Total Sample Concentration Research Articles

Pharmacokinetics of Esomeprazole in Critically Ill Patients.

BackgroundEsomeprazole, a potent proton pump inhibitor (PPI), is widely used for the prevention of stress ulcers in intensive care unit (ICU) patients.ObjectiveThis study investigates the pharmacokinetics (PK) of esomeprazole in critically ill patients.MethodsThe study included eligible adult ICU patients who received endotracheal intubation assisted mechanical ventilation for more than 48 h and had at least an extra risk factor for stress ulcers. All enrolled patients received once-daily intravenous (IV) esomeprazole 40 mg. After the first dose of esomeprazole was administrated, serial blood samples were collected at 3, 5, 15, 30 min and 1, 2, 4, 6, 8, and 10 h. The total sample concentrations of esomeprazole were measured by UPLC-MS/MS. Esomeprazole PK parameters were analyzed using noncompartmental analysis.ResultsA total of 30 patients were evaluable. Mean age and body mass index (BMI) were 61.97 years and 23.14. PK sampling on the first dose resulted in the following median (IQR) parameters: AUC0−∞ 8.06 (6.65–9.47) mg·h/L; MRT0−∞ 4.70 (3.89–5.51) h; t1/2 3.29 (2.7–3.87) h; V 24.89 (22.09–27.69) L; CL 6.13 (5.01–7.26) L/h; and Cmax 2.56 (2.30–2.82) mg/L.ConclusionsAccording to the label of esomeprazole, our study showed different esomeprazole PK parameters in ICU patients compared with healthy volunteers. Esomeprazole has unique pharmacokinetic parameters in critically ill patients.

Shape-Based Peak Identity Confirmation in Liquid Chromatography.

Chromatography is used to separate analