Mobility labeling for parallel CID of ion mixtures

An ion mobility/mass spectrometry technique has been developed to record collision-induced dissociation patterns for multiple ions in a parallel fashion. In this approach, a mixture of ions is separated in a drift tube on the basis of differences in mobilities through a buffer gas. As the ions exit the drift tube, they are accelerated into a collision cell and the ensuing fragment ions are dispersed by differences in mass-to-charge (m/z) ratios in a time-of-flight mass spectrometer. Fragment ions that are formed in the collision cell have drift times that are coincident with their antecedent parent ions, allowing the origin of all fragments formed from the mixture of ions to be determined. The approach is demonstrated by examining fragmentation patterns of the [M + H]+ parent and a series of a-, b-, and y-type fragments of [D-Ala2,3]methionine enkephalin.     

Atmospheric pressure covalent adduct chemical ionization tandem mass spectrometry for double bond localization in monoene- and diene-containing triacylglycerols

We report a method to elucidate the structure of triacyl-glycerols (TAGs) containing monoene or diene fatty acyl groups by atmospheric pressure covalent adduct chemical ionization (APCACI) tandem mass spectrometry using acetonitrile as an adduct formation reagent. TAGs were synthesized with the structures ABB and BAB, where A is palmitate (C16:0) and B is an isomeric C18 monoene unsaturated at position 9, 11, or 13 or an isomeric diene unsaturated at positions 9 and 11, 10 and 12, or 9 and 12. In addition to the species at m/z 54 observed in previous CI studies of fatty acid methyl esters, we also found that ions at m/z 42, 81, and 95 undergo covalent reaction with TAGs containing double bonds to yield ions at m/z 40, 54, 81, and 95 units greater than that of the parent TAG: [M + 40]+, [M + 54]+, [M + 81]+, and [M + 95]+ ions. When collisionally dissociated, these ions fragment to produce two or three diagnostic ions that locate the double bonds in the TAG. In addition, ions [RCH=C=O + 40]+ and [RCH=C=O + 54]+ formed from collisional dissociation are of strong abundance in MS/MS spectra, and collisional activation of these ions produces two intense confirmatory diagnostic ions in the MS3 spectra. Fragment ions reflecting neutral loss of an sn-1-acyl group from [M + 40]+ and [M + 54]+ are more abundant than those reflecting neutral loss of an sn-2-acyl group, analogous to previous reports for protonated TAGs. The position of each acyl group on the glycerol backbone is thus determined by the relative abundances of these ions. Under the conditions in our instrument, the [M + 40]+ adduct is at the highest signal and also yields all information about the double bond position and TAG stereochemistry. With the exception of geometries about the double bonds, racemic TAG isomers containing two monoenes or dienes and a saturate can be fully characterized by APCACI-MS/MS/MS.     

Parent and neutral loss monitoring on a quadrupole ion trap mass spectrometer: screening of acylcarnitines in complex mixtures

A novel and practical technique for performing both parent and neutral loss (P&NL) monitoring experiments on a quadrupole ion trap mass spectrometer is presented. This technique is capable of performing scans analogous to the parent and neutral loss scans routinely applied on tandem-in-space instruments and allows for the screening of a sample to detect analytes of a specific compound class on a chromatographic time-scale. Acylcarnitines were chosen as the model compound class to demonstrate the analytical utility of P&NL monitoring because of their amenability to electrospray ionization (ESI), their unique and informative MS/MS fragmentation pattern, and their importance in biological functions. The [M + H]+ ions of all acylcarnitines dissociate to produce neutral losses of 59 and 161 amu and common product ions at m/z 60, 85, and 144. Both the neutral loss monitoring of 59 amu and the parent ion monitoring of m/z 85 are shown to be capable of identifying acylcarnitine [M + H]+ ions in a synthetic mixture and spiked pig plasma. The neutral loss monitoring of 59 amu is successful in detecting acylcarnitines in an unspiked pig plasma sample.     

