Potential Sources Of Interference Research Articles

Polymerized coumaric acid as a model substrate for terrestrial-derived dissolved organic carbon utilized by aquatic microorganisms

It is now widely accepted that many surface waters receive more terrestrial carbon than assumed in the past, and that aquatic food webs are largely based on the supply of external dissolved organic carbon. However, very little information is available on how efficiently external carbon is utilized by microorganisms and transported to consumers of higher trophic levels. To address this issue, we prepared and tested polymers of 14C- p-coumaric acid (PCA) as a model substrate for terrestrial organic carbon. Photodegradation products that can be considered potential substrates for microorganisms were identified using hyphenated techniques, including gas chromatography-mass spectrometry (GC/MS) and ion chromatography-electrospray ionization mass spectrometry (IC/MS). Photolysis of PCA released monomeric phenol derivatives, e.g. 4-hydroxybenzaldehyde. The photolysis products observed were similar to those characteristic for natural organic carbon. Both a heterotrophic bacteria assemblage and a cultured algae strain exhibiting heterotrophic capabilities proved capable of utilizing the model substrate. Irradiation of PCA increased the uptake rate approximately eight times for the bacteria, but no significant increase was observed for the algae. Potential sources of interferences, e.g. the uptake of 14CO 2 released by photolysis, were addressed. It was concluded that PCA is a suitable substrate to study the metabolism of terrestrial DOC within aquatic communities.

A highly sensitive colorimetric microplate ferrocyanide assay applied to ascorbate-stimulated transplasma membrane ferricyanide reduction and mitochondrial succinate oxidation

Ferricyanide reduction frequently is analyzed to determine the activity of membraneous reductases. An improved, highly sensitive, and rapid method for quantitative endpoint determination of ferrocyanide is presented. Ferrocyanide is oxidized by Fe 3+ in the presence of Ferene-S under acid conditions to form a chromogenic Ferene-S/Fe 2+ complex. The latter is quantitated at 593 nm with a sensitivity of 33.2 mM −1 · cm −1. The assay is 60% more sensitive to ferrocyanide (and with a 50% lower detection limit) than the prevailing method of Avron and Shavit, which employs sulfonated bathophenanthroline as the ferrous chromogen. Both pH dependence and potential sources of interference are discussed. Using the method, a sulfhydryl-sensitive, ascorbate-stimulated transplasma membrane ferricyanide reductase was assayed in human chronic myeloid (K562) leukemia cells. Furthermore, malonate-sensitive succinate dehydrogenase activity of heart mitochondria was easily assayed with ferricyanide as terminal electron acceptor. The current method will suit routine applications demanding high throughput, robustness, and sensitivity in a 96-well plate format.

Determination of total trans fats and oils by infrared spectroscopy for regulatory compliance

The mandatory requirement in many countries to declare the amount of trans fat present in food products and dietary supplements has led to a need for sensitive and accurate methodologies for the rapid quantitation of total trans fats and oils. Capillary gas chromatography (GC) and infrared spectroscopy (IR) are the two methods most commonly used to identify and quantify trans fatty acids for food labeling purposes (see the article by Delmonte and Rader in this ABC issue for a detailed presentation of GC methodology). The present article provides a comprehensive review of the IR technique and the current attenuated total reflection (ATR) Fourier-transform (FT) IR methodologies for the rapid determination of total trans fats and oils. This review also addresses potential sources of interferences and inaccuracies in FTIR determinations, particularly those done at low trans levels. Recent observations have shown that the presence of saturated fats caused interferences in the FTIR spectra observed for trans triacylglycerols. The recognition and resolution of previously unresolved quantitative issues improved the accuracy and sensitivity of the FTIR methodology. Once validated, it is anticipated that the new negative second-derivative ATR-FTIR procedure will make IR spectroscopy more suitable than ever, and a rapid alternative and/or complementary method to GC, for the rapid determination of total trans fats for regulatory compliance. Figure Infrared light bouncing inside an internal reflection crystal.

