Direct determination of dialkyl phosphates by strong anion-exchange liquid chromatography/atmospheric pressure chemical ionization mass spectrometry using a quadrupole ion trap instrument

The direct determination of dialkyl phosphates (DAPs) in water by strong anion-exchange (SAX) liquid chromatography/atmospheric pressure chemical ionization (APCI) mass spectrometry was investigated. The SAX high-performance liquid chromatography (HPLC) column was eluted with methanol/water gradients containing ammonium formate (AF) separating the DAPs which included six dimethyl- and diethyl-substituted phosphates, thiophosphates, and dithiophosphates. The high buffer concentrations required for separation were compatible with -ve APCI, but in +ve APCI the DAPs were unstable giving anomalous ions such as [M+15]+ and [M+29]+. These ions are believed to result from ion molecule reactions with CH3OH2+ in the plasma. DAPs are very stable in -ve APCI being detected as abundant [M-H](-) ions, even with 200 mM AF. At higher AF concentration formate clusters ([M+45](-) and [M+91](-)) were seen. Fragmentation by collision-activated dissociation (CAD) was more efficient for deprotonated ethyl-substituted DAPs which lost ethylene followed by ethanol. APCI instrument detection limits were in the low ng/mL range and the response was highly linear. Isotope dilution quantitation using d10-diethyl dithiophosphate (DEDTP) as an internal standard produced an instrument detection limit of 2 ng DEDTP/mL and method detection limit (MDL) of 9.3 ng/mL with accuracy of 99% (spike concentration, 25 ng/mL). DAP mixtures required storage in cold, dry conditions and alcohol solvents should be avoided because of solvolysis reactions.     

Application of liquid chromatography-atmospheric pressure chemical ionization mass spectrometry to the differentiation of stereoisomeric C19-norditerpenoid alkaloids

High-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS) was successfully applied to stereoisomeric C19-norditerpenoid alkaloids at position 1. APCI-MS allowed the easy and precise control of the energy deposition by varying the drift voltage. Comparison of the breakdown curves, observed by changing the potential difference between the first electrode and the second electrode of the APCI ion source, revealed stereochemical dependence of different fragmentations. The APCI spectra of alkaloids were predominantly the [M+H]+ ion and major fragment ion, corresponding to the [M+H-H2O]+ ion or the [M+H-CH3COOH]+ ion, and comparison of the spectra showed that the abundance of fragment ions was significantly higher for C-1 beta-form alkaloids than for C-1 alpha-form alkaloids. The characteristic fragment ions were formed by the loss of a water, acetic acid or methanol molecule at position 8. The fragmentation mechanisms depending on the stereochemistry of the precursor ion could be discerned by recording the spectra in a deuterated solvent system of 0.05 M ammonium acetate in D2O-acetonitrile-tetrahydrofuran. Loss of D2O from the precursor ion gave the fragment ion. This result indicated that the proton of protonation was included in the leaving water molecule. The peak intensity ratio R=[M+H]+/[M+H-H2O]+ manifested the stereochemical differentiation of alkaloids at position 1.     

Application of liquid chromatography-atmospheric pressure chemical ionization mass spectrometry to the differentiation of stereoisomeric diterpenoid alkaloids

High-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS) was successfully applied to seven stereoisomeric diterpenoid alkaloids at position 1 or 12. Comparison of the breakdown curves, observed by changing the potential difference between the first electrode and the second electrode of the APCI ion source, revealed stereochemical dependence of different fragmentations. The APCI spectra of alkaloids were predominantly the [M+H]+ ion and the major fragment ion, corresponding to the [M+H-H2O]+ ion or the [M+H-CH3COOH]+ ion, and comparison of the APCI spectra showed that the abundance of fragment ions was significantly higher for C-1 beta-form alkaloids than for C-1 alpha-form alkaloids, and for C-12 beta-form alkaloids than for C-12 alpha-form alkaloids. The characteristic fragment ions were formed due to the loss of an acetic acid or a water molecule at position 12. The fragmentation mechanisms depending on the stereochemistry of the precursor ion could be discerned by recording the spectra in a deuterated solvent system of 0.05 M ammonium acetate in D2O-acetonitrile-tetrahydrofuran. Loss of CH3COOD or D2O from the precursor ion gave the fragment ion. This result indicated that the proton of protonation was included in the leaving acetic acid and water molecule, respectively. The peak intensity ratio for R=[M+H]+/[M+ H-H2O]+ + [M + H-CH3COOH] + manifested the stereochemical differentiation of alkaloids at position 1 or 12.     