Analysis of intact tissue by intermediate-pressure MALDI on a linear ion trap mass spectrometer

The use of an intermediate-pressure matrix-assisted laser desorption/ionization (IP-MALDI) source working at 0.17 Torr on a linear ion trap (LIT) was investigated for the analysis of tissue specimens, in particular, spinal cord sections. MALDI, with 2,5-dihydroxybenzoic acid (DHB) as the matrix, was employed for the detection of phospholipids. The matrix was applied to the tissue using electrospray to avoid analyte migration. The results indicate that analyzing tissue specimens at nontraditional MALDI vacuum pressures is possible. Coupling MALDI to an LIT permits the use of MSn, which is critical for the ability to identify compounds desorbed directly from tissue specimens. Using MSn, ions detected from m/z 600-1000 were characterized as phosphatidlycholines, PC. Specifically, using tandem MS, PC ions could be classified as either [M + H]+ or [M + Na]+ because the fragmentation patterns of protonated and sodiated phosphatidlycholines follow different pathways.     

Effects of mobile-phase additives, solution pH, ionization constant, and analyte concentration on the sensitivities and electrospray ionization mass spectra of nucleoside antiviral agents

The effects of various mobile-phase additives, solution pH, pKa, and analyte concentration on electrospray ionization mass spectra of a series of purine and pyrimidine nucleoside antiviral agents were studied in both positive and negative ion models. The use of 1% acetic acid resulted in good HPLC separation and the greatest sensitivity for [M + H]+ ions. In the negative ion mode, 50 mM ammonium hydroxide gave the greatest sensitivity for [M - H]- ions. The sensitivities as [M + H]+ ions were significantly larger than the sensitivities as [M - H]- ions for purine antiviral agents. Vidarabine monophosphate and pyrimidine antiviral agents, however, showed comparable or greater sensitivities as [M - H]- ions. The sensitivity as [M + H]+ showed no systematic variation with pH; however, the sensitivity as [M - H]- did increase with increasing pH. At constant pH, the ion intensity of the protonated species increased with increasing pKa. At higher analyte concentrations, dimer (M2H+) and trimer (M3H+) ions were observed. [M + Na]+ adducts were the dominant ions with 0.5 mM sodium salts for these compounds. The spectra of the more basic purine antiviral agents showed no [M + NH4]+ adduct ions, but [M + NH4]+ ions were the major peaks in the spectra of the less basic pyrimidine antiviral agents with ammonium salts. The ammonium adduct ion was formed preferentially when the proton affinity of the analyte was close to that of NH3. Abundant [M + OAc]- ions were observed for all of the antiviral agents except vidarabine monophosphate from solutions with added HOAc, NaOAc, and NH4OAc. The utility of mobile phases containing 1% HOAc or 50 mM NH4OH was demonstrated for chromatographic separations.     

Sequencing of argentinated peptides by means of electrospray tandem mass spectrometry.

A strategy for semiautomatic sequencing of argentinated (silver-containing) oligopeptides has been developed. Sequencing is based on a search algorithm that identifies a triplet peak relationship in a product ion spectrum of the [M + Ag]+ ion of an oligopeptide. The ions that constitute a triplet are [bn + OH + Ag]+, [bn - H + Ag]+, and [a(n) - H + Ag]+, which are separated by 18 and 28 m/z units, respectively. The difference in the m/z values of adjacent triplets identifies the residue that is "cleaved". Observation of the [yn + H + Ag]+ ion containing the cleaved residue confirms the assignment. Sequencing of argentinated tryptic peptides may prove useful for automated proteome analysis via the sequence tag method.     

Charge-state-dependent sequence analysis of protonated ubiquitin ions via ion trap tandem mass spectrometry

One of the major factors governing the "top-down" sequence analysis of intact multiply protonated proteins by tandem mass spectrometry is the effect of the precursor ion charge state on the formation of product ions. To more fully understand this effect, electrospray ionization coupled to a quadrupole ion trap mass spectrometer, collision-induced dissociation, and gas-phase ion/ion reactions have been employed to examine the fragmentation of the [M + 12H]12+ to [M + H]+ ions of bovine ubiquitin. At low charge states (+1 to +6), loss of NH3 or H2O from the protonated precursor and directed cleavage at aspartic acid residues was observed. At intermediate charge states, (+7, +8, and +9), extensive nonspecific fragmentation of the protein backbone was observed, with 50% sequence coverage obtained from the [M + 8H]8+ ion alone. At high charge states, (+10, +11, +12), the single dominant channel that was observed was the preferential fragmentation of a single proline residue. These data can be readily explained in terms of the current model for intramolecular proton mobilization, that is, the "mobile proton model", the mechanisms for amide bond dissociation developed for protonated peptides, as well as the structures of the multiply charged ions of ubiquitin in the gas phase, examined by ion mobility and hydrogen/deuterium exchange measurements.     

