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PubMed2005

A rapid and sensitive analysis of diphenylarsinic acid in water by gas chromatography/mass spectrometry.

A rapid and sensitive analytical method using pentafluorothiophenol (PFTP) derivatization was applied to detect diphenylarsinic acid (DPAA) in water. In this study, the optimum derivatization conditions, such as acid concentration, reaction time and reaction temperature, were investigated to develop a suitable procedure for DPAA determination. After extracting the derivatives into benzene, the determination was carried out by gas chromatography/mass spectrometry (GC/MS) with selected ion monitoring (SIM). The detection limit of the method was 9.4 microg/l, and the overall recoveries obtained from real environmental samples were 88.9 - 104.7% and coefficient variations were 5.1 - 13.9%.

Arsenicals↗
PubMed2006

Decentred comparative research: Context sensitive analysis of maternal health care.

Cross-national comparison is an important tool for health care research, but too often those who use this method fail to consider important inter-national differences in the social organisation of health care and in the relationship between health care practices and social experience. In this article we make the case for a context-sensitive and reflexive analysis of health care that allows researchers to understand the important ways that health care systems and practices are situated in time and place. Our approach--decentred comparative research--addresses the often unacknowledged ethnocentrism of traditional comparative research. Decentred cross-national research is a method that draws on the socially situated and distributed expertise of an international research team to develop key concepts and research questions. We used the decentred method to fashion a multilevel framework that used the meso level of organisation (i.e., health care organisations, professional groups and other concrete organisations) as an analytical starting point in our international study of maternity care in eight countries. Our method departs from traditional comparative health systems research that is most often conducted at the macro level. Our approach will help researchers develop new and socially robust knowledge about health care.

Delivery of Health Care↗
PubMedDate not supplied

[Sensitivity analysis in health investment projects].

This paper discusses some of the concepts and methodologies frequently used in sensitivity analyses in the evaluation of investment programs. In addition, a concrete example is presented: a hospital investment in which four indicators were used to design different scenarios and their impact on investment costs. This paper emphasizes the importance of this type of analysis in the field of management of health services, and more specifically in the formulation of investment programs.

Cost-Benefit Analysis↗
PubMed2002

Simultaneous and sensitive analysis of Cu, Ni, Zn, Co, Mn, and Fe in food and biological samples by ion chromatography.

A sensitive and simple method for the simultaneous determination of nutritionally important minerals in food samples is in great demand. Ion chromatography coupled with UV-vis detection is shown to be an appropriate technique for this objective. The method is based on the formation of mineral complexes by pyridine-2,6-dicarboxylic acid in the mobile phase. The complexes are then postcolumn derivatized with 4-(2-pyridylazo)resorcinol (PAR), resulting in mineral-PAR complexes that are detected by UV-vis absorption at 500 nm. This facilitates the simultaneous separation and quantification of minerals in one chromatographic run. Within 16 min, Cu, Ni, Zn, Co, Mn, and Fe are analyzed. When a 50 microL injection volume is used, the average detection limit is 5 ppb in the injection liquid. The detection limit makes it a superior alternative to AAS and, in several applications, also an alternative to ICP-MS techniques. Different sample treatments were evaluated. The concentration of acid in the treated sample varied with the sample treatment, which may cause a limitation for the injection volume. A crucial prerequisite to achieve the reported detection limits and to obtain reliable results is to completely exclude all contamination from instruments and materials.

Calibration↗
PubMed1975

Sensitive analysis of ethanolamine- and serine-containing phosphoglycerides by high-performance liquid chromatography.

A highly sensitive method for the separation and quantitative measurement of phospholipids containing primary amino groups, such as phosphatidylethanolamine, phosphatidylserine and lysophosphatidylethanolamine, is described. The method involves a simple and quantitative derivative formation of the phospholipids containing amino groups to their u.v.-absorbing biphenylcarbonyl derivatives. These have molar extinction coefficients of about 23,000 at 268nm. The phospholipid derivatives are then separated and non-destructively determined by high-performance liquid chromatography. The amino phospholipids containing vinyl ether bonds (plasmalogens) can be determined separately from the diacyl- and alkylacyl-amino phospholipids. The lower limit of detection by high-performance liquid-chromatographic analysis of the phospholipid derivatives is about 10-13pmol or 0.3-0.4ng of phospholipid P. The quantitative range of derivative formation and analysis by high-performance liquid chromatography of the phospholipids containing amino groups was shown to be 10-500nmol. The method was shown to be applicable to the analysis of phospholipids containing amino groups in tissue samples.