Investigations of taxoids by electrospray and atmospheric pressure chemical ionization with tandem mass spectrometry

The fragmentation behavior of taxoids was studied using electrospray (ESI) and atmospheric pressure chemical ionization (APCI) sources with multi-stage tandem mass spectrometry. In the positive ion mode taxoids gave prominent [M+Na]+ and [M+K]+ ions with the ESI source, and [M+NH4]+ or [M+H]+ ions with the APCI source. The MS/MS fragmentations of ions produced by APCI and ESI sources were very similar. For both sources, the presence of cinnamoyl or benzoyl groups could be characterized by initial losses of 148 or 122 u, respectively, from molecular adduct ions. However, the elimination of cinnamic acid was relatively difficult for the molecular adduct ions formed by APCI, and was comparable in importance to the loss of acetic acid. The other fragments involved losses of CH2CO, CO, and H2O. The 5/7/6 type taxoids underwent characteristic losses of 58 or 118 u from ions produced by both APCI and ESI sources. The fragmentation behavior was remarkably influenced by substitution locations. The elimination of the C-10 benzoyl group was usually the first fragmentation step, while that of the C-2 benzoyl group was relatively difficult. The acetoxyl group at C-7 was more active than those at C-2, C-9, and C-10, which in turn were more active than that at C-4. These fragmentation rules could facilitate the rapid screening and structural characterization of taxoids in plant extracts by high-performance liquid chromatography/mass spectrometry (HPLC/MS).     

Detection of 6-(methylsulfinyl)hexyl isothiocyanate (6-MITC) and its conjugate with N-acetyl-L-cysteine (NAC) by high performance liquid chromatograpy-atmospheric pressure chemical ionization mass spectrometry (HPLC-MS/APCI)

A method using high-performance liquid chromatography (HPLC) and atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) was established for the detection of 6-(methylsulfinyl)hexyl isothiocyanate (6-MITC) and its conjugate with N-acetyl-L-cysteine (NAC). The optimal chromatographic conditions were obtained on an ODS column (150 x 4.6 mm, 3 microm) with the column temperature at 37 degrees C. The mobile phase consisted of a methanol-0.1% trifluoroacetic acid (TFA) mixture (50 : 50, v/v), and the flow rate was 0.3 ml/min. The detection wavelength was set at 220 nm. The identities of the peaks were accomplished by comparing retention times (tR), UV and mass data. All calibration curves showed good linear regression (correlation coefficients for 6-MITC and NAC>0.999) within test ranges. The developed method provided satisfactory precision calculated as percent coefficient of variation with overall intra-day and inter-day variations of less than 5% (4.1 and 4.9% for 6-MITC; 4.2 and 4.9% for NAC). Both 6-MITC and NAC had good responses in the positive APCI and formed strong [M+H]+ ions in the full scan spectra at an m/z of 206 and 164, respectively. The presence of the [M+H]+ ion for the 6-MITC/NAC conjugate was also observed at an m/z of 369. To our best knowledge, this is the first report that describes the formation of the 6-MITC/NAC conjugate and its detection method by HPLC-MS.     

Electrospray and atmospheric pressure chemical ionization tandem mass spectrometric behavior of eight anabolic steroid glucuronides