Dissociation of multiple protein ion charge states following a single gas-phase purification and concentration procedure

The formation of a range of precursor ion charge states from a single concentrated and purified charge state, followed by activation of each charge state, is introduced as a means to obtain more protein structural information than is available from dissociation of a single charge state alone. This approach is illustrated using off-resonance collisional activation of the [M + 8H]8+ to [M + 6H]6+ precursor ions of the bacteriophage MS2 viral coat protein following concentration and purification of the [M + 8H]8+ charge state. This range of charge states was selected on the basis of an ion trap collisional activation study of the effects of precursor ion charge state on the dissociation of the [M + 12H]12+ to [M + 5H]5+ ions. Gas-phase ion/ion proton-transfer reactions and the ion parking technique were applied to purify and concentrate selected precursor ion charge states as well as to simplify the product ion spectra. The high-charge-state ions fragment preferentially at the N-terminal side of proline residues while the product ion spectra of the lowest charge states investigated are dominated by C-terminal aspartic acid cleavages. Maximum structural information is obtained by fragmentation of the intermediate-charge states.     

Mass spectrometry and tandem mass spectrometry of citrus limonoids

Methods for atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS/MS) of citrus limonoid aglycones and electrospray ionization tandem mass spectrometry (ESI-MS/MS) of limonoid glucosides are reported. The fragmentation patterns of four citrus limonoid aglycones (limonin, nomilin, obacunone, and deacetylnomilin) and six limonoid glucosides, that is, limonin 17-beta-D-glucopyranoside (LG), nomilin 17-beta-D-glucopyranoside (NG), nomilinic acid 17-beta-D-glucopyranoside (NAG), deacetyl nomilinic acid 17-beta-D-glucopyranoside (DNAG), obacunone 17-beta-D-glucopyranoside (OG), and obacunoic acid 17-beta-D-glucopyranoside (OAG) were investigated using a quadruple mass spectrometer in low-energy collisionally activated dissociation (CAD). The four limonoid aglycones and four limonoid glucosides (LG, OG, NAG, and DNAG) were purified from citrus seeds; the other two limonoid glucosides (NG and OAG) were tentatively identified in the crude extract of grapefruit seeds by ESI mass spectrometry in both positive and negative ion analysis. Ammonium hydroxide or acetic acid was added to the mobile phase to facilitate ionization. During positive ion APCI analysis of limonoid aglycones, protonated molecular ion, [M + H]+, or adduct ion, [M + NH3 + H]-, was formed as base peaks when ammonium hydroxide was added to the mobile phase. Molecular anions or adduct ions with acetic acid ([M + HOAc - H] and [M + HOAc]-) or a deprotonated molecular ion were produced during negative ion APCI analysis of limonoid aglycones, depending on the mobile-phase modifier used. Positive ion ESI-MS of limonoid glucosides produced adduct ions of [M + H + NH3]+, [M + Na]+, and [M + K]+ when ammonium hydroxide was added to the mobile phase. After collisionally activated dissociation (CAD) of the limonoid aglycone molecular ions in negative ion APCI analysis, fragment ions indicated structural information of the precursor ions, showing the presence of methyl, carboxyl, and oxygenated ring structure. CAD of the adduct ion [M + H + NH3]+ of limonoid glucosides produced the aglycone moiety corresponding to each glucoside. The combination of mass spectrometry and tandem mass spectrometry provides a powerful technique for identification and characterization of citrus limonoids.     

