Quadrupole mass filter operation under the influence of magnetic field

This work demonstrates resolution enhancement of a quadrupole mass filter (QMF) under the influence of a static magnetic field. Generally, QMF resolution can be improved by increasing the number of rf cycles an ion experiences when passing through the mass filter. In order to improve the resolution, the dimensions of the QMF or the operating parameters need to be changed. However, geometric modifications to improve performance increase the manufacturing cost and usually the size of the instrument. By applying a magnetic field, a low-cost, small footprint instrument with reduced power requirements can be realized. Significant improvement in QMF resolution was observed experimentally for certain magnetic field conditions, and these have been explained in terms of our theoretical model developed at the University of Liverpool. This model is capable of accurate simulation of spectra allowing the user to specify different values of mass spectrometer dimensions and applied input signals. The model predicts enhanced instrument resolution R>26,000 for a CO2 and N2 mixture with a 200-mm long mass filter operating in stability zone 3 via application of an axial magnetic field.

Quadrupole mass filter: design and performance for operation in stability zone 3

The predicted performance of a quadrupole mass filter (QMF) operating in Mathieu stability zone 3 is described in detail using computer simulations. The investigation considers the factors that limit the ultimate maximum resolution (Rmax) and percentage transmission (%Tx), which can be obtained for a given QMF for a particular scan line of operation. The performance curve (i.e., the resolution (R) versus number (N) of radio frequency (rf) cycles experienced by the ions in the mass filter) has been modeled for the upper and lower tip of stability zone 3. The saturation behavior of the performance curve observed in practice for zone 3 is explained. Furthermore, new design equations are presented by examining the intersection of the scan line with stability zone 3. Resolution versus transmission characteristics of stability zones 1 and 3 are compared and the dependence of performance for zones 1 and 3 is related to particular instrument operating parameters.

Mapping the stability diagram of a quadrupole mass spectrometer with a static transverse magnetic field applied

Previous experimental and theoretical work identified that the application of a static magnetic (B) field can improve the resolution of a quadrupole mass spectrometer (QMS) and this simple method of performance enhancement offers advantages for field deployment. Presented here are further data showing the effect of the transverse magnetic field upon the QMS performance. For the first time, the asymmetry in QMS operation with B x and B y is considered and explained in terms of operation in the fourth quadrant of the stability diagram. The results may be explained by considering the additional Lorentz force (v x B) experienced by the ion trajectories in each case. Using our numerical approach, we model not only the individual ion trajectories for a transverse B field applied in x and y but also the mass spectra and the effect of the magnetic field upon the stability diagram. Our theoretical findings, confirmed by experiment, show an improvement in resolution and ion transmission by application of magnetic field for certain operating conditions.

A method of computing accurate 3D fields of a quadrupole mass filter and their use for prediction of filter behavior

A method is described that enables the three-dimensional fields of a simple quadrupole mass filter (QMF) to be determined to a high accuracy. The technique produces accurate field values in the fringe field region as well as in the center of the filter. Using fields obtained typical filter performance is determined and shown to differ from that predicted when fringe fields are ignored. The computed performance shows features obtained experimentally and displays more complex variation with ion mass and other parameters than when fringe fields are ignored.

The mycotoxin patulin increases colonic epithelial permeability in vitro

The gastrointestinal lumen is directly exposed to dietary contaminants, including patulin, a mycotoxin produced by moulds. Patulin is known to increase permeability across intestinal Caco-2 monolayers. This study aimed to determine the effect of patulin on permeability, ion transport and morphology in isolated rat colonic mucosae. Mucosal sheets were mounted in Ussing chambers and voltage clamped. Apical addition of patulin (100-500 μM) rapidly reduced transepithelial electrical resistance (TEER) and increased permeability to [(14)C] mannitol (2.9-fold). Patulin also inhibited carbachol-induced electrogenic chloride secretion and histological evidence of mucosal damage was observed. To examine potential mechanisms of action of patulin on colonic epithelial cells, high-content analysis of Caco-2 cells was performed and this novel, quantitative fluorescence-based approach confirmed its cytotoxic effects. With regard to time course, the cytotoxicity determined by high content analysis took longer than the almost immediate reduction of electrical resistance in isolated mucosal sheets. These data indicate patulin is not only cytotoxic to enterocytes but also has the capacity to directly alter permeability and ion transport in intact intestinal mucosae. These data corroborate and extend findings in intestinal cell culture monolayers, and further suggest that safety limits on consumption of patulin may be warranted.

