Biomedical subjects

James H Barnes

Publications and source records attributed to James H Barnes.

9 recordsLinked to original sources

PubMed2006

Characterization of a second-generation focal-plane camera coupled to an inductively coupled plasma Mattauch-Herzog geometry mass spectrograph.

A second-generation Faraday-strip array detector has been coupled to an inductively coupled plasma Mattauch-Herzog geometry mass spectrograph, thereby offering simultaneous acquisition of a range of mass-to-charge ratios. The second-generation device incorporates narrower, more closely spaced collectors than the earlier system. Furthermore, the new camera can acquire signal on all collectors at a frequency greater than 2 kHz and has the ability to independently adjust the gain level of each collector. Each collector can also be reset independently. With these improvements, limits of detection in the hundreds of picograms per liter for metals in solution have been obtained. Some additional features, such as a broader linear dynamic range (over 7 orders of magnitude), greater resolving power (up to 600), and improved isotope ratio accuracy were attained. In addition, isotope ratio precision as low as 0.018% RSD was achieved.

Journal Article↗

PubMed2005

MS detectors.

Explore the source record for details and available documents.

Journal Article↗

PubMed2004

Simultaneous multichannel mass-specific detection for high-performance liquid chromatography using an array detector sector-field mass spectrometer.

The use of a separation step, such as liquid chromatography, prior to inductively coupled plasma mass spectrometry (ICP-MS) has become a common tool for highly selective and sensitive analyses. This type of coupling has several benefits including the ability to perform speciation analysis or to remove isobaric interferences. Several limitations of conventional instruments result from the necessity to scan or pulse the mass spectrometer to obtain a complete mass spectrum. When the instrument is operated in such a non-continuous manner, duty cycle is reduced, resulting in poorer absolute limits of detection. Additionally, with scanning instruments, spectral skew can be introduced into the measurement, limiting quantitation accuracy. To address these shortcomings, a high-performance liquid chromatograph has been coupled to an ICP-MS capable of continuous sample introduction and simultaneous multimass detection. These features have been realized with a novel detector array, the focal plane camera. Instrument performance has been tested for both speciation analysis and for the elimination of isobaric interferences. Absolute limits of detection in the sub picogram to tens of picograms regime are obtainable, while the added mass dimension introduced by simultaneous detection dramatically increases chromatographic peak capacity.

Arsenicals↗

PubMed2004

Characterization of a focal plane camera fitted to a Mattauch-Herzog geometry mass spectrograph. 2. Use with an inductively coupled plasma.

A novel charge-sensitive detector array, termed the focal plane camera (FPC), has been coupled to a Mattauch-Herzog mass spectrograph (MHMS) with an inductively coupled plasma ionization source. The FPC employs an array of gold Faraday cups, each with its own charge-integrating circuit that allows the simultaneous detection of several m/z ratios. The ion-sampling interface of the MHMS has been redesigned to provide better heat transfer away from the sampler and skimmer cones and to reduce the negative effects of turbulent gas flows around the plasma. The instrument has produced limits of detection in the tens to hundreds of parts per quadrillion regime and isotope ratio accuracy and precision of 5% error and 0.007% RSD, respectively. Limits of detection with the FPC are comparable to those obtained with a single-channel secondary electron multiplier (SEM). However, the isotope ratio accuracy and precision are better with the FPC than when the SEM is employed. The dynamic range has been shown to be linear over 7 orders of magnitude.

Journal Article↗

PubMed2004

Use of a novel array detector for the direct analysis of solid samples by laser ablation inductively coupled plasma sector-field mass spectrometry.

The use of laser ablation (LA) as a sample-introduction method for inductively coupled plasma mass spectrometry (ICP-MS) creates a powerful tool for trace elemental analysis. With this type of instrument, high analyte spatial resolution is possible in three dimensions with ng/g limits of detection and minimal sample consumption. Here, simultaneous detection is used to eliminate the correlated noise that plagues the ablation process. This benefit allows analyses to be performed with single laser pulses, resulting in improved depth resolution, even less sample consumption, and improved measurement precision. The new instrument includes an LA sample-introduction system coupled to an ICP ionization source and a Mattauch-Herzog mass spectrograph (MHMS) fitted with a novel array detector. With this instrument, absolute limits of detection are in the tens to hundreds of fg regime and isotope-ratio precision is better than 0.02% RSD with a one-hour integration period. Finally, depth-profile analysis has been performed with a depth resolution of 5 nm per ablation event.

Journal Article↗

PubMed2004

Development of an instrument to assess expectations of and preference for an insulin injection pen compared with the vial and syringe.