Analysis of epipolythiodioxopiperazines in fungus Chaetomium cochliodes using HPLC-ESI-MS/MS/MS

A series of epipolythiodioxopiperazines in the fungus Chaetomium cochliodes was investigated using reversed-phase liquid chromatography with diode array detection and electrospray quadrupole time-of-flight-type tandem mass spectrometry in the positive ion mode. The fragmentation of protonated molecular ions including low-abundance parent ions, [M+H]+ for five known epipolythiodioxopiperazines, dethiotetra(methylthio)chetomin, chaetocochins A-C, and chetomin, was carried out using low-energy collision-induced electrospray ionization tandem spectrometry. It was found that McLafferty rearrangements occurred in the CID processes and produced a complementary pair of characteristic fragment ions containing piperazine rings (fused and unfused), especially to determine the number of S atoms on each ring. The fragmentation differential between [M+H]+ and [M+Na]+ was uncovered. Complementary fragmentation information obtained from [M+H]+ and [M+Na]+ precursor ions is especially valuable for rapid identification of epipolythiodioxopiperazines. A likely known compound, possibly related to chetoseminudin A, and three new species of epipolythiodioxopiperazines from the fungus C. cochliodes were identified or tentatively characterized based on tandem mass spectra of known ones.     

A validated liquid chromatography/tandem mass spectrometry assay for cis-amminedichloro(2-methylpyridine)platinum(II) in human plasma ultrafiltrate

The clinical use of platinum drugs as anticancer agents has encountered problems when relating pharmacokinetic profiles with efficacy and toxicity is attempted. This has been mainly due to the lack of specific and sensitive analytical methodology to examine concentrations of the unbound drug in plasma. The presence of a carbocyclic ring on the new drug, cis-amminedichloro(2-methylpyridine)platinum(II) (ZD0473) suggested that it would be possible to develop the first stable isotope dilution LC/MS assay for a platinum drug in human plasma ultrafiltrate samples. The dichloro form of the drug exists in equilibrium with at least two aquated forms in plasma. The molecular form of the drug, therefore, depends on the length of time that the plasma sample is maintained at room temperature before freezing. Therefore, we have developed a method that quantitatively converts the aquated species back to the dichloro form of the parent drug so that a single molecular species can be analyzed. Selected reaction monitoring was performed on the transition of m/z 393 [M + NH4]+ to m/z 304 [M + NH4 -NH3 - 2 x HCl]- for ZD0473, and m/z 400 [M + NH4]+ to m/z 310 [M + NH4 - NH3 - HCl - 2HCl]+ for [2H7]ZD0473. The standard curves were fitted to a quadratic regression over the range from 10 to 5000 ng/mL in human plasma ultrafiltrate. The lower limit of quantitation for ZD0473 was 10 ng/mL for 100 microL of plasma ultrafiltrate. This simple, rapid, reliable, and sensitive method of quantitation had excellent accuracy and precision. The method provided adequate sensitivity for the analysis of plasma ultrafiltrate samples from a phase II study in which ZD0473 was administered to patients as an intravenous infusion at a dose of 150 mg/m2.     

Scrubbing ions with molecules: kinetic studies of chemical noise reduction in mass spectrometry using ion-molecule reactions with dimethyl disulfide