Mass spectrometric and tandem mass spectrometric behavior of eight anabolic steroid glucuronides were examined using electrospray (ESI) and atmospheric pressure chemical ionization (APCI) in negative and positive ion mode. The objective was to elucidate the most suitable ionization method to produce intense structure specific product ions and to examine the possibilities of distinguishing between isomeric steroid glucuronides. The analytes were glucuronide conjugates of testosterone (TG), epitestosterone (ETG), nandrolone (NG), androsterone (AG), 5alpha-estran-3alpha-ol-17-one (5alpha-NG), 5beta-estran-3alpha-ol-17-one (5beta-NG), 17alpha-methyl-5alpha-androstane-3alpha,17beta-diol (5alpha-MTG), and 17alpha-methyl-5beta-androstane-3alpha,17beta-diol (5beta-MTG), the last four being new compounds synthesized with enzyme-assisted method in our laboratory. High proton affinity of the 4-ene-3-one system in the steroid structure favored the formation of protonated molecule [M + H]+ in positive ion mode mass spectrometry (MS), whereas the steroid glucuronides with lower proton affinities were detected mainly as ammonium adducts [M + NH4]+. The only ion produced in negative ion mode mass spectrometry was a very intense and stable deprotonated molecule [M - H]- . Positive ion ESI and APCI MS/MS spectra showed abundant and structure specific product ions [M + H - Glu]+, [M + H - Glu - H2O]+, and [M + H - Glu - 2H2O]+ of protonated molecules and corresponding ions of the ammonium adduct ions. The ratio of the relative abundances of these ions and the stability of the precursor ion provided distinction of 5alpha-NG and 5beta-NG isomers and TG and ETG isomers. Corresponding diagnostic ions were only minor peaks in negative ion MS/MS spectra. It was shown that positive ion ESI MS/MS is the most promising method for further development of LC-MS methods for anabolic steroid glucuronides.     

Mass spectral studies on aryl-substituted N-carbamoyl/N-thiocarbamoyl narcotine and related compounds

Positive ion mass spectral fragmentation of new N-carbamoyl/N-thiocarbamoyl derivatives of narcotine and compounds closely related to it are reported and discussed. The techniques used include electron impact (EI), fast-atom bombardment (FAB), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). Prominent peaks in the mass spectra of these compounds appear to involve C-C bond cleavage beta to the amine nitrogen with loss of the 4,5-dimethoxy(1H)isobenzofuranone moiety from their molecular ions, along with another prominent peak at m/z 382. No molecular ion peaks of these compounds were recorded in EI, whereas intense [M + H]+ ion peaks were observed in FAB and ESI spectra. MALDI also yielded [M + H]+ ion peaks in good agreement with FAB and ESI studies.     

Evaluation of different quantitative approaches for the determination of noneasily ionizable molecules by different atmospheric pressure interfaces used in liquid chromatography tandem mass spectrometry: Abamectin as case of study

The liquid chromatography tandem mass spectroscopy residue determination of compounds without any acidic or basic centers such as abamectin has been investigated. Several approaches regarding the interface used and adduct formation have been compared. The low acidity of the hydroxyl groups only made deprotonation feasible using the atmospheric pressure chemical ionization (APCI) interface. To obtain sufficient sensitivity for residue analysis, the Ion Sabre APCI interface was necessary. However, the sensitivity attained was lower than for monitoring adducts in positive ion mode. Using electrospray ionization, different adducts with Na+, NH4+, and Li+ were tested and compared. The best results were obtained for the ammoniated adduct in electrospray ionization (ESI) because of its high sensitivity and the presence of several product ions with similar abundance. The highest sensitivity was reached using an in-source fragment as precursor ion, leading to a limit of detection (LOD) of 2 microg/L with low relative standard deviation. The relatively high abundance of other transitions allowed abamectin confirmation at concentrations close to the LOD (6 microg/L). Alkali ions were found to be a suitable alternative to determine and confirm abamectin at residue levels. The [M + Na]+ also presented various product ions with similar abundance, which allowed confirmation at LOD levels. However, this LOD was found to be almost four times higher than with [M + NH4]+ because of the poor sensitivity of the transitions obtained. Although the use of Li+ facilitated the fragmentation of the adduct [M + Li]+, with similar sensitivity to [M + NH4]+, this fragmentation preferentially generated only one product ion, which did not allow confirmation at concentration levels lower than 15 microg/L. The use of APCI for monitoring adducts was also feasible, but with less sensitivity. The sensitivity increased with the Ion Sabre APCI, although it was still five times lower than with ESI. Other adduct formers such as Co2+ and Ni2+ also were tested with unsatisfactory results.     

