Rapid Communications in Mass Spectrometry

Zhang, Xiaotong; Wanigasekara, Eranda; Breitbach, Zachary S.; Dodbiba, Edra; Armstrong, Daniel W.

doi: 10.1002/rcm.4489pmid: 20306485

In previous studies, new electrospray ionization mass spectrometry (ESI‐MS) approaches were developed for the highly sensitive detection of singly and doubly charged anions in positive mode ESI‐MS by using specially synthesized dicationic and tricationic ion‐pairing agents, respectively. By detecting the positively charged ion complex in the positive mode, limits of detection (LODs) for the anions can be lowered by several magnitudes. In this work, we used eighteen newly synthesized tetracationic ion‐pairing agents, constructed with different geometries, linkages and cation moieties, for the detection of eighteen triply charged anions of different structural motifs. The LODs for these anions were from ten to several thousand times lower in the positive selective ion monitoring (SIM) mode than in the negative mode. These tetracationic agents also were shown to be useful for the detection of −1 and −2 anions. In addition, the LODs for −3 anions can be further lowered by monitoring the product fragments of the ion‐pairing complexes in the single reaction monitoring (SRM) mode. Copyright © 2010 John Wiley & Sons, Ltd.

Thomas, Andreas; Guddat, Sven; Kohler, Maxie; Krug, Oliver; Schänzer, Wilhelm; Petrou, Michael; Thevis, Mario

doi: 10.1002/rcm.4492pmid: 20301105

Occasionally, doping analysis has been recognized as a competitive challenge between cheating sportsmen and the analytical capabilities of testing laboratories. Both have made immense progress during the last decades, but obviously the athletes have the questionable benefit of frequently being able to switch to new, unknown and untested compounds to enhance their performance. Thus, as analytical counteraction and for effective drug testing, a complementary approach to classical targeted methods is required in order to implement a comprehensive screening procedure for known and unknown xenobiotics. The present study provides a new analytical strategy to circumvent the targeted character of classical doping controls without losing the required sensitivity and specificity. Using 50 µL of plasma only, the method potentially identifies illicit drugs in low ng/mL concentrations. Plasma provides the biological fluid with the circulating, unmodified xenobiotics; thus the identification of unknown compounds is facilitated. After a simple protein precipitation, liquid chromatographic separation and subsequent detection by means of high resolution/high accuracy orbitrap mass spectrometry, the procedure enables the determination of numerous compounds from different classes prohibited by the World Anti‐Doping Agency (WADA). A new hyphenated mass spectrometry technology was employed without precursor ion selection for higher collision energy dissociation (HCD) fragmentation experiments. Thus the mass spectra contained all the desired information to identify unknown substances retrospectively. The method was validated for 32 selected model compounds for qualitative purposes considering the parameters specificity, selectivity, limit of detection (<0.1–10 ng/mL), precision (9–28%), robustness, linearity, ion suppression and recovery (80–112%). In addition to the identification of unknown compounds, the plasma samples were simultaneously screened for known prohibited targets. Copyright © 2010 John Wiley & Sons, Ltd.

Chebbah, C.; Pozo, O. J.; Deventer, K.; Van Eenoo, P.; Delbeke, F. T.

doi: 10.1002/rcm.4499pmid: 20301101

An accurate and precise method for the quantification of 11‐nor‐Δ9‐tetrahydrocannabinol‐9‐carboxylic acid (THCA) in urine by liquid chromatography/tandem mass spectrometry (LC/MS/MS) for doping analysis purposes has been developed. The method involves the use of only 200 µL of urine and the use of D9‐THCA as internal standard. No extraction procedure is used. The urine samples are hydrolysed using sodium hydroxide and diluted with a mixture of methanol/glacial acetic acid (1:1). Chromatographic separation is achieved using a C8 column with gradient elution. All MS and MS/MS parameters were optimised in both positive and negative electrospray ionisation modes. For the identification and the quantification of THCA three product ions are monitored in both ionisation modes. The method is linear over the studied range (5–40 ng/mL), with satisfactory intra‐and inter‐assay precision, and the relative standard deviations (RSDs) are lower than 15%. Good accuracy is achieved with bias less than 10% at all levels tested. No significant matrix effects are observed. The selectivity and specificity are satisfactory, and no interferences are detected. The LC/MS/MS method was applied for the analysis of 48 real urine samples previously analysed with a routine gas chromatography/mass spectrometry (GC/MS) method. A good correlation between the two methods was obtained (r2 > 0.98) with a slope close to 1. Copyright © 2010 John Wiley & Sons, Ltd.