The kinetics and product distributions of the reactions of dimethyl disulfide (DMDS) have been investigated with a group of chemical background ions commonly observed in atmospheric pressure ionization (API) mass spectrometry (MS) in order to assess the value of this molecule in filtering (or "scrubbing") these ions by changing their mass/charge (m/z) ratio. The measurements were taken with a novel electrospray ionization/selected ion flow tube/QqQ tandem mass spectrometer. The background ions studied include those with m/z 42 (protonated acetonitrile, ACN), 83 (protonated ACN dimer), 99 (protonated phosphoric acid), 117 (water cluster of m/z 99), 131 (methanol cluster of m/z 99), 149 (protonated phthalic anhydride, formed from the phthalates), and 327 (protonated triphenyl phosphate). In addition, reactions of DMDS have been studied with two model analytes--protonated caffeine and doubly protonated bradykinin--in order to assess the selectivity of DMDS reactivity. All the measurements were taken at 295 +/- 2 K in helium buffer gas at a pressure of 0.35 +/- 0.01 Torr. DMDS was observed to react efficiently with m/z 42 (ACNH+), 149 (from phthalates), and 99 (protonated phosphoric acid), with k/kc=0.91, 0.47, and 0.38, respectively. Only proton transfer was observed with ACNH+, followed by the secondary reaction of [DMDSH]+ with DMDS to yield [CH3S-S(CH3)-SCH3]+. Ligation of DMDS was the dominant primary channel observed for the reaction of the m/z 149 background ion; however, some proton transfer also was observed. Both of these primary product ions react further with DMDS to yield [CH3S-S(CH3)-SCH3]+, the structure of which we have determined computationally using DFT calculations. Only the sequential ligation with two DMDS molecules was observed for the reaction of the m/z 99 ion. Reactions of DMDS with m/z 117 [H3PO4 + H + H2O]+ and m/z 131 [H3PO4 + H + MeOH]+ were observed to proceed with k/kc=0.71 and 0.058, respectively. Ligand substitution of DMDS for H2O predominated ( approximately 94%) over DMDS ligation ( approximately 6%) in the reaction with m/z 117, while only DMDS ligation was observed for the reaction of m/z 131 with DMDS. In contrast, the reactions of DMDS with ions of m/z 83 (protonated dimer of ACN) and 327 (protonated triphenyl phosphate) were extremely inefficient, with k/kc=0.0042 and 0.0079, respectively. The higher reactivity of DMDS toward ACNH+ (m/z 42) compared to (ACN)2H+ (m/z 83) is attributed to the lower proton affinity of the unsolvated ACN. The reactivity of DMDS toward the two model analyte ions studied-protonated caffeine and doubly protonated bradykinin-was negligible, with k/kc=0.0073 and 0.010, for the respective reactions. These results suggest that, under appropriate reagent pressure conditions, DMDS can be an appropriate reagent for chemically filtering out many common API-MS background ions, without significantly affecting the observed intensity of analyte peaks.     

"Internal residue loss": rearrangements occurring during the fragmentation of carbohydrates derivatized at the reducing terminus

Rearrangement reactions involving migration of fucose and, occasionally, other residues have been found in the CID spectra of [M + H]+ and [M + 2H]2+ ions, but not [M + Na]+ ions, generated from several O-linked carbohydrates and milk sugars derivatized at their reducing termini with aromatic amines such as 2-aminobenzamide. Such rearrangements, which are similar to those reported by other investigators from several underivatized carbohydrates and glycosides, cause an apparent loss of sugar residues from within a carbohydrate chain and can produce ambiguous results during spectral interpretation. A mechanism, involving initial protonation of the amine nitrogen atom of the derivative, is proposed to account for the formation of the observed ions.     

Identification of selenium-containing glutathione S-conjugates in a yeast extract by two-dimensional liquid chromatography with inductively coupled plasma MS and nanoelectrospray MS/MS detection

An approach for the identification of unknown selenium-containing biomolecules was developed, enabling the identification of selenodiglutathione (GS-Se-SG) and the mixed selenotrisulfide of glutathione and cysteinylglycine (GS-Se-SCG) in aqueous yeast extracts. The method consists of two-dimensional liquid chromatography, inductively coupled plasma mass spectrometry (ICPMS) and nanoelectrospray tandem mass spectrometry. Analytes were separated by size-exclusion chromatography followed by preconcentration and separation on a porous graphitic carbon HPLC column. The HPLC effluent was monitored for selenium by ICPMS, and two selenium-containing fractions were isolated and analyzed by nanoelectrospray MS. The nanoelectrospray technique has a low sample consumption of approximately 80 nL/min, enabling a preconcentration of the sample to a few microliters. Mass spectra of the two fractions showed the characteristic Se isotopic pattern centered at m/z 693.1 and 564.0 for the [M + H]+ 80Se ions. MS/MS spectra of adjacent parent ions confirmed the presence of Se. The two selenium species were identified as GS-Se-SG and GS-Se-SCG by collision induced dissociation (CID). The accurately measured masses of the most abundant 691 and 693 u parent ions are in good agreement (differences = 3 ppm) with the theoretical masses. To our knowledge, this is the first identification of GS-Se-SG and GS-Se-SCG in biological matrixes by MS/MS.     