Design and analysis of efficacy evaluation trials

Design and analysis of efficacy evaluation trials

Combination Detergent/MALDI Matrix: Functional Cleavable Detergents for Mass Spectrometry

This study reports the synthesis of the first functional cleavable detergent designed specifically for applications in mass spectrometry. Upon cleavage, two inert compounds and the MALDI matrix are formed, eliminating sources of potential interference originating from traditional cleavable detergents. Analysis of peptides demonstrates that MALDI matrix generated in situ results in MALDI spectra equivalent to those prepared using established protocols. Analysis of the membrane protein diacylglycerol kinase was accomplished using the combination detergent/MALDI matrix. Applications of the functional cleavable detergents to the profiling of whole cell lysates results in increased signal-to-noise ratios of many ions and the detection of additional proteins previously not observed.

Negative Interference in Cardiac Troponin I Immunoassays by Circulating Troponin Autoantibodies

There are numerous potential sources of interference in immunoassays. Our aim was to identify the blood component that causes negative interference in cardiac troponin I (cTnI) immunoassays based on antibodies against the central part of cTnI. We isolated an interfering factor (IF) from a sample with low recovery of added cTnI, using several consecutive purification steps: caprylic acid precipitation, ammonium sulfate precipitation, and purification on Cibacron Blue gel and protein G columns. Purified IF was identified by gel electrophoresis and mass spectrometric analysis of protein bands. For the direct detection of human antibodies to cardiac troponin in serum samples, we developed immunoassays using three different anti-human immunoglobulin antibodies and measured troponin antibodies in samples with low and normal cTnI recovery. Treatment with caprylic acid did not precipitate IF, but IF precipitated at 40% ammonium sulfate saturation. IF bound to a Cibacron Blue gel column, from which it was eluted with a linear salt gradient; it also bound to protein G. Gel electrophoresis of purified IF showed two major bands with molecular masses corresponding to the heavy (approximately 50 kDa) and light chains (approximately 25 kDa) of immunoglobulin, and their identities were confirmed by mass spectrometry. The presence of troponin-specific autoantibodies was confirmed in samples with low recoveries of cTnI by three different immunoassays. The median signals were significantly higher in 10 samples with low recovery than in 10 samples with normal recovery of cTnI (P < or = 0.007). Circulating autoantibodies to cTnI or other proteins of the troponin complex can be a source of negative interference in cTnI immunoassays.

The Potentiometric Effect of Hydrazine on a Belousov–Zhabotinskii Oscillating Chemical Reaction: Application to the Determination of Hydrazine

Abstract A method for determination of hydrazine based on the Belousov–Zhabotinskii reaction is proposed. The addition of the hydrazine to the oscillating system increases the oscillating amplitude. This increase in oscillating amplitude was used as the analytical signal. To obtain a maximum value of analytical signal in determination of the hydrazine, the effects of different concentrations of malonic acid, potassium bromide, potassium bromate, cerium(IV) and sulfuric acid were investigated and the optimum concentration of each component was used for further experiments. The analytical signal is linearly proportional to the logarithm of the hydrazine concentration over the range of 1 × 10−6 M to 1 × 10−3 M (1 M = 1 mol dm−3) under optimum conditions. The obtained LOD (2σ) was 1 × 10−6 M and the relative standard deviation (RSD) for five measurements of 1.1 × 10−4 M hydrazine was 5%. The influences of some potential sources of interference were also investigated.