Taylor, Ivan F.; Blanksby, Stephen J.; Colbran, Stephen B.; Willett, Gary D.

doi: 10.1002/rcm.4493pmid: 20301108

High valent metal(IV)‐oxo species, [M(O)(MeIm)n(OAc)]+ (M = Mn–Ni, MeIm = 1‐methylimidazole, n = 1–2), which are relevant to biology and oxidative catalysis, were produced and isolated in gas‐phase reactions of the metal(II) precursor ions [M(MeIm)n(OAc)]+ (M = Mn–Zn, n = 1–3) with ozone. The precursor ions [M(MeIm)(OAc)]+ and [M(MeIm)2(OAc)]+ were generated via collision‐induced dissociation of the corresponding [M(MeIm)3(OAc)]+ ion. The dependence of ozone reactivity on metal and coordination number is discussed. Copyright © 2010 John Wiley & Sons, Ltd.

Perdian, D. C.; Cha, Sangwon; Oh, Jisun; Sakaguchi, Donald S.; Yeung, Edward S.; Lee, Young Jin

doi: 10.1002/rcm.4491pmid: 20301106

Mass spectrometric imaging has been utilized to localize individual astrocytes and to obtain cholesterol populations at the single‐cell level in laser desorption ionization (LDI) with colloidal silver. The silver ion adduct of membrane‐bound cholesterol was monitored to detect individual cells. Good correlation between mass spectrometric and optical images at different cell densities indicates the ability to perform single‐cell studies of cholesterol abundance. The feasibility of quantification is confirmed by the agreement between the LDI‐MS ion signals and the results from a traditional enzymatic fluorometric assay. We propose that this approach could be an effective tool to study chemical populations at the cellular level. Published in 2010 by John Wiley & Sons, Ltd.

Finiguerra, Alessandro; Spadafora, Antonia; Filadoro, Dina; Mazzuca, Silvia

doi: 10.1002/rcm.4494pmid: 20301104

Surface‐activated chemical ionization (SACI) has been widely used in recent years to analyze a range of different compounds (e.g., peptides, street drugs, amino acids). The main benefits of this technology are its high sensitivity and its effectiveness under different chromatographic conditions. Here, we used SACI in conjunction with a highly selective quadrupole time‐of‐flight mass analyzer to characterize a complex proteome pattern after separation by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE). The data obtained were compared with those obtained using the micro‐electrospray ionization (ESI) approach, which showed that using SACI strongly increased the number of detectable proteins. The higher sensitivity is mainly due to the ability of SACI to selectively produce singly charged species of high intensity under full‐scan conditions and doubly charged species for tandem mass spectrometric (MS/MS) peptide characterization by simply changing the ionization conditions during data acquisition. Copyright © 2010 John Wiley & Sons, Ltd.

Sánchez‐Guijo, Alberto; Montero, Olimpio

doi: 10.1002/rcm.4497pmid: 20301102

Mechanisms of retinol (ROL) transport in plasma alternative to that involving the Retinol‐Binding Protein (RBP) have been hypothesized after RBP‐knockout mice were shown to be viable and fertile. Accordingly, the possibility of a ROL fraction circulating free in plasma has been suggested. In this study, stable complex formation between ROL and the physiological relevant ions Na+, Li+, and K+ was investigated by using mass spectrometry and assessed in regard to the aforementioned alternative mechanism. The ROL‐Na complex was found to be kinetically favoured with respect to the ROL‐Li and ROL‐K complexes. Fragmentation of the [ROL‐Na]+ adduct rendered the carbocation [ROL+H–H2O]+ (m/z 269) and NaOH as neutral loss. In consonance with these results, it is hypothesized on the possibility of the complex [ROL‐Na]+ being an alternative way of ROL transport to cells, as well as an intermediate in cis/trans isomerism. Copyright © 2010 John Wiley & Sons, Ltd.