High performance liquid chromatography-mass spectrometry analysis of protoberberine alkaloids in medicine herbs

RP-HPLC is the main method for the analysis of alkaloids. However, peak tailing is a problem that commonly occurs in the separation of alkaloids. In order to overcome this, three kinds of RP columns were compared for the analysis of protoberberine alkaloids in Coptidis Rhizoma and Phellodendri Cortex in this work. XTerra MS C18 column was the best one which gave the best symmetry factor under the same conditions. With this column, a good separation of the crude extracts of C. Rhizoma and P. Cortex was achieved using 0.1% v/v formic acid buffer and methanol as mobile phase. At the same time, the crude extracts of C. Rhizoma and P. Cortex were analyzed by the LC-ESI-MSn and LC-atmospheric pressure chemical ionization (APCI)-MSn methods. In the analysis of HPLC-ESI/MSn, structures of five protoberberine alkaloids were elucidated, compared to authentic standards, and data from the literature. At the same time, the structure of a novel compound was elucidated. In the HPLC-APCI/ MSn analysis, there was an interesting phenomenon that the relative abundance of the ions M+ and [M + 2]+ was different for different alkaloids. The possible fragmentation pathways of protoberberine alkaloids in APCI/MS analysis were studied for the first time in the present work.     

The detection of red pigment-concentrating hormone (RPCH) in crustacean eyestalk tissues using matrix-assisted laser desorption/ionization-Fourier transform mass spectrometry: [M + Na]+ ion formation in dried droplet tissue preparations

Red pigment-concentrating hormone (RPCH), an octapeptide found in crustaceans and insects with the sequence pGlu-Leu-Asn-Phe-Ser-Pro-Gly-Trp-NH2, is an N- and C-terminally blocked uncharged peptide. These structural features are shared with many members of the larger adipokinetic hormone (AKH)/RPCH peptide family in insects. We have applied vacuum UV matrix-assisted laser desorption/ionization (MALDI)-Fourier transform ion cyclotron mass spectrometry (FTMS) to the direct analysis of crustacean sinus gland tissues, using 2,5-dihydroxybenzoic acid (DHB) as the MALDI matrix, and have found that RPCH is detected in the cationized, [M + Na]+, form under conditions where other peptides in the direct tissue spectra are protonated without accompanying [M + Na]+ or [M + K]+ satellite peaks. The [M + H]+ ion for RPCH is not detected in tissue samples or for an RPCH standard, even when care is taken to eliminate metal ions. This behavior is not unprecedented; however, both direct tissue spectra and SORI-CID spectra provide no clues to suggest that the ionizing agent is a metal cation. In this communication, we characterize the MALDI-FTMS ionization and SORI-CID mass spectra of the [M + Na]+ and [M + K]+ ions from RPCH, and report on the detection of this neuropeptide in sinus gland tissues from the lobster Homarus americanus and the kelp crab Pugettia producta. We describe two strategies, an on-probe extraction procedure and a salt-doping approach, that can be applied to previously analyzed MALDI tissue samples to enhance and unmask sodiated peptides that may otherwise be mistaken for novel neuropeptides.     

Ion trap mass spectrometry of trimethylsilylamides following gas chromatography

Fatty acid amides are a class of compounds with newly discovered biological activity. The ion trap mass spectrometric characteristics of silylated fatty acid amides were examined. Silylation of primary fatty acid amides is required prior to gas chromatography owing to thermal instability of the underivatized compound. The trimethylsilylated amides do not yield a molecular ion under normal electron ionization conditions (70 eV). With methane as a chemical ionization gas, the [M+H]+ ion appears. The [M+H]+ ion also appears when the helium buffer gas pressure is increased in the ion trap. There are three fragments other than the [M+H]+ peak that are predominant in the ion trap mass spectra of these compounds. Two of the fragments have been reported previously, namely the m/z 59 and the [M-71]+ fragments. The fragment of m/z 72 was identified and is the result of a rearrangement. Isotopic labeling was used to confirm fragment identity and the composition of the rearrangement products. Fragmentation patterns were affected by the amide chain length and concentration.     

