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  • LC/MS/MS structure elucidation of reaction intermediates formed during the TiO2 photocatalysis of microcystin-LR 18377943

    Microcystin-LR (MC-LR), a cyanotoxin and emerging drinking water contaminant, was treated with TiO2 photocatalysts immobilized on stainless steel plates as an alternative to nanoparticles in slurry. The reaction intermediates of MC-LR were identified with mass spectrometry (MS) at pH of Milli-Q water (pHsq = 5.7). Eleven new [M+H]+ were observed in the liquid chromatography mass spectrometry (LC/MS) chromatogram with some of them giving multiple peaks. Most of these reaction intermediates have not been reported from previous studies employing TiO2 nanoparticles at acidic conditions (pH = 4.0). Investigating the effects of pH (for 3.0ms showed that acidic conditions are preferable for the degradation. Combined with the limited surface area of the films and the absence of additional oxidants (i.e., H2O2) the degradation was slower and more intermediate steps were identified. Possible structures of the intermediates (formed at neutral pH) after analyzing the corresponding MS/MS spectra are reported. The collision-induced dissociation of the [M+H]+ of MC-LR and the intermediates 1011.5 and 1029.5 are discussed and possible fragmentation pathways and mechanisms are also proposed. Analysis of the MS/MS spectra indicates that the fragmentation of some amino acids is less favorable because of internal interaction with free groups of adjacent amino acids. The MS/MS spectra assisted in determining hydroxylation sites, by the formation or alteration of specific product ions such as m/z 599.
    Document Type:
    Reference
    Product Catalog Number:
    Multiple

  • Large-scale quantitative LC-MS/MS analysis of detergent-resistant membrane proteins from rat renal collecting duct. 18596208

    In the renal collecting duct, vasopressin controls transport of water and solutes via regulation of membrane transporters such as aquaporin-2 (AQP2) and the epithelial urea transporter UT-A. To discover proteins potentially involved in vasopressin action in rat kidney collecting ducts, we enriched membrane "raft" proteins by harvesting detergent-resistant membranes (DRMs) of the inner medullary collecting duct (IMCD) cells. Proteins were identified and quantified with LC-MS/MS. A total of 814 proteins were identified in the DRM fractions. Of these, 186, including several characteristic raft proteins, were enriched in the DRMs. Immunoblotting confirmed DRM enrichment of representative proteins. Immunofluorescence confocal microscopy of rat IMCDs with antibodies to DRM proteins demonstrated heterogeneity of raft subdomains: MAL2 (apical region), RalA (predominant basolateral labeling), caveolin-2 (punctate labeling distributed throughout the cells), and flotillin-1 (discrete labeling of large intracellular structures). The DRM proteome included GPI-anchored, doubly acylated, singly acylated, cholesterol-binding, and integral membrane proteins (IMPs). The IMPs were, on average, much smaller and more hydrophobic than IMPs identified in non-DRM-enriched IMCD. The content of serine 256-phosphorylated AQP2 was greater in DRM than in non-DRM fractions. Vasopressin did not change the DRM-to-non-DRM ratio of most proteins, whether quantified by tandem mass spectrometry (LC-MS/MS, n=22) or immunoblotting (n=6). However, Rab7 and annexin-2 showed small increases in the DRM fraction in response to vasopressin. In accord with the long-term goal of creating a systems-level analysis of transport regulation, this study has identified a large number of membrane-associated proteins expressed in the IMCD that have potential roles in vasopressin action.
    Document Type:
    Reference
    Product Catalog Number:
    05-184

  • GEL-FREE SAMPLE PREPARATION FOR THE NANOSCALE LC-MS/MS ANALYSIS AND IDENTIFICATION OF LOW-NANOGRAM PROTEIN SAMPLES 17763504

    Protein identification at the low nanogram level could in principle be obtained by most nanoscale LC-MS/MS systems. Nevertheless, the complex sample preparation procedures generally required in biological applications, and the consequent high risk of sample losses, very often hamper practical achievement of such low levels. In fact, the minimal amount of protein required for the identification from a gel band or spot, in general, largely exceeds the theoretical limit of identification reachable by nanoscale LC-MS/MS systems. A method for the identification of low levels of purified proteins, allowing limits of identification down to 1 ng when using standard bore, 75 microm id nanoscale LC-MS/MS systems is here reported. The method comprises an offline two-step sample cleanup, subsequent to protein digestion, which is designed to minimize sample losses, allows high flexibility in the choice of digestion conditions and delivers a highly purified peptide mixture even from "real world" digestion conditions, thus allowing the subsequent nanoscale LC-MS/MS analysis to be performed in automated, unattended operation for long series. The method can be applied to the characterization of low levels of affinity purified protei
    Document Type:
    Reference
    Product Catalog Number:
    C5737
    Product Catalog Name:
    ZipTip® Pipette Tips

  • Evaluation of HPLC reagent water purity via LC-MS and total organic carbon analysis Evaluation of HPLC reagent water purity via LC-MS and total organic carbon analysis

    An important factor in optimizing LC-MS analysis is the use of solvents and chemical reagents of high purity. When converting from HPLC with UV detection to LCMS, the purity of water used for the mobile phase becomes critical. In addition to column blinding, ghost peaks, and other problems caused by excess organics in HPLC, organic contamination creates high background and causes a loss of sensitivity in LC-MS. Although confirmation via MS-MS, for example, would be required for precise identification of species detected in the water,2 the presence and magnitude of the selected spectra reasonably indicate the relative purity of these waters. This was particularly visible when using bottled HPLC-reagent waters. Analysis of HPLC-grade water using UV detection at 214 and 254 nm is not a suitable quality control for LC-MS applications. On-line measurement of organics as TOC appears to provide a rapid and timely indication of the organic purity of water suitable to successfully perform LC-MS. Additionally, ion exchange combined with UV photooxidation offers a benefit to LC-MS users over conventional water systems that use ion-exchange media alone. The observations and methods used may provide a screening method to monitor the quality of reagent waters used in HPLC and LC-MS in order to obtain optimal results.
    Document Type:
    Reference
    Product Catalog Number:
    Multiple
    Product Catalog Name:
    Multiple