Electromagnetically tracked guidewires for interventional procedures

We developed and tested a small electromagnetically tracked 5DOF bone screw. We examined accuracy compared to conventional optical tracking systems and developed devices and techniques for implanting the sensor during an interventional percutaneous procedure. Finally we conducted “proof-of-concept” experiments for percutaneous spine procedures by implanting the tracking sensors in the vertebral body of an interventional phantom and cadaver. Experiments were done in an interventional fluoroscopy suite to evaluate the susceptibility of the magnetic tracking system to potential interference sources in a hospital setting. Despite the presence of environmental metal, we were able track it robustly throughout the volume of interest. By using two or more of these screws, a rigid body reference definition was created. In image space, fiducials embedded in the screws were easily visualized on fluoroscopic images. Orientation errors of the new screw compared to the RCM-PAKY robot averaged 0.8° compared to 0.2° for the bare coil. Positioning error compared to the robot averaged 1.7 mm for the screw and 1.9 mm for the bare coil. Largest discrepancies occurred at the extremes of the volume. When using six DOF targets (employing two coils), positioning error averaged 1.5 mm. The magnetically tracked bone screw has good potential for reducing the invasiveness of many procedures that currently require separate registration and tracking. Accuracy is acceptable in the operating room, and the technique is not a major departure from current clinical practice.

Magnetically tracked bone screws for image guided intervention

We developed and tested a small electromagnetically tracked 5DOF bone screw. We examined accuracy compared to conventional optical tracking systems and developed devices and techniques for implanting the sensor during an interventional percutaneous procedure. Finally we conducted “proof-of-concept” experiments for percutaneous spine procedures by implanting the tracking sensors in the vertebral body of an interventional phantom and cadaver. Experiments were done in an interventional fluoroscopy suite to evaluate the susceptibility of the magnetic tracking system to potential interference sources in a hospital setting. Despite the presence of environmental metal, we were able track it robustly throughout the volume of interest. By using two or more of these screws, a rigid body reference definition was created. In image space, fiducials embedded in the screws were easily visualized on fluoroscopic images. Orientation errors of the new screw compared to the RCM-PAKY robot averaged 0.8° compared to 0.2° for the bare coil. Positioning error compared to the robot averaged 1.7 mm for the screw and 1.9 mm for the bare coil. Largest discrepancies occurred at the extremes of the volume. When using six DOF targets (employing two coils), positioning error averaged 1.5 mm. The magnetically tracked bone screw has good potential for reducing the invasiveness of many procedures that currently require separate registration and tracking. Accuracy is acceptable in the operating room, and the technique is not a major departure from current clinical practice.

Impurities from polypropylene microcentrifuge tubes as a potential source of interference in simultaneous analysis of multiple lipid-soluble antioxidants by HPLC with electrochemical detection.

High-performance liquid chromatography (HPLC) with electrochemical detection was used to analyze lipid-soluble antioxidants and micronutrients in plasma. Small amounts of plasma samples are often extracted in polypropylene (PP) microcentrifuge tubes before HPLC analysis due to its convenience. We therefore investigated the effect of impurities released from different PP tubes during extraction on the electrochemical detection of retinol, lutein, alpha-tocopherol, gamma-tocopherol, retinyl palmitate, beta-carotene and total coenzyme Q10 by an HPLC system with a coulometric array detector (CoulArray HPLC). An array of eight electrical potentials and gradient elution were applied. Human plasma or ultrapure water were extracted in four different PP tubes. Peaks at different retention times with varied amounts of unknown compounds were detected from different PP tubes. Although all those unknown peaks could be differentiated from peaks of interest by the CoulArray HPLC, they caused busy chromatographs, and one peak had an overlap with the dominant peak of lutein. Moreover, that peak completely masked the lutein peak when only one oxidizing potential was applied. Our results suggest potential interference from PP tubes on electrochemical detection especially when using only one electrical potential or having poor separation for these antioxidants if PP tubes are not carefully tested.

Interference in immunoassay is an underestimated problem.