Influence of solvent and counter ion on copper complexes with N-alkyl-pyridine-2-carboxamides as studied by electrospray ionization mass spectrometry

The interactions of copper(II) with N-alkyl-pyridine-2-carboxamides (M) were studied by electrospray ionization mass spectrometry. The influence of solvent and counter ion (Cl-, ClO4-) on the type of ions (complexes) observed was discussed. By cone voltage increase, the fragmentation "in source" of the ions discussed was achieved. In methanol solution containing N-alkyl-pyridine-2-carboxamide (M) and CuCl2 the singly- and doubly charged-ions [M+CuCl]+ and [M2+Cu]+2 were detected. In acetonitrile solution containing N-alkyl-pyridine-2-carboxamide and CuCl2, the copper(I)-containing ions [M+CH3CN+Cu]+ were formed. The use of Cu(ClO4)2 instead of CuCl2 resulted in more abundant doubly-charged ions in both methanol and acetonitrlile solutions and, for the former solution, the ions containing methoxyl anion, namely [M+CuOCH3]+, were observed. When water was used as a solvent, the abundant ions corresponding to the protonated ligands were formed, while the ions corresponding to copper complexes were characterised by low abundances.     

Characterization of electrospray ionization mass spectrometry for N-diisopropyloxyphosphoryl dipeptide methyl esters

A systematic study of the fragmentation pattern of N-diisopropyloxyphosphoryl (DIPP) dipeptide methyl esters in an electrospray ionization (ESI) tandem mass spectrometry (MS/MS) was presented. A combination of accurate mass measurement and tandem mass spectrometry had been used to characterize the major fragment ions observed in the ESI mass spectrum. It was found that the alkali metal ions acted as a fixed charge site and expelled the DIPP group after transferring a proton to the amide nitrogen. For all the N-phosphoryl dipeptide methyl esters, under the activation of a metal ion, the rearrangement product ion at m/z 163 was observed and confirmed to be the sodium adduct of phosphoric acid mono-isopropyl esters (PAIE), via a specific five-membered penta-co-ordinated phosphorus intermediate. However, no rearrangement ion was observed when a beta-amino acid was at the N-terminal. This could be used to develop a novel method for differentiating isomeric compounds when either alpha- or beta-amino acid are at the N-terminus of peptides. From the [M+Na]+ ESI-MS/MS spectra of N-phosphoryl dipeptide methyl esters (DIPP Xaa1 Xaa2 OMe), the peaks corresponding to the [M+Na Xaa1 C3H6]+ were observed and explained. The [M+Na]+ ESI-MS/MS spectra of N-phosphoryl dipeptide methyl esters with Phe located in the C-terminal, such as DIPPValPheOMe, DIPPLeuPheOMe, DIPPIlePheOMe, DIPPAlaPheOMe and DIPPPhePheOMe, had characteristic fragmentation. Two unusual gas-phase intramolecular rearrangement mechanisms were first proposed for this fragmentation. These rearrangements were not observed in dipeptide methyl ester analogs which did not contain the DIPP at the N-terminal, suggesting that this moiety was critical for the rearrangement.     

Determination of three major triterpenoids in epicuticular wax of cabbage (Brassica oleracea L.) by high-performance liquid chromatography with UV and mass spectrometric detection

Lupeol, together with alpha- and beta-amyrins in smaller quantities, has been found for the first time in the epicuticular wax of white cabbage (Brassica oleracea L. convar. capitata (L.) Alef. var. alba DC) leaf surface extract. The three triterpenoids were identified by a new high-performance liquid chromatographic (HPLC) method with UV and mass spectrometric (MS) detection using atmospheric pressure chemical ionization (APCI). All three isomeric compounds gave a parent ion peak at m/z 409 [M+H-18](+) and the relative intensities of some characteristic fragment ion peaks in tandem mass spectrometric (MS-MS) spectra of this parent ion enabled differentiation between the isomers. An additional peak at m/z 439 [M+H](+), which could be oleanonic or ursonic aldehyde, was detected by HPLC-APCI-MS. Saponification of cabbage leaf surface extract with 20% NaOH in methanol at 65 degrees C for 2h had no influence on lupeol, or alpha- or beta-amyrins, but lead to the formation of three additional compounds, which were not identified.     