BACKGROUND: Before using a product, patients form expectations regarding the extent of a product's desirable attributes. These expectations can be used to understand their preference and anticipate potential satisfaction with the product. OBJECTIVE: The aim of this study was to produce a valid and reliable data collection instrument (the Insulin Injection Preference questionnaire [IIP-q]) to measure expectations of and preference for the insulin injection pen compared with the vial and syringe. METHODS: This study was initiated at the University of Mississippi (University, Mississippi). The IIP-q was developed to determine the extent to which respondents' prepurchase expectations of a product's attributes relate to preference for an insulin injection pen compared with the vial and syringe. Instrument development began with item generation related to product attributes important to patients who inject insulin. Items originated from an extensive search of the peer-reviewed Internet-based literature, marketing reports, clinical studies, and existing instruments. Content validity also was assessed using expert panel and focus group review. The resultant instrument (the IIP-q) was mailed to 1200 patients known to have type 1 or type 2 diabetes mellitus who either did or did not use insulin. Subscales were identified through exploratory factor analysis. Reliability and validity were assessed using Cronbach alpha for subscale items. Product-moment correlations between subscale dimensions and 2 global measures of preference were used to test the relationship between attribute expectations and preference. RESULTS: Seventeen of the questionnaires were returned as undeliverable, leaving 1183 in the sample population. Questionnaires were received from 302 individuals, 55 of whom failed to complete > or = 85% of the items and thus were not included in the final analysis. Of the 247 respondents (135 women, 112 men; mean [SD] age, 52.4 [13.2] years (range, 18-83 years]), 99 (40.1%) were current insulin users and 143 (57.9%) were not using insulin. Exploratory factor analysis resulted in a 13-item solution (Cronbach alpha = 0.92), accounting for 73.6% of the total explained variance. Ease of use, activity interference, and social acceptability emerged as expectation subscales from exploratory factor analysis. Cronbach alpha for items comprising the subscales ranged from 0.82 to 0.92. The 3 subscales were significantly correlated with patient preference (ease of use, r = 0.520, P < 0.001; activity interference, r = 0.570, p < 0.001; social acceptability, r = 0.602, p < 0.001). CONCLUSIONS: The results of the present study provide support for the IIP-q as a reliable and valid instrument to assess patient expectations of product attributes and preference. This instrument can be modified for use in clinical trials to determine the role of patient expectations and preference in their judgments regarding satisfaction with insulin delivery devices.

Cross-Sectional Studies↗

PubMed2003

Are our impressions of allergy test performances correct?

BACKGROUND: The clinical diagnosis is often subjective and susceptible to bias, yet it is the primary standard by which diagnostic tests are judged. Consequently, our opinions regarding various diagnostic tests may not be entirely accurate. OBJECTIVE: To investigate the accuracy of the clinical history compared with concordant skin and quantitative specific IgE (s-IgE) measurements. METHODS: Consecutive, consenting patients (N = 152) at 2 different allergy centers were examined by history and physical examination (HPE) alone to determine their sensitivity to 7 common allergens. Results were classified as positive, negative, or indeterminate. The HPE results were then compared to concordant skin prick testing (SPT) and s-IgE measurements and to quantitative IgE antibody measurements with and without knowledge of the SPT results. RESULTS: Diagnosis by HPE deviated considerably from concordant SPT and s-IgE results. This deviation differed between allergists and allergens, reflecting a positive HPE bias that averaged 22%. Seventy-six percent of the HPE results judged indeterminate were resolved as negative. Using additional information from the quantification of s-IgE antibodies, considerable differences between the sites in the level of s-IgE associated with a positive HPE result with and without SPT results were observed. CONCLUSIONS: Relative to the SPT and quantification of s-IgE antibodies, the diagnosis by HPE alone to common allergens is not consistent. Discrepancies were dependent on both allergen and allergist. The quantitative s-IgE data revealed that allergists use available information from the HPE and SPT differently. Since the HPE is the primary standard used in judging test efficacy (sensitivity and specificity), our current impressions of test performances are not likely to be accurate.

Adolescent↗

PubMed2002

Characterization of a focal plane camera fitted to a Mattauch-Herzog geometry mass spectrograph. 1. Use with a glow-discharge source.

A Mattauch-Herzog geometry mass spectrograph (MHMS) has been equipped with a novel array detector, the focal plane camera (FPC). The FPC consists of an array of gold Faraday cups, each coupled to its own integrator, with interrogation of the integrators performed by a multiplexer. The initial coupling of this instrument with a pin-type glow discharge source has provided limits of detection in the single to hundreds of nanograms per gram regime; isotope ratio accuracy and precision better than 5% error and 0.2% RSD, respectively; and a linear dynamic range of at least 6 orders of magnitude. A current weakness of the FPC is its pixel size, which limits both sensitivity and baseline resolution (to R = 130). The minimum data acquisition time for multiple images at present is 1 ms/image, with a dead time of 3.2 ms between images, which will limit the ability of the FPC to monitor extremely short transient signals.

Journal Article↗

PubMed2002

Incorporation of an electro-optic ion detector into an improved plasma-source mass spectrograph.

Throughout the history of mass spectrometry, array detectors have been used to conduct simultaneous and continuous mass-spectrographic studies. The benefits of acquiring multichannel data through the use of an array detector are well known and include greater duty cycle, improved precision through ratioing and internal-standardization techniques, and better quantitative analysis of fast signal transients. Because of these benefits, numerous types of array-detector-based instrumentation have been developed, including optical and mass spectrometers. Presented here is the improved performance of a plasma-source Mattauch-Herzog mass spectrograph fitted with a multichannel electro-optic ion detector. A glow-discharge source is used for all measurements. Previously reported array-detector-based data for this mass spectrograph were severely limited in quality and featured extremely poor peak shapes and resolution. Several figures of merit relevant to array detectors will be presented, including sensitivity, resolution, peak shape, and abundance sensitivity, all of which have been significantly improved. Remaining negative aspects of the array-detector performance include susceptibility to a magnetic field and the absence of uniform sensitivity across the array surface.

Electricity↗