Jeckelmann, Nicolas; Haefliger, Olivier P.

doi: 10.1002/rcm.4500pmid: 20301100

Direct analysis in real time mass spectrometry (DART‐MS) was used to monitor the release kinetics of a taste‐refreshing compound from chewing gums into the saliva of subjects. A new DART‐MS sample probe was designed which was about four times more sensitive than the current benchmark probe. This decreased the impact of the dilution of the saliva samples that was required to minimize ion suppression effects and make quantitative analyses without an internal standard possible. The new probe was also about three times more reproducible, which allowed quantitative measurements to be conducted manually without requiring the enhanced precision provided by an automatic sample positioner. The accuracy of analyses performed by DART‐MS was verified by comparing the results obtained from saliva samples analyzed both by DART‐MS and by a more classical liquid chromatography/mass spectrometry (LC/MS) method. This investigation showed good agreement between the two techniques. DART‐MS could then be used to objectively demonstrate the efficiency of a granular carbohydrate‐based delivery system to boost for a few minutes the release of a lipophilic flavor raw material with a high octanol/water partition coefficient, cyclohexanecarboxamide, N‐ethyl‐5‐methyl‐2‐(1‐methylethyl) (WS‐3), from chewing gum into saliva. Copyright © 2010 John Wiley & Sons, Ltd.

Abate, Salvatore; Ahn, Yun Gyong; Kind, Tobias; Cataldi, Tommaso R. I.; Fiehn, Oliver

doi: 10.1002/rcm.4482pmid: 20301109

Many metabolomic applications use gas chromatography/mass spectrometry (GC/MS) under standard 70 eV electron ionization (EI) parameters. However, the abundance of molecular ions is often extremely low, impeding the calculation of elemental compositions for the identification of unknown compounds. On changing the beam‐steering voltage of the ion source, the relative abundances of molecular ions at 70 eV EI were increased up to ten‐fold for alkanes, fatty acid methyl esters and trimethylsilylated metabolites, concomitant with 2‐fold absolute increases in ion intensities. We have compared the abundance, mass accuracy and isotope ratio accuracy of molecular species in EI with those in chemical ionization (CI) with methane as reagent gas under high‐mass tuning. Thirty‐three peaks of a diverse set of trimethylsilylated metabolites were analyzed in triplicate, resulting in 342 ion species ([M+H]+, [M–CH3]+ for CI and [M]+., [M–CH3]+. for EI). On average, CI yielded 8‐fold more intense molecular species than EI. Using internal recalibration, average mass errors of 1.8 ± 1.6 mm/z units and isotope ratio errors of 2.3 ± 2.0% (A+1/A ratio) and 1.7 ± 1.8% (A+2/A ratio) were obtained. When constraining lists of calculated elemental compositions by chemical and heuristic rules using the Seven Golden Rules algorithm and PubChem queries, the correct formula was retrieved as top hit in 60% of the cases and within the top‐3 hits in 80% of the cases. Copyright © 2010 John Wiley & Sons, Ltd.

Wang, Siting; Song, Yan; Wang, Jiao; Ling, Xiaomei; Ge, Zemei; Li, Runtao; Cui, Jingrong

doi: 10.1002/rcm.4501pmid: 20301099

The zwitterionic drug 3‐methyl‐9‐(2‐oxa‐2λ5‐2H‐1,3,2‐oxazaphosphorine‐2‐cyclohexyl)‐3,6,9‐triazaspiro[5,5]undecane chloride (SLXM‐2) is a novel synthetic compound which has shown anticancer activity and low toxicity in vivo. In this study, the various gas‐phase fragmentation routes were analyzed by electrospray ionization mass spectrometry (positive ion mode) in conjunction with tandem mass spectrometry (ESI‐MSn) for the first time. In ESI‐MS the fragment ion at m/z 289 (base peak) was formed by loss of the chlorine anion from the zwitterionic precursor SLXM‐2. The fragment ion at m/z 232 was formed from the ion at m/z 289 by loss of 1‐methylaziridine. The detailed gas‐phase collision‐induced dissociation (CID) fragmentation mechanisms obtained from the various precursor ions extracted from the zwitterionic SLXM‐2 drug was obtained by tandem mass spectrometry analyses. Copyright © 2010 John Wiley & Sons, Ltd.