Enhancement of atmospheric pressure chemical ionization for the determination of free and glycine-conjugated bile acids in human serum

A highly sensitive and accurate method based on the precolumn derivatization of bile acids (BA) with a high ionization efficiency labeling reagent 1,2-benzo-3,4-dihydrocarbazole-9-ethyl-benzenesulfonate (BDEBS) coupled with LC/MS has been developed. After derivatization, BA molecules introduced a weak basic nitrogen atom into the molecular core structure that was readily ionized in commonly used acidic HPLC mobile phases. Derivatives were sufficiently stable to be efficiently analyzed by atmospheric pressure chemical ionization (APCI)-MS/MS in positive-ion mode. The MS/MS spectra of BA derivatives showed an intense protonated molecular ion at m/z [M + H]+. The collision-induced dissociation of the molecular ion produced fragment ions at [MH-H2O]+, [MH-2H2O]+, [MH-3H2O]+. The characteristic fragment ions were at m/z 320.8, 262.8, and 243.7 corresponding to a cleavage of N-CO, O-CO, and C-OCO, respectively, and bonds of derivatized molecules. The selected reaction monitoring, based on the m/z [M+H]+ --> [MH-H2O]+, [MH-2H2O]+, [MH-3H2O]+, 320.8, 262.8, and 243.7 transitions, was highly specific for the BA derivatives. The LODs for APCI in a positive-ion mode, at an S/N of 5, were 44.36-153.6 fmol. The validation results showed high accuracy in the range of 93-107% and the mean interday precision for all standards was <15% at broad linear dynamic ranges (0.0244-25 nmol/mL). Good linear responses were observed with coefficients of > 0.9935 in APCI/MS detection. Therefore, the facile BDEBS derivatization coupled with mass spectrometric analysis allowed the development of a highly sensitive and specific method for the quantitation of trace levels of the free and glycine-conjugated BA from human serum samples.     

Evaluation of eluents in thermospray liquid chromatography-mass spectrometry for identification and determination of pesticides in environmental samples.

The influence of different eluents in positive and negative ion mode thermospray liquid chromatography-mass spectrometry was studied with several groups of pesticides, including carbamates, chlorotriazines, phenylureas, phenoxy acids and organophosphorus and quaternary ammonium compounds, and the corresponding degradation products. Using the positive ion mode in combination with reversed-phase eluents the base peaks generally corresponded either to [M + H]+ for the chlorotriazines and their hydroxy metabolites or to [M + NH4]+ for the carbamates, the phenylureas, the organophosphorus pesticides and their oxygen analogues. In the negative ion mode different processes such as (dissociative) electron-capture and anion attachment mechanisms occurred. Fragment ions such as [M - CONHCH3]- for the carbamates, [M - H]- for the chlorotriazines, phenylureas and chlorinated phenoxy acids and [M].-, [M - R]- (R being a methyl or ethyl group) for organophosphorus pesticides were usually formed. Depending on the eluent additive used (ammonium acetate, ammonium formate and/or chloroacetonitrile), three different adduct ions were formed: [M + CH3COO]-, [M + HCOO]- and [M + Cl]-. Normal-phase eluents with cyclohexane, n-hexane and/or dichloromethane provided more structural information and enhanced the response of several compounds. The positive ion mode was useful for the detection of chlorinated phenoxy acids and chlorophenols which could not be detected in the positive ion mode using reversed-phase systems. The base peaks generally corresponded to [M].+, [M + H]+ or [M - Cl]+. For the characterization of difenzoquat, a quaternary ammonium pesticide of which trace level analysis is troublesome, a post-column ion-pair extraction system was used. An aqueous mobile phase with a sulphonate-type counter ion was applied and an extraction solvent containing cyclohexane-dichloromethane-n-butanol (45:45:10) was used in thermospray liquid chromatography-mass spectrometry. Illustrative examples of the determination of residue levels of pesticides in soil matrices are shown.     

Determination of fatty alcohol ethoxylates by derivatization with phthalic anhydride followed by liquid chromatography with UV-vis detection

The esterification of fatty alcohol ethoxylates (FAEs) with phthalic anhydride in 1,4-dioxane was studied. At 110 degrees C and in the presence of urea, which increased the reaction rate, esterification was completed in 60 min. The reaction yield did not decrease when the sample contained up to 50% water. For the non-ethoxylated alcohols, the UV-vis response factors of the derivatives were not significantly different from each other (f=1 for C12E0 as reference). The response factors decreased when the number of ethylene oxide units, m, increased, reaching constant values of ca. 0.40 and 0.65 for the n=8 and 18 series, respectively, when m>or=3. Using a C8 column and gradient elution with acetonitrile/water plus 0.1% acetic acid, FAEs in industrial mixtures and cleaning products were characterized. At column temperatures of 25 and 35 degrees C, homologous series with even values of n from 8 up to 20, were resolved up to m=14 and 18, respectively, and at 25 degrees C, series with consecutive even and odd values of n were resolved up to m=7. Within the series, superior resolution of the ethoxymers with large values of m was achieved; however, the elution order was reversed for the m=1 and 0 ethoxymers, which produced overlapping of a few peaks within the series. A simple procedure for the accurate prediction of the concentrations of all the ethoxymers in industrial samples was described. After preconcentration with C18 solid-phase extraction cartridges, FAEs were also characterized and quantified in environmental samples (river and sea water). The LODs were ca. 2 microM (S/N=3) in the injected solutions.     

