Adoption of targeted mass spectrometry (MS) approaches such as multiple reaction monitoring (MRM) to study biological and biomedical questions is well underway in the proteomics community. Successful ...application depends on the ability to generate reliable assays that uniquely and confidently identify target peptides in a sample. Unfortunately, there is a wide range of criteria being applied to say that an assay has been successfully developed. There is no consensus on what criteria are acceptable and little understanding of the impact of variable criteria on the quality of the results generated. Publications describing targeted MS assays for peptides frequently do not contain sufficient information for readers to establish confidence that the tests work as intended or to be able to apply the tests described in their own labs. Guidance must be developed so that targeted MS assays with established performance can be made widely distributed and applied by many labs worldwide. To begin to address the problems and their solutions, a workshop was held at the National Institutes of Health with representatives from the multiple communities developing and employing targeted MS assays. Participants discussed the analytical goals of their experiments and the experimental evidence needed to establish that the assays they develop work as intended and are achieving the required levels of performance. Using this “fit-for-purpose” approach, the group defined three tiers of assays distinguished by their performance and extent of analytical characterization. Computational and statistical tools useful for the analysis of targeted MS results were described. Participants also detailed the information that authors need to provide in their manuscripts to enable reviewers and readers to clearly understand what procedures were performed and to evaluate the reliability of the peptide or protein quantification measurements reported. This paper presents a summary of the meeting and recommendations.
The degradation and mobility of sulfometuron-methyl and potential degradates were evaluated under actual field conditions in the United States following application of Oust herbicide to bare ground ...at the maximum labeled rate. Sulfometuron-methyl degraded rapidly at the four test sites; calculated half-life (t 1/2) values ranged from 12 to 25 days. Sulfometuron-methyl residues were below the limit of quantitation (10 ppb) beyond 90 days after treatment (DAT) at all test sites. The highest degradate concentration present at the end of the study (359 DAT) was 40 ppb (the herbicidally inactive 2-amino-4,6-dimethylpyrimidine). Sulfometuron-methyl and its degradates were immobile under field conditions. Keywords: Sulfometuron-methyl; degradation; mobility; half-life; soil
Mass Spectrometry in Trace Analysis Bethem, Robert A; Boyd, Robert K
Journal of the American Society for Mass Spectrometry,
06/1998, Letnik:
9, Številka:
6
Journal Article
Recenzirano
Odprti dostop
This report is an opinion piece arising from the response to the 1996 ASMS Fall Workshop “Limits to Confirmation, Quantitation, and Detection.” The two subjects that generated the most heated ...discussion at the Workshop were the criteria for qualitative confirmation of target analytes and those for defining and measuring limits of detection and of quantitation. A reportorial account of the Workshop has been published previously (Baldwin, R.; et al.
J. Am. Soc. Mass Spectrom. 1997,
8, 1180–1190). The purpose of the present work is to (1) attempt to reconcile the sometimes highly divergent views expressed by some of the invited Workshop speakers and (2) provide some impetus toward a consensus approach to the dual problems of analyte identification and operational definitions of limits of detection and quantitation for application to trace analysis using chromatography with mass spectrometric detection. In view of the wide range of analytical problems dealt with by modern mass spectrometrists and the varied contexts in which these activities are undertaken (including regulatory requirements and possible legal challenges), both issues are addressed using the concept of fitness for purpose. It is proposed that an appropriate goal is not to define a set of universally applicable criteria, but rather to recommend guidelines for establishing integrated analytical methods best suited to the particular purpose and context.
This report is submitted by a working group sponsored by the ASMS Measurements and Standards Committee. The group responded to a 1998 opinion piece dealing with mass spectrometry in trace analysis ...(Bethem, R. A.; Boyd, R. K.
J. Am. Soc. Mass Spectrom.
1998,
9, 643–648) which proposed that the concept of
fitness for purpose addresses the needs of a wide range of analytical problems. There is a need to define
fitness for purpose within the current context of mass spectrometry and to recommend processes for developing and evaluating methods according to suitability for a particular purpose. The key element in our proposal is for the interested parties to define in advance the acceptable degree of measurement uncertainty and the desired degree of identification confidence. These choices can serve as guideposts during method development and targets for retrospective evaluation of methods. A series of more detailed recommendations are derived from basic principles and also from reviews of current practice. This report highlights some areas where consensus is evident, but also revealed the need for further work in other areas. The recommendations are aimed primarily for the laboratory analyst but we hope they will be accessible to the non-scientist as well. Our goal was to provide a framework that can support informed decisions and foster discussion of the issues, because ultimately it is the responsibility of the analyst to make choices, provide supporting data, and interpret results according to scientific principles and qualified judgment.
Dapsone is a potent anti-inflammatory and antibacterial agent that has been used extensively in the oral treatment of leprosy and dermatitis herpetiformis. This study compared the pharmacokinetic ...profile of dapsone in rats given a single oral or i.v. 12 mg/kg dose (n = 8/group) or a single dermal application of 12 or 60 mg/kg (n = 12/group) in an aqueous gel application medium containing 10 or 25% diethylene glycol monoethyl ether (DGME). Blood samples (200 microl) were collected via tail vein from each rat and pooled at intervals up to the 24-h period. A terminal blood sample was collected by cardiac puncture from each animal. Plasma concentrations of dapsone were determined by liquid chromatography atmospheric pressure ionization tandem mass spectroscopy. There was no treatment-related overt toxicity observed in any of the animals. Peak levels were reached 1 h after oral dosing (4890 ng/ml), and 6 to 8 h after dermal application, with Cmax values of 1.62, 5.56, and 12.8 ng/ml, for 12 mg/kg at 10 or 25% DGME, and for 60 mg/kg at 25% DGME, respectively. Bioavailability was calculated at 78% after oral dosing and <1% after dermal application. Apparent elimination half-lives (t(1/2))s were similar after i.v. and oral dosing. Both the calculated area under the plasma concentration versus time curve up to 24 h and Cmax values were 3- to 4-fold higher in the dermal application group administered 12 mg/kg dapsone in 25 versus 10% DGME gel, whereas the calculated area under the plasma concentration versus time curve up to 24 h and Cmax values for the 60 mg/kg group were only 3.3- and 2.3-fold greater than those obtained after application of 12 mg/kg in 25% DGME. These results show that both systemic exposure and peak plasma concentrations of dapsone are minimized by dermal versus oral administration of the compound.
This paper describes the characterization of glucuronide and sulfuric acid conjugates and alkyl phosphates by thermospray tandem mass spectrometry (MS/MS). Primary thermospray mass spectra were ...generated using ammonium acetate buffer and filament-on ionization with both positive and negative ion detection. In positive ion mode molecular weight information was obtained for glucuronic, phosphoric and other weak acids. Under these conditions, however, spectra were not obtained for the sulfate adducts or phosphate salts. Negative ion thermospray mass spectrometry was more versatile, providing spectra of all metabolic structures examined. Positive and negative ion mass spectra provided complementary information for glucuronic acids. Collisionally activated dissociation (CAD) mass spectra of the glucuronide M + NH4+ or M - H- ions exhibited characteristic glucuronide 'fingerprints' as well as prominent aglycone ions. The aryl sulfates were hydrolyzed to the corresponding phenols under buffer/thermospray conditions and for these analytes CAD mass spectra were obtained from phenate- or phenol + acetate- parent ions. The M- of dimethyl thiophosphate underwent sequential loss of alkyl and alkoxy radicals and formaldehyde with collisional activation. MS/MS greatly enhances the power of the thermospray interface by providing fragmentation information useful both in the identification of unknowns and for improved mass spectrometry specificity.
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