The presence of antibodies in some patients' serum has long been known to be a potential source of interference in immunoassays, as shown by numerous case reports. These often appear after the introduction of a new analyte (e.g. troponin) and then decrease in number as the topic becomes exhausted. This highlights the persistent and intrinsic nature of this problem, despite attempts by the manufacturers to compensate for this source of error. However, an explanation of the immunoanalytical basis underpinning these assays could be more effective in raising awareness than intermittent case reports. In this review we have outlined the use of antibodies as reagents, the factors determining how they bind to antigen(s), and the nature of the immune response in order to explain the insidious and unpredictable nature of this form of interference. Studies on the prevalence of interference have yielded values ranging from 0.05 to more than 2%. However, these figures are analyte- and assay-specific, influenced by the study design, and are not therefore generally applicable. It is also highly likely that figures on prevalence and incidence will worsen in the future because of the wider use of monoclonal antibodies as diagnostic and therapeutic tools. Clinical laboratories should be alert to assay interference from antibodies irrespective of its nature, as immunoassays will remain an indispensable analytical tool, unlikely to be replaced in the foreseeable future by a practical alternative.

Radiofrequency Treatment of Hepatic Neoplasms in Patients With Permanent Pacemakers

Clinicians who provide care for patients with implantable devices for rhythm management, ie, pacemakers and internal cardioverter defibrillators, must be aware of sources of interference that could affect device function. Intracardiac radiofrequency is a recognized source of potential interference. However, radiofrequency to extracardiac sites that are relatively close to the implanted device has not been investigated thoroughly. We present 2 patients with permanent pacemakers undergoing intrahepatic radiofrequency for the treatment of metastatic disease. No interference was documented in either patient. Additional in vitro and in vivo studies are needed to determine definite clinical guidelines for such patients.

Radiofrequency Treatment of Hepatic Neoplasms in Patients With Permanent Pacemakers

Radiofrequency Treatment of Hepatic Neoplasms in Patients With Permanent Pacemakers

A new RT-PCR method for the identification of reoviruses in seawater samples

The frequent occurrence of reoviruses in environmental samples could be a potential source of interference with enterovirus detection, especially when enterovirus isolation on cell culture is required. In order to evaluate new virus-based criteria for enforcing recreational water quality standards, a new method based on a broad reverse transcribed polymerase chain reaction (RT-PCR) was set up to detect reoviruses. Two primers were engineered to amplify a 538 base pair fragment of the Sigma 2 gene. Reovirus strains obtained from ATCC (Jones, Lang, Dearing, Abney, NC-TEV, SV59 and SV12) were used as references. Twenty-four samples of 10 l were collected from two beaches of the Adriatic sea and 12 from the neighbourhood of Fano Harbour Channel. The presence of environmental reoviruses was tested on both concentrated seawater samples and lysates of BGM cells infected with the concentrated seawater samples. The new method was used in parallel with the detection of a 3 : 3 : 4 electrophoretic pattern of reovirus RNA in polyacrylamide gel electrophoresis (PAGE). Enterovirus and bacteria were also screened in compliance with EEC directives. No enteroviruses were isolated, and it was not attributable to reovirus interference. All the reovirus found by PAGE (8/72) were confirmed by RT-PCR, while several genomes (14/72) were detected only by RT-PCR. Presumptive methods of virus identification, that is CPE on BGM cells and haemagglutination test, were not able to detect them. The specificity of RT-PCR products was checked by direct nucleotide sequence analyses of the amplicons. The phylogenetic analyses showed heterogeneous taxa including human and animal reoviruses, with strong evidence that they were spreading consistently from the Harbour-Channel. This novel approach for reovirus detection will be very useful as a trace route of faecal pollution; more importantly, it could be very useful in contributing to the creation of a databank of circulating enteric viruses.