Biphenyl Compounds↗
PubMed1997

High-sensitivity analysis of neutral underivatized oligosaccharides by nanoelectrospray mass spectrometry.

Nanoscale electrospray ionization (nano-ESI) overcomes the sensitivity problems found and reported for neutral oligosaccharides in conventional microscale forced-flow ESI. For a series of compounds ranging from trisaccharides to larger polymers with molecular masses up to 6 kDa, sample concentrations of 10(-5) M, i.e., 10 pmol total sample load, yielded very intense singly or multiply cationized molecule ions in an ion-trap mass spectrometer. In a dilution series, it is exemplified that, at the 10(-8) M level, molecule ion signals can be clearly registered with a S/N ratio of about 7. Only 100 amol of sample has been consumed in this experiment. Investigation of an oligosaccharide-peptide mixture revealed that the oligosaccharide is suppressed in conventional ESI, whereas in nano-ESI both analytes are detected at comparable and high intensities. Mechanistic implications are discussed, emphasizing the influence of surface activity for the two ESI techniques. The very low flow rates inherent to nano-ESI of about 30 nL/min, together with the high signal intensity, make it possible to fully employ the MSn capabilities of an ion-trap mass spectrometer for structural analysis. From less than 1 microL of sample solution it is possible to make consecutive fragmentation experiments up to MS7 to obtain valuable information about the structure of complex oligosaccharides.

Mass Spectrometry↗
PubMed1999

Comparison of ventricular pressure relaxation assessments in human heart failure: quantitative influence on load and drug sensitivity analysis.

OBJECTIVES: We contrasted various methods for assessing ventricular pressure decay time constants to test whether sensitivity to slight data instability or disparities between model-assumed and real decay are systematically altered by cardiac failure. We hypothesized that such discrepancies could result in apparent increased relaxation sensitivity to load and drug stimulation. BACKGROUND: Deviation of relaxation behavior from model-assumed waveforms may be worsened by failure, enhancing instability and apparent load and drug sensitivity of commonly used indexes. METHODS: Pressure-volume relations were measured in patients with normal (n = 14), hypertrophic (hypertrophic cardiomyopathy [HCM], n = 15) and dilated-myopathic (dilated cardiomyopathy [DCM], n = 37) hearts before and during preload reduction or inotropic stimulation. Relaxation parameters (monoexponential [ME] model assuming zero-T(in) or non-zero-T(D), T(F) asymptote:, hybrid logistic-T(L), linear-T(LR), and pressure halftime-T(1/2)) were contrasted regarding sensitivity to slight data range manipulation and loading or drug changes. RESULTS: In DCM, T(D) and T(F) prolonged 15% to 25% (p < 0.0001) by deletion of only 1-2 data points, whereas this had minimal effect on controls or HCM. This stemmed from systematic deviation of relaxation from an ME decay in DCM. T(1/2) and T(in) were highly sensitive to pure pressure offsets, whereas T(L) was most stable to both manipulations in all hearts. As a result, T(D) and T(F) appeared to be much more sensitive to systolic load in DCM than T(1/2) or T(L) and disproportionately sensitive to increased cyclic adenosine monophosphate (cAMP). CONCLUSIONS: Relaxation consistently deviates from an ME decay in DCM resulting in instability and amplified relaxation systolic load or drug dependence of ME-based indexes in failing versus control (or HCM) hearts. The hybrid-logistic method improves quantitative analyses by providing more consistent data fits with all three heart types.

Adult↗
PubMed2005

Combining solid-phase microextraction and on-line preconcentration-capillary electrophoresis for sensitive analysis of pesticides in foods.