Influence of solvent and counter ion on complexes of 2,5-bis(2-pyridyl)-1,3,4-oxadiazole with iron (II) and (III) studied by electrospray ionization mass spectrometry

The effect of solvent and counter ion on the complexes of 2,5-bis(2-pyridyl)-1,3,4-oxadiazole (1) with Fe+2 and Fe+3 has been studied by electrospray ionization mass spectrometry (ESI/MS). As expected, upon ESI conditions the metal reduction proceeds, but it can be deduced that complexes with Fe+2 are favored over those with Fe+3. When methanol is used as solvent, the formation of complexes of stoichiometry 2:1 and 1:1 with counter ion attached (monovalent anion) is favored, for example, [1(2)+FeCl]+ ion. The use of methanol/water (1/1) as solvent favors the formation of complexes of stoichiometry 2:1 and 3:1, namely doubly charged [1(2)+Fe]+2 and [1(3)+Fe]+2 ions. The complexes containing anion of oxidative properties (ClO4-, NO3-), when the higher cone voltage is applied, yield unusual species [1n+FeOm]+ (n=1, 2; m=1, 2). The use of divalent counter ion (SO4(-2)) resulted in formation of complexes containing two iron cations, namely [1n+Fe2SO4]+2 (n=2, 3, 4) ions. These ions can be regarded as Fe-1 complexes bridged by a sulfate anion.     

Structural determination of cyclitol derivatives by fast-atom bombardment tandem mass spectrometry

Three cyclitol derivatives were isolated from the marine sponge Sarcotragus sp. by reversed-phase high-performance liquid chromatography and analyzed by fast-atom bombardment mass spectrometry (FAB-MS). Their structural elucidation was carried out with FAB tandem mass spectrometry (FAB-MS/MS). FAB-MS spectra produced a significant abundance of the sodium adducts [M+Na]+ and [M+2Na-H]+ from a mixture of m-NBA and NaI. In addition, trifluoroacetylation of the cyclitol derivatives was used for confirmation of the presence of the cyclitol ring. High abundance [M-5H+5CF3CO+Na]+ ions were observed in the FAB-MS spectra of the trifluoroacetyl-cyclitol derivatives. Collision-induced dissociation (CID) of the [M+Na]+ ions produced diverse product ions via a series of dissociative processes. Charge-remote fragmentation (CRF) patterns of [M+Na]+ ions were very useful for the identification of product ions which are characteristic for the cyclitol ring and long hydrocarbon chains substituted at the glycerol backbone. Moreover, the CID-MS/MS spectra of the [M+Na]+ ions yielded characteristic product ions at m/z 53, 83, 113, 155 and 171 for the cyclitol moiety, and at m/z 213, 229 and 245 for the glycerol backbone attached to the cyclitol ring.     

Mass spectrometric and tandem mass spectrometric behavior of nitrocatechol glucuronides: A comparison of atmospheric pressure chemical ionization and electrospray ionization

The mass spectrometric (MS) and tandem mass spectrometric (MS/MS) behavior of six nitrocatechol-type glucuronides using atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) was systematically studied, and the effect of operation parameters on the fragmentations are presented. The positive ion APCI- and ESI-MS spectra showed an intense protonated molecule and the respective negative ion spectra a deprotonated molecule with minimal fragmentation. The main fragment ions in the MS/MS spectra of the protonated and deprotonated molecules were [M + H - Glu]+ and [M - H - Glu]-, respectively, formed by the loss of the glucuronide moiety. The measured limits of detection indicated that ESI is a significantly more efficient ionization method than APCI in the negative and positive ion modes for the compounds studied. MS/MS was found to be less sensitive, but more reliable and simple than MS due to the absence of chemical noise.