNO3 + 2 mL HClO4 + 2 mL HF) for applying IDMS. Mercury cold vapor was generatedby using reductant solution of 0.2% (w/w) NaBH4 and 0.05% (w/w) NaOH. The measurements of n(200Hg)/n(202Hg) isotoperatio was made using a quadrupole ICP/MS system. The accuracy in this method was verified by the analysis of certified referencematerial (CRM) of fly ash (BCR 176R). The indicative value of Hg in BCR 176R fly ash was 1.60 ± 0.23 mg/kg (k = 2). The determinedvalues of Hg in BCR 176R fly ash by the method of FI-CV-ID-ICP/MS described in this paper were 1.60 ± 0.24 mg/kg(k = 3.18) and the analysis results were in well agreement with the indicative value within the range of uncertainty.