The combined use of solid-phase microextraction (SPME) and different on-line preconcentration strategies for ultrasensitive capillary electrophoresis-ultraviolet (CE-UV) analysis of five pesticides in a single run is investigated. Normal stacking mode (NSM), field-enhanced sample injection (FESI), and stacking with matrix removal (SWMR) are explored to increase the sensitivity of the CE-UV analysis of a selected group of pesticides (cyprodinil, cyromazine, pyrifenox, pirimicarb, and pyrimethanil). It could be observed that reverse polarity-stacking with matrix removal (RP-SWMR) provided the best results in terms of sensitivity (enhancement was up to 272-fold compared with normal injection). The separation buffer consisted of 0.4 mM cetyltrimethylammonium chloride (CTAC), 0.4 M acetic acid at pH 4 containing 5% v / v 2-propanol. This approach was then combined with SPME to determine the pesticides in water, apple, and orange juice. The combination of both preconcentration procedures allowed the determination of these pesticides at concentrations down to 2.5 microg / L in water and 3.1 microg / L in juices (i.e., levels well below the maximum residue limits allowed for these compounds). To our knowledge, this is the first report showing the great possibilities of the combined use of SPME, on-line sample preconcentration, and CE for pesticide analysis.

Carbamates↗
PubMedDate not supplied

Sensitivity analysis for evaluating nonlinear models of lung mechanics.

We present a combined theoretical and numerical procedure for sensitivity analyses of lung mechanics models that are nonlinear in both state variables and parameters. We apply the analyses to a recently proposed nonlinear lung model which incorporates a wide range of potential nonlinear identification conditions including nonlinear viscoelastic tissues, airway inhomogeneities via a parallel airway resistance distribution function, and a nonlinear block-structure paradigm. Additionally, we examine a system identification procedure which fits time- and frequency-domain data simultaneously. Model nonlinearities motivate sensitivity analyses involving numerical approximation of sensitivity coefficients. Examination of the normalized sensitivity coefficients provides direct insight on the relative importance of each model parameter, and hence the respective mechanism. More formal quantification of parameter uniqueness requires approximation of the paired and multidimensional parameter confidence regions. Combined with parameter estimation, we use the sensitivity analyses to justify tissue nonlinearities in modeling of lung mechanics for healthy and airway constricted conditions, and to justify both airway inhomogeneities and tissue nonlinearities during bronchoconstriction. The tools in this paper are general and can be applied to a wide class of nonlinear models.

Airway Resistance↗
PubMedDate not supplied

Uncertainty and sensitivity analysis of spatial predictions of heavy metals in wheat.

Heavy metals seriously threaten the health of human beings when they enter the food chain. Therefore, policymakers require precise predictions of heavy metal concentrations in agricultural crops. In this paper we quantify the uncertainty of regression predictions of Cd and Pb in wheat (Triticum aestivum L.) and the contributions to the uncertainties in these predictions associated with inputs to the regression model. For each node of the 500- x 500-m grid covering the arable soils in The Netherlands, a latin hypercube sample size of 1000 is constructed from the uncertainty distributions of the explanatory variables (pH, soil organic matter [SOM], and heavy metal concentration in soil), the regression coefficients, and the random term of the regression model. This sample is used as input for the regression model to obtain 1000 values from the uncertainty distributions of the log(Cd) and log(Pb) concentration in wheat. There were no nodes where the recent EU quality standards for Cd and Pb (0.2 mg kg(-1) fresh wt.) in wheat were almost certain to be exceeded. For most nodes with clay soils, the quality standard for Cd in wheat almost certainly will not be exceeded; for Pb this is much less certain. The uncertainty in the Cd concentration in soil contributes most to the uncertainty in the predicted Cd concentrations in wheat (36% on the average), followed by the random term of the regression model (23%). For Pb the contribution of the random term is by far the largest (52%).

Agriculture↗
PubMed1997

Sensitive analysis of [D-Pen2,5]enkephalin in rat serum by capillary electrophoresis and laser-induced fluorescence detection.

A highly sensitive analytical method based on capillary zone electrophoresis (CZE) coupled with a laser-induced fluorescence (LIF) detector was explored for the analysis of [D-Pen2,5]enkephalin (DPDPE) in rat serum. DPDPE and the internal standard Phe-Leu-Glu-Glu-Ile (P9396) were extracted from serum samples with C18 solid-phase extraction disk cartridges, followed by derivatization with tetramethylrhodamine-5-isothiocyanate (TRITC) isomer G before introduction onto the capillary column. Complete resolution of DPDPE and the internal standard from other serum components was achieved within 20 min on a 140 cm x 50 microns I.D. capillary column with borate buffer (25 mM. pH 8.3). With the current method, it is possible to detect 1.3E-18 mol of DPDPE on column. The results suggest that CZE-LIF is a promising method for the sensitive and specific quantitation of therapeutic peptides in biological matrices.