Identification and characterization of conjugated fatty acid methyl esters of mixed double bond geometry by acetonitrile chemical ionization tandem mass spectrometry

Fatty acids with conjugated double bonds have attracted great interest because of their reported potent bioactivities. However, there are currently no rapid methods for their structural characterization. We report here a convenient mass spectrometry-based strategy to establish double bond geometry by analysis of collisional dissociation products of cis/trans and trans/cis conjugated linoleic acids (CLAs), as methyl esters, and to distinguish CLAs from homoallylic (methylene-interrupted) fatty acids in a single-stage mass spectrum. A series of CLA standards with double bond positions 6,8; 7,9; 8,10; 9,11; 10,12; 11,13; 12,14; and 13,15, with all four possible geometries (cis/trans; trans/cis; cis/cis; trans/trans) were analyzed. The m/z 54 (1-methyleneimino)-1-ethenylium ion, generated by self-reaction of acetonitrile under chemical ionization conditions, reacts with unsaturated fatty acids to yield an [M + 54]+ ion, which decomposes in the single-stage mass spectrum by loss of neutral methanol to form [M + 54 - 32]+. The ratio of [M + 54]+/[M + 54 - 32]+ in the single-stage mass spectra of CLA isomers is 1 order of magnitude less than for homoallylic diene FAME. Collisional dissociation of the [M + 54]+ ion yields two diagnostic ions that contain the alpha- and omega-carbon atoms and is characteristic of double bond position in the analyte. The fragment vinylic to the trans double bond is significantly more abundant than that for the cis double bond, revealing double bond geometry. The ratio of alpha to we diagnostic ion abundances is >4.8 for cis/trans isomers, <0.5 for trans/cis isomers, and 0.7-3.2 for cis/cis and trans/trans isomers. This method provides a rapid alternative to conventional conjugated fatty acid analysis and, together with complementary elution time information provided by gas chromatography, enables rapid, positive identification of double bond position and geometry in most CLA FAME.     

Determination of ginsenosides in plant extracts from Panax ginseng and Panax quinquefolius L. by LC/MS/MS

An HPLC/MS/MS method has been developed for the characterization and quantification of ginsenosides contained in extracts of the root of Panax ginseng (Korean ginsengs) and Panax quinquefolius L. (American ginsengs). The [M + H]+ and [M + Na]+ ions were observed for ginsenoside standards (Rb1, Rb2, Rc, Rd, Re, Rf, Rg1) and four different ginseng extracts. The glycosidic linkages, the core, and the attached sugar(s) of the ginsenosides can be determined from the collision-induced dissociation spectra from the protonated molecules. The relative distribution of these ginsenosides in each extract of American or Korean ginseng was established.     

Calibration of ion effective temperatures achieved by resonant activation in a quadrupole ion trap

The present paper describes a calibration of the ion effective temperatures as a function of the resonant activation amplitude in a quadrupole ion trap mass spectrometer. MS/MS experiments are performed on leucine enkephalin (M + H)+, bradykinin (M + H)+, (M + 2H)2+, and (M + 3H)3+, and ubiquitin (M + 11H)11+. For each amplitude, the effective temperature is calculated as the temperature that would give the same dissociation rate constant as the one observed and is calculated using published Arrhenius parameters. The effective temperature is found to be linearly dependent on the activation amplitude on the range investigated. The dependence of the slope and of the intercept of the T(eff) = f (amplitude) functions on the parent ion m/z is examined and an equation is derived to calibrate the ion effective temperature between 365 and 600 K. Below 365 K, a deviation from linearity is expected. Above 600 K, the validity of the equation will depend on whether the rapid energy exchange limit is still reached. Calculating backward, the Arrhenius parameters from the measured dissociation rates using this calibration show excellent agreement with the published values. The calibration can therefore be used to determine Arrhenius activation parameters from dissociation kinetics under resonant activation in quadrupole ion trap mass spectrometers.     