Spherical Mechanism Synthesis in Virtual Reality

This paper presents a new approach to using virtual reality (VR) to design spherical mechanisms. VR provides a three-dimensional (3-D) design space where a designer can input design positions using a combination of hand gestures and motions and view the resultant mechanism in stereo using natural head movement to change the viewpoint. Because of the three-dimensional nature of the design and verification of spherical mechanisms, VR is examined as a new design interface in this research. In addition to providing a VR environment for design, the research presented in this paper has focused on developing a “design in context” approach to spherical mechanism design. Previous design methods have involved placing coordinate frames along the surface of a constraint sphere. The new “design in context” approach allows a designer to freely place geometric models of movable objects inside an environment consisting of fixed objects. The fixed objects could either act as a base for a mechanism or be potential sources of interference with the motion of the mechanism. This approach allows a designer to perform kinematic synthesis of a mechanism while giving consideration to the interaction of that mechanism with its application environment.

Development of a flow injection analysis method for the determination of acrylamide copolymers in brines

Two primary methods are available for the measurement of polyacrylamide concentration in oilfield brines. One of these is a flow injection analysis (FIA) method based on the reaction of acrylamides with bromine (the starch–iodide method). The FIA method provides rapid sample throughput and high reproducibility, but may be sensitive to interferences or changes in the sample matrix. In this work, systematic optimization of the FIA method was conducted to improve analytical stability, reproducibility, and sensitivity. The effects of potential sources of interference from brines were examined in detail. These included Na +, Ca 2+, Cr 3+, Al 3+, Zr IV, NH 4 +, Cl −, OH −, CO 3 2− ions, sample coloration, and commonly used surfactants. Since the FIA method measures amide group concentration, the linearity of response for a series of partially hydrolysed polyacrylamides was measured. The range of the method is 2 to 1200 mg/l. Sample throughput is 30 samples/h with triplicate analysis. Relative standard deviations of 0.2% are readily obtained from standard solutions and 0.5% from complex samples (at 1000 mg/l).

International round robin tests on the measurement of carbon in diesel exhaust particulates.

Diesel soot has been recognized as probably carcinogenic to humans. Elemental carbon (also called black carbon) in soot is considered at the moment as the most significant surrogate to be measured for assessing the exposure to this pollutant. Its analysis is done by combustion in an oven and determination of the CO2 formed, after elimination of the organic fraction of the soot by heating and/or by solvent extraction. The analysis allows determination of both fractions of the soot: "elemental carbon" (EC) and organic carbon (OC). The sum of EC and OC is called TC (total carbon). An informal European coordination group organized two round robin tests on filter samples collected from diluted diesel emissions. The first round (RRT1) was performed on 13 different samples analyzed by ten laboratories. The range of loading was 2.5 to 150 micrograms/cm2 of EC. No evaluation of the precision within laboratories could be made since each laboratory gave only one result per sample. Therefore a second round (RRT2) was organized with two samples and a blank filter sent in several portions to 11 laboratories. It should be stressed that each laboratory used its own method and that no standardization was planned at this stage. Results of RRT1 showed that the coefficient of variation between laboratories decreased with higher loading and was around 10% to 15% for EC above about 20 micrograms/cm2. Dispersion of the results varied and it appeared that the way OC is removed from the soot is probably the most important factor of influence. The correlation between the laboratories was good as a whole but some systematic differences could be detected. Besides the different techniques to remove the organic carbon, the pretreatment of the filter by HCl (either as a vapor or as a solution) to remove the inorganic carbonates (potential interference sources), is probably also a significant factor of influence in the dispersion of the results between laboratories. It is not yet clear from these results whether the "environmental" laboratories give different results from the "occupational" laboratories, but it is clear that their objectives differ since for the "environmentalists", EC is not a specific marker of diesel emmissions, in contrast to the "occupationalists". It can be concluded that, although significant differences exist between laboratories they can be attributed mainly to the narrow distribution of the results within a single laboratory, and that the overall agreement of the results for EC and TC is fairly good. These results obtained with pure diesel engine emissions, should be complemented by field samples, but they have already achieved relevant findings in the performance of the procedures used to assess exposure to diesel soot.