Animals↗
PubMed1990

Sensitive analysis of phospholipid molecular species by high-performance liquid chromatography using fluorescent naproxen derivatives of diacylglycerols.

A sensitive high-performance liquid chromatographic (HPLC) method for the separation and determination of diacylglycerophospholipid and diacylglycerol (DAG) molecular species has been developed. Phospholipids are hydrolysed with phospholipase C and the resulting DAGs are reacted with naproxen chloride in the presence of 4-dimethylaminopyridine. The naproxen-DAGs were purified by thin-layer chromatography on silica gel G plates. Molecular species were separated using reversed-phase HPLC with isocratic elution and determined by measuring the absorbance at 230 nm or fluorescence at 352 nm (excitation at 332 nm). The method was applied to the determination of diacylglycerophosphoethanolamine in rat cerebrum and cerebellum. The molar absorption coefficient of the naproxen derivatives was 53,000 lmol-1 cm-1 at 230 nm, permitting the generation of linear concentration-dependent determinations down to less than 10 pmol. A ten-fold increase in sensitivity was obtained with a fluorescence detection system owing to the fluorescent properties of the proposed adduct.

Animals↗
PubMed1999

ESI/ion trap/ion mobility/time-of-flight mass spectrometry for rapid and sensitive analysis of biomolecular mixtures.

An ion trap/ion mobility/time-of-flight mass spectrometry technique is shown to be a rapid and sensitive means of analyzing peptide/protein mixtures. In this approach, an ion trap is used to accumulate ions that have been electrosprayed from a mixture into concentrated packets. The ion packets are injected into a drift tube where components of the mixture are separated based on differences in mobility through a buffer gas. Ions that exit the drift tube are dispersed in a time-of-flight mass spectrometer for mass-to-charge (m/z) determination. The gas-phase separation strategy reduces congestion in the mass spectrum, and experimental mobilities complement m/z measurements in assigning peaks. Examples of the application of the approach to identification of peptides (from tryptic digests) and to separation of charge-state distributions from electrospray of a mixture containing ubiquitin and myoglobin are presented. Most peptides that are observed from tryptic digests of proteins such as cytochrome c and myoglobin can be identified from data that are acquired in under 1 min; studies of mixtures with known compositions indicate that detection limits are approximately 0.5-3 pmol for individual components. Factors that may influence the distributions that are observed, such as storage time in the trap, injection voltages used for the mobility experiment, and variations in ion cross section with charge state, are discussed.

Cytochrome c Group↗
PubMed1983

Mechanisms of suppression in the transfer of contact sensitivity. Analysis of an I-J+ molecule required for Ly2 suppressor cell activity.

The passive transfer of contact sensitivity (CS) by immune cells can be inhibited with an antigen-specific T suppressor factor. This factor is composed of two subfactors: an antigen-specific subfactor made by an Ly1+ cell (PC1-F) and a antigen nonspecific subfactor made by an Ly2+ T cell (TNBSA-F). The suppressive activity of the complete factor can be eliminated by depleting the assay population of Ly2+ cells, even though it is the Ly1+ cell in the population that transfers the adoptive immunity. This suggests that the Ly2+ cell in the assay population is needed to transduce the suppressive signal to the Ly1+ effector cell of DTH. We found that an Ly2+ cell from immune animals could be induced to produce a cell free subfactor that overcame the requirement for this Ttrans cell in the suppression of CS by TsF. The induction required only PC1-F, TNP-coupled spleen cells, and resulted in the production of an antigen-nonspecific I-J+ subfactor by immune Ly2+, I-J+ cells. The need for the Ly2+ transducer cell could also be overcome by addition of an I-J+ molecule secreted by Ly1 T cells hyperimmunized to SRBC. A suppressor complex made from mixing the I-J+ molecule with TNBSA-F could directly suppress the functional activity of immune T cells not only to transfer CS, but also to deliver help to B cells in an in vitro PFC response. This suppressive complex is antigen-nonspecific and does not require Ly2+ T cells in the assay population for suppressive activity. These results indicate that effector factors of the suppressor circuit require two molecules; one that contains the functional suppressor material and one that serves as a "schlepper," a molecule needed to deliver the suppression to the appropriate target cell. The ability to construct a functional suppressor complex from two subfactors raised against different antigens, using different immunization procedures, which were isolated from factors exhibiting different functional activities suggests that certain cells of the immune system may play a universal role in "transducing" the suppressive signal.

