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991.
Hsu FF Turk J Shi Y Groisman EA 《Journal of the American Society for Mass Spectrometry》2004,15(1):1-11
Acylphosphatidylglycerol (Acyl-PG), a polar lipid class containing three fatty acyl groups, was isolated from Salmonella bacteria and characterized by tandem quadrupole and quadrupole ion-trap mass spectrometric methods with electrospray ionization. The structural characterization of the acyl-PG with various acyl groups (A-B/C-PG, where A not equal B not equal C) is based on the findings that the carboxylate anions (R(x)CO(2)(-)) arising from sn-2 (R(2)CO(2)(-)) is more abundant than that arising from sn-3' (R(3')CO(2)(-)), which is much more abundant than that arising from sn-1 (R(1)CO(2)(-)). This information provides a simple method for determination of the fatty acyl moieties and their positions in the molecule. The structural identification of the molecule can also be achieved by the findings that the fragment ion reflecting the ketene loss at sn-2 is more prominent than that reflecting the acid loss (i.e., [M - H - R'(2)CH=CO](-) > [M - H - R(2)CO(2)H](-)), while the ion arising from acid loss at sn-1 or sn-3' is, respectively, more abundant than the corresponding ketene loss (i.e., [M - H - R(1)CO(2)H](-) > [M - H - R'(1)CH=CO](-); [M - H - R(3')CO(2)H](-) > [M - H -R'(3')CH=CO](-)). The identity of the acyl moiety at sn-3' can be confirmed by an acyl-glycerophosphate anion observed in the product-ion spectrum obtained with a triple-stage quadrupole (TSQ) instrument, but not in that obtained with an ion-trap mass spectrometer (ITMS). However, the MS(2)-spectrum obtained with an ITMS is featured by the ion series that abundances of [M - H - R'(2)CH=CO - R(3)CO(2)H - 74](-) > [M - H - R'(2)CH=CO - R(1)CO(2)H - 74](-) z.Gt; [M - H - R'(1(or 3'))CH=CO - R(3'(or 1))CO(2)H - 74](-). This information also facilitates structural elucidation of the acyl-PG subclass that contains various acyl substituents. Structural identifications of molecular species having two identical fatty acyl substituents at sn-1, sn-2, or sn-3' or consisting of more than one isomeric structures are also demonstrated. The identities of the minor isomeric species in the molecules can be revealed by the aforementioned structural information arising from the various ion series combined. 相似文献
992.
Karlsson NG Schulz BL Packer NH 《Journal of the American Society for Mass Spectrometry》2004,15(5):659-672
Neutral O-linked oligosaccharides released from the salivary mucin MUC5B were separated and detected by negative ion LC-MS and LC-MS(2). The resolution of the chromatography and the information obtained from collision induced dissociation of detected [M - H](-) ions were usually sufficient to identify the sequence of individual oligosaccharides, illustrated by the fact that 50 different oligosaccharides ranging from disaccharides to nonasaccharides could be assigned from the sample. Fragmentation was shown to yield mostly reducing end sequence fragments (Z(i) and Y(i)), enabling primary sequence assignment. Specific fragmentation pathways or patterns were also detected giving specific linkage information. The reducing end core (Gal/GlcNAcbeta1-3GalNAcol or Gal/GlcNAcbeta1-3(GlcNAcbeta1-6)GalNAcol) could be deduced from the pronounced glycosidic C-3 cleavage and A(i) type cleavages of the reducing end GalNAcol, together with the non reducing end fragment from the loss of a single substituted GalNAcol. Substitution patterns on GlcNAc residues were also found, indicative for C-4 substitution ((0,2)A(i) - H(2)O cleavage) and disubstitution of C-3 and C-4 (Z(i)/Z(i) cleavages). This kind of fragmentation can be used for assigning the mode of chain elongation (Galbeta1-3/4GlcNAcbeta1-) and identification of Lewis type antigens like Lewis a/x and Lewis b/y on O-linked oligosaccharides. In essence, negative ion LC-MS(2) was able to generate extensive data for understanding the overall glycosylation pattern of a sample, especially when only a limited amount of material is available. 相似文献
993.