Presence of third parties during neuropsychological evaluations: Who is evaluating whom?

Abstract State and federal laws and court decisions that address requests for the presence or absence of third party observers during forensic evaluations are reviewed, as are the legal arguments for both their inclusion and exclusion. Potential sources of interference created by observer's presence during the neuropsychological evaluation are outlined with reference to the Ethical Principles of Psychologists and Code of Conduct of the American Psychological Association, the Specialty Guidelines for Forensic Psychologists: Committee on Ethical Guidelines for Forensic Psychologists, and the Standards for Educational and Psychological Testing. The relevant empirical literature dealing with the phenomenon of social facilitation is also presented. Guidelines are offered for use by the neuropsychologist who receives a request for observation by a third party.

Electromagnetic interference from welding and motors on implantable cardioverter-defibrillators as tested in the electrically hostile work site

This study was designed to determine the susceptibility of an implanted cardioverter-defibrillator to electromagnetic interference in an electrically hostile work site environment, with the ultimate goal of allowing the patient to return to work. Normal operation of an implanted cardioverter-defibrillator depends on reliable sensing of the heart's electrical activity. Consequently, there is concern that external electromagnetic interference from external sources in the work place, especially welding equipment or motor-generator systems, may be sensed and produce inappropriate shocks or abnormal reed switch operation, temporarily suspending detection of ventricular tachycardia or ventricular fibrillation. The effects of electromagnetic interference on the operation of one type of implantable cardioverter-defibrillator (Medtronic models 7217 and 7219) was measured by using internal event counter monitoring in 10 patients operating arc welders at up to 900 A or working near 200-hp motors and 1 patient close to a locomotive starter drawing up to 400 A. The electromagnetic interference produced two sources of potential interference on the sensing circuit or reed switch operation, respectively: 1) electrical fields with measured frequencies up to 50 MHz produced by the high currents during welding electrode activation, and 2) magnetic fields produced by the current in the welding electrode and cable. The defibrillator sensitivity was programmed to the highest (most sensitive) value: 0.15 mV (model 7219) or 0.3 mV (model 7217). The ventricular tachycardia and ventricular fibrillation therapies were temporarily turned off but the detection circuits left on. None of the implanted defibrillators tested were affected by oversensing of the electric field as verified by telemetry from the detection circuits. The magnetic field from 225-A welding current produced a flux density of 1.2 G; this density was not adequate to close the reed switch, which requires approximately 10 G. Our testing at the work site revealed no electrical interference with this type of defibrillator. Patients were allowed to return to work. The following precautions should be observed by the patient: 1) maintain a minimal distance of 2 ft (61 cm) from the welding arc and cables or large motors, 2) do not exceed tested currents with the welding equipment, 3) wear insulated gloves while operating electrical equipment, 4) verify that electrical equipment is properly grounded, and 5) stop welding and leave the work area immediately if a therapy is delivered or a feeling of lightheadedness is experienced.

My memory of efforts in developing CCIR Recommendation 534-3: method for calculating sporadic-E field strength

Study Group 6 of the ITU Radio Communication Sector (ITU-R, formerly CCIR) deals with ionospheric propagation. The Study Group has twelve Recommendations, among which those recommending methods for calculating and predicting radio-signal strengths are the ones that telecommunications service providers need most. Rec. 534-3, concerning the method for calculating sporadic-E field strength, is one such Recommendation. Radio-wave propagation via the sporadic-E layer (Es) was expected, during the short-wave age, to be a possible communications medium. But today, it is treated as a potential source of interference with television signals, because of its irregular behavior. The progress in studies of Es propagation characteristics, and the existence of data banks of f/sub 0/Es data (f/sub 0/Es is the critical frequency of the ordinary wave in vertical-incidence radio sounding), obtained through worldwide observations, made it possible to construct a prediction method with worldwide applicability. The author describes the birth of the Recommendation, and the efforts made towards its realization.