Animals↗
PubMed2004

Sensitivity analysis of causal inference in a clinical trial subject to crossover.

In many clinical trials it is possible for some subjects to cross over between treatment arms. One can evaluate the effect of crossover by modeling it as a missing-data problem, where for subjects who cross over, one treats the unobserved value of the outcome in the original randomization arm as the missing data. The as-treated analysis is invalid if the crossover is nonignorable, in the sense that the crossovers represent a nonrandom sample of the randomized subjects. A recent area of general interest is the development of methods for measuring the sensitivity of inferences to nonignorability in the missing-data mechanism; one such approach is that of Troxel et al. In this paper we apply their method to the problem of measuring sensitivity to nonignorable crossover in randomized trials, extending it to the case where the crossover mechanism may differ between arms. Our method allows us to identify circumstances under which the as-treated analysis may be more or less sensitive to nonignorable crossover. We illustrate it with the example of a randomized clinical trial (RCT) in multiple sclerosis and a study of the effect of military service on income.

Causality↗
PubMed2007

Sensitivity analysis of a nanowire-based surface plasmon resonance biosensor in the presence of surface roughness.

We have investigated the effect of surface roughness on the sensitivity of conventional and nanowire-based surface plasmon resonance (SPR) biosensors. The theoretical research was conducted using rigorous coupled-wave analysis with Gaussian surface profiles of gold films determined by atomic force microscopy. The results suggest that, when surface roughness ranges near 1 nm, the sensitivity of a conventional SPR system is not significantly affected regardless of the correlation length. For a nanowire-based SPR biosensor, however, we have found that the sensitivity degrades substantially with decreasing correlation length. In particular, at a correlation length smaller than 100 nm, a random rough surface may induce destructive coupling between excited localized surface plasmons, which can lead to prominent reduction of sensitivity enhancement.

Journal Article↗
PubMed2002

Simple and sensitive analysis of long-chain free fatty acids in milk by fluorogenic derivatization and high-performance liquid chromatography.

A highly sensitive high-performance liquid chromatography (HPLC) method is described for the simultaneous determination of some important saturated and unsaturated fatty acids in milk, including lauric (dodecanoic), myristic (tetradecanoic), palmitic (hexadecanoic), stearic (octadecanoic), palmitoleic (hexadecenoic), oleic (octadecenoic), and linoleic acids (octadecadienoic acids). The fatty acids were fluorogenically derivatized with 2-(2-naphthoxy)ethyl 2-(piperidino)ethanesulfonate (NOEPES) as their naphthoxyethyl derivatives. The resulting derivatives were separated by isocratic HPLC and monitored with a fluorometric detector (lambdaex = 235 nm, lambdaem = 350 nm). The fatty acids in milk were extracted with toluene, and the extract with the fatty acids was directly derivatized with NOEPES without solvent replacement. Determination of long-chain free fatty acids in milk is feasible by a standard addition method. A small amount of milk product, 10 microL, is sufficient for the analysis.

Animals↗
PubMed1992

High-sensitivity analysis of sialyl-oligosaccharide glycosylation sites in glycoproteins by miniaturized tryptic digestion and microcolumn liquid chromatography.

A highly sensitive analytical procedure was developed to assess the site of glycosylation in a model glycoprotein, bovine fetuin. First, sample cleavage with immobilized trypsin and the peptide map development are accomplished by microcolumn liquid chromatography. Second, the sialic acids content is measured fluorometrically using their precolumn conversion to quinoxaline derivatives. A unique preconcentration system was developed to secure sensitivity of the second measurement.

Amino Acid Sequence↗