Acetonitrile covalent adduct chemical ionization mass spectrometry for double bond localization in non-methylene-interrupted polyene fatty acid methyl esters

Covalent adduct chemical ionization (CACI) using a product of acetonitrile self-reaction, (1-methyleneimino)-1-ethenylium (MIE; CH2=C=N+=CH2), has been investigated as a method for localizing double bonds in a series of 16 non-methylene-interrupted fatty acid methyl esters (NMI-FAME) of polyenes with three and more double bonds. As with polyunsaturated homoallylic (methylene-interrupted) FAME and conjugated dienes, MIE (m/z 54) reacts across double bonds to yield molecular ions 54 mass units above the parent analyte. [M + 54]+ ions of several 20- and 22-carbon FAME that include one double bond in the C2-C3 position separated by two to five methylene units from a three, four, or five C homoallylic system dissociated according to rules for the homoallylic system, with an additional fragment corresponding to cleavage between the lone double bond and the carboxyl group and defining the position of the lone double bond. Triene FAME with both methylene and ethylene interruption yielded characteristic fragments distinguishable from homoallylic trienes. Fragmentation of fully conjugated trienes in the MS-1 spectra yields ratios of [M + 54]+/[M + 54 - 32]+ (loss of methanol) near unity, which distinguishes them from homoallylic FAME having a ratio of 8 or more; collisionally activated dissociation of [M + 54]+ yields a series of ions, including some rearrangement products, indicative of double bond position. Unlike conjugated dienes, fully conjugated triene diagnostic ion signal ratios did not follow any pattern based on double bond geometry. Partially conjugated trienes behave similarly to monoenes and conjugated dienes, yielding [M + 54]+/[M + 54 - 32]+ of 2-3 and, permitting them to be assigned as partially conjugated FAME using the MS-1 spectrum. They yield unique MS/MS spectra with weaker but assignable fragment ions, along with a diagnostic fragment that locates the lone double bond and permits 6,10,12-octatrienoate to be distinguished from 6,8,12-octatrienoate. The presence of a triple bond did not affect fragment formation in a methylene-interrupted yne-ene but did change fragments in a conjugated yne-ene. These data extend the principle of double bond localization by acetonitrile CACI-MS/MS to double bond structure in complex FAME found in nature.     

Cyanobacteria and their toxins in Guanting Reservoir of Beijing, China

The present study investigated the cyanobacteria and one family of their toxins-microcystins (MCs) in Guanting Reservoir of Beijing, China. The dominant species in the cyanobacteria found in August and September of 2006 was Microcystis, which accounted 99% of total algal cells. The specific species of the Microcystis in the cyanobacteria included Microcystis ichthyobalbe, Microcystis novacekii, Microcystis botrys and Microcystis aeruginosa which had different ratios in different sites. The qualitative analysis by HPLC showed that two microcystins were contained in cyanobacteria and one microcystin was in water of the reservoir. The major microcystins were microcystin-RR (MC-RR) and microcystin-LR (MC-LR), but only MC-LR was detected in water. The quantitative analysis by HPLC indicated that the maximum concentrations of MC-RR and MC-LR contained in cyanobacteria were 0.74 and 0.41 mg/g dry weight, respectively. The maximum microcystin concentration in water was 1.15 microg/L and others were below 1 microg/L.     

Direct determination of dibutyl and monobutyl phosphate in a tributyl phosphate/nitric aqueous-phase system by electrospray mass spectrometry

Electrospray ionization mass spectrometry was tested for its potential use in the quantification of monobutyl phosphate (H2MBP) and dibutyl phosphate (HDBP), two degradation products of tributyl phosphate (TBP), the extractant used in the nuclear fuel reprocessing known as the PUREX process. Detection and quantification of these phosphate esters by electrospray in positive and negative ionization mode are reported in this study. This fast and reliable method, which does not require any preliminary sample extraction, appears to be very attractive for process control. Negative ionization mode gave abundant [M - H]- ions for both HDBP and H2MBP products. Thus, the concentration of H2MBP between 0.1 and 10 g/L in concentrated aqueous nitrate solutions can be precisely determined. Moreover, the concentration of HDBP up to 1 g/L in a TBP matrix was evaluated in this mode. For HDBP concentrations below 1 g/L, detection in the positive ionization mode appeared to be attractive. TBP and HDBP cluster detection allowed quantitative HDBP determination. Indeed, small amounts of HDBP in commercial TBP (60 mg/L) could be directly quantified using the specific [2TBP, HDBP + H]+ cluster at m/z 743.