Can patients with dementia be assessed at a distance? The use of Telehealth and standardised assessments

BACKGROUND

Telehealth could be a medium for the provision of cognitive assessments to distant sites.

AIMS

The aims of the present study were to determine the interrater reliability of the Standardized Mini Mental State Exam (SMMSE) and the Geriatric Depression Scale (GDS) through Telehealth as compared to face-to-face administration.

METHODS

Duplicate interviews of subjects with crossover of interview modality were carried out. Twenty patients were interviewed between two sites 11 km apart. Subjects were persons older than 65 years (mean age 82 years) who consented to Telehealth assessments. The outcome measures were the differences in assessment scores between the two media.

RESULTS

The average SMMSE score by remote assessment was 24.0 (range 11.0-30.0) and by direct assessment was 24.3 (range 9.0-30.0). The correlation between direct and remote SMMSE scores was 0.90. The mean difference between direct and remote SMMSE scores was -0.3 (95% confidence interval (CI): -4.6 to 4.0). In 8 of 20 participants (40%) the difference between Telehealth and direct assessments was two points or more on the SMMSE. The average GDS by remote assessment was 6.1 (range 1.0-14.0) and by direct assessment was 5.8 (range 2.0-13.0). The correlation between direct and remote GDS scores was 0.78. The mean difference between direct and remote GDS assessment was 0.3 (95% CI: -3.8 to 4.4).

CONCLUSION

Remote assessments with SMMSE and GDS using Telehealth methods yielded similar results to direct assessments. However, there was a moderate difference between face-to-face and Telehealth assessments in some subjects, which could influence clinical decision-making.

Data mining methods find demographic predictors of preterm birth

BACKGROUND

Preterm births in the United States increased from 11.0% to 11.4% between 1996 and 1997; they continue to be a complex healthcare problem in the United States.

OBJECTIVE

The objective of this research was to compare traditional statistical methods with emerging new methods called data mining or knowledge discovery in databases in identifying accurate predictors of preterm births.

METHOD

An ethnically diverse sample (N = 19,970) of pregnant women provided data (1,622 variables) for new methods of analysis. Preterm birth predictors were evaluated using traditional statistical and newer data mining analyses.

RESULTS

Seven demographic variables (maternal age and binary coding for county of residence, education, marital status, payer source, race, and religion) yielded a .72 area under the curve using Receiving Operating Characteristic curves to test predictive accuracy. The addition of hundreds of other variables added only a .03 to the area under the curve.

CONCLUSION

Similar results across data mining methods suggest that results are data-driven and not method-dependent, and that demographic variables offer a small set of parsimonious variables with reasonable accuracy in predicting preterm birth outcomes in a racially diverse population.

Building knowledge in a complex preterm birth problem domain

Data mining methods used a racially diverse sample (n = 19,970) of pregnant women and 1,622 variables that were collected in Duke's TMR electronic patient record over a 10-year period. Different statistical and data mining methods were similar when compared using receiver operating characteristic (ROC) curves. Best results found that seven demographic variables yielded .72 and addition of hundreds of other clinical variables added only .03 to the area under the curve (AUC). Similar results across methods suggest that results were data-driven and not method-dependent, and that demographic variables may offer a small set of parsimonious variables with predictive accuracy in a racially diverse population. Work to determine relevant variables for improved predictive accuracy is ongoing.

Has behavior therapy drifted from its experimental roots? A survey of publication trends in mainstream behavioral journals

In recent years it has been suggested that behavior therapy, characterized in part by single-subject designs and an idiographic approach to addressing practical problems, is drifting from its experimental roots. To examine trends in behavior therapy, and to provide an objective index of drift, two archival studies were conducted to identify publication trends in the use of single-subject designs vs. group designs, as well as citations to select basic behavioral science journals. In Study 1, articles appearing in Behavior Therapy from 1970 through 1996 were reviewed and categorized in terms of type of article, design, and citations to experimental journals. Findings from Study 1 suggest declining publication trends in single-subject designs and citations to experimental journals in Behavior Therapy, with a modest increase in the use of group designs over the period. Study 2 was designed to replicate and extend our initial findings by surveying three behavioral journals in addition to Behavior Therapy using the PsychLit database and years covering 1974 through 1996: Behaviour Research and Therapy, Journal of Behavior Therapy and Experimental Psychiatry, and Behavior Modification. Consistent with Study 1, results of Study 2 showed declining trends in single-subject designs for all mainstream behavioral journals. The significance of these findings in light of the argument that behavior therapy has drifted from its experimental roots is discussed, with emphasis on contingencies that may be responsible for the trends observed.