Investigation of sulfur release in ETV-ICP-AES and its application for the determination of sulfates 总被引:3,自引:0,他引:3
Antje Mroczek Gerhard Werner R. Wennrich Werner Schr?n 《Fresenius' Journal of Analytical Chemistry》1998,361(1):34-42
Electrothermal vaporization inductively coupled plasma atomic emission spectrometry was applied to the determination of sulfur
species in aqueous solutions. The sensitivity for sulfur as sulfate was found to be depending on the cations in the sample.
For understanding this phenomenon the thermal behavior of sulfuric acid, ammonium sulfate and the sulfates of sodium, zinc,
magnesium and silver was studied. There were significant differences in the thermal release of sulfur from these sulfates.
To explain these phenomena different reaction mechanisms were calculated using thermodynamic data. Pd(NO3)2 and Ge in KOH were successfully applied as modifiers for the stabilization of the sulfates during the thermal pre-treatment
step and to establish a uniform thermal behavior of different sulfates. The stabilization of sulfur using Ge and Pd as modifiers
is based on the reduction of the sulfates in presence of carbon, resulting in the formation of GeS and PdS, respectively.
This explanation has been supported by comparing the experimental results with thermodynamic calculations considering different
reactions for the thermal decomposition of the sulfates. Applying Ge (in KOH) as modifier the absolute detection limit was
300 pg sulfur (e.g. LOD 30 ng mL–1). The significant influence of phosphates on the determination of sulfur could be essentially reduced by Pd as modifier.
Received: 11 November 1997 / Revised: 14 January 1998 / Accepted: 18 January 1998 相似文献
994.
A case study is presented for the establishment of traceability for ammonium nitrogen determination in wastewater in a routine laboratory in order to fulfil the requirements of ISO/IEC standard 17025. The necessary relevant information was obtained from the method validation data, the quality control data and equipment calibration certificates. The method of measurement is described together with the measurement equation, selected traceable reference standards and the associated measurement uncertainty. The major sources of uncertainty of the result of measurement were identified and the combined uncertainty was calculated. Identification of the main uncertainty sources represents the basis for target operations for reducing the measurement uncertainty of this determination. 相似文献
995.
?zdemir ümmühan Karacan Nurcan ?entürk Ozan Sanlι Sert Sema U?ur Fadime 《Transition Metal Chemistry》2003,28(4):443-446
Five new complexes, [M(CO)5(apmsh)] [M = Cr; (1), Mo; (2), W; (3)], [Re(CO)4Br(apmsh)] (4) and [Mn(CO)3(apmsh)] (5) have been synthesized by the photochemical reaction of metal carbonyls [M(CO)6] (M = Cr, Mo and W), [Re(CO)5Br], and [Mn(CO)3Cp] with 2-hydroxyacetophenone methanesulfonylhydrazone (apmsh). The complexes have been characterized by elemental analysis, mass spectrometry, f.t.-i.r. and 1H spectroscopy. Spectroscopic studies show that apmsh behaves as a monodentate ligand coordinating via the imine N donor atom in [M(CO)5(apmsh)] (1–4) and as a tridentate ligand in (5). 相似文献
996.
Liu JM Hu SR He XM Li XL Zhan FP Zeng LQ Li LD Zhu GH Huang XM 《Analytical and bioanalytical chemistry》2005,382(7):1507-1512
Silicon dioxide nano-particles, diameter 50 nm, containing morin (morin–SiO2) have been synthesized by the sol–gel method. They emit strong and stable room-temperature phosphorescence (SS-RTP) on filter paper as substrate, and bismuth can quench the intensity of the SS-RTP. On this basis a new morin–SiO2 solid-substrate room-temperature phosphorescence-quenching method has been established for determination of traces of bismuth. Reduction of phosphorescence intensity (Ip) is directly proportional to the concentration of bismuth in the working range 0.16–14.4 ag spot–1 (sample volume 0.40 L spot–1, corresponding to the concentration range 0.40–36.0 fg mL–1). The regression equation of the working curve is Ip=14.86+5.279×[Bi3+] (ag spot–1) (n=6, r=0.9982). The detection limit of this method is 0.026 ag spot–1 (corresponding to a concentration of 6.5×10–17 g mL–1).This sensitive, reproducible and accurate method has been used for successful analysis of real samples. 相似文献
997.
We present a detailed study of the photophysical properties of a tetraphenoxy-substituted perylene bisimide derivative. The probe molecules were immobilized in a Shpol'skii matrix of hexadecane and investigated by single-molecule spectroscopy at cryogenic temperatures. By using single-molecule spectroscopic techniques we reveal the triplet substate kinetics and the fluorescence quantum yield, and we provide an estimate for the S1-S0 transition dipole moment. 相似文献
998.
A flow injection–capillary electrophoresis system with contactless conductivity detection and hydrostatic-pressure-generated flow was used for the fast and sensitive speciation of Se(IV) and Se(VI). The sample throughput was 25 samples per hour using a background electrolyte solution containing 8.75 mM l-histidine (His) adjusted to pH 4.00 with acetic acid. The repeatability of peak areas (n=8) was better than 1.41% and the limits of detection were 190 g L–1 and 7.5 g L–1 for Se(IV) and Se(VI), respectively. The interference from carbonate, typically present in water samples, was eliminated by using a low-pH electrolyte in which carbonate is uncharged and migrates at the EOF front. The method was applied to the analysis of Se(IV) and Se(VI) in soil samples that were spiked with both selenium species and the results for recovery of both selenium species were in good agreement with their introduced concentrations. 相似文献
999.
Size-related vaporisation and ionisation of laser-induced glass particles in the inductively coupled plasma 总被引:1,自引:0,他引:1
Ongoing discussions about the origin of elemental fractionation occurring during LA-ICP-MS analysis show that this problem is still far from being well understood. It is becoming accepted that all three possible sources (ablation, transport, excitation) contribute to elemental fractionation. However, experimental data about the vaporisation size limit of different particles in the ICP, as produced in laser ablation, have not been available until now. This information should allow one to determine the signal contributing mass within the ICP and would further clarify demands on suitable laser ablation systems and gas atmospheres in terms of their particle size distribution.The results presented here show a vaporisation size limit of laser induced particles, which was found at particle sizes between 90 nm and 150 nm using an Elan 6000 ICP-MS. Due to the fact that the ICP-MS response was used as evaluation parameter, vaporisation and ionisation limits are not distinguishable.The upper limit was determined by successively removing the larger particles from the aerosol, which was created by ablation of a NIST 610 glass standard at a wavelength of 266 nm, using a recently developed particle separation device. Various particle fractions were separated from the aerosol entering the ICP. The decrease in signal intensity is not proportional to the decrease in volume, indicating that particles above 150 nm in diameter are not completely ionised in the ICP. Due to the limited removal range of the particle separation device, which cannot remove particles smaller than 150 nm, single hole ablations were used to determine the lower vaporisation limit. This is based on measurements showing that larger particles occur dominantly during the first 100 laser pulses only. After this period, the ratio of ICP-MS counts and total particle volume was found to be constant while most of the particles are smaller than 90 nm, indicating complete vaporisation and ionisation of these particles.To describe the influence of different plasma forward powers on the vaporisation limit, the range 1000–1600 W was studied. Results indicate that optimum vaporisation and ionisation occurs at 1300 W. However, an increase of the particle ionisation limit towards larger particles was not observed within the accuracy of this study using the full range of parameters available for optimisation on commonly used ICP-MS instruments. 相似文献
1000.
Roberto?S.?Fernandes Gaspar?González Elizabete?F.?LucasEmail author 《Colloid and polymer science》2004,283(2):219-224
During oil production and treatment, oil-in-water (O/W) emulsions are formed. These dispersions require treatment prior to disposal. In order to improve oil/water separation processes through any physical process (decanting, flotation, centrifuging etc), the particle size of the dispersed phase should be increased. This may be obtained by a flocculation process, which consists in the agglomeration of several particles or drops using as flocculating agent hydrophilic high molecular weight macromolecules. Poly (ethylene-b-propylene oxide) and poly (vinyl alcohol) polymers have been evaluated as flocculating agents for oily water systems. Their performance is related to the particle size increase of the dispersed phase. In this work, a photometric dispersion analyzer (PDA) has been used to accomplish the oil drop agglomeration. Synthetic as well as produced water was used. Data are in good agreement with previous tests. Qualitative information related to aggregates or particle size distribution of the oily water systems can be obtained using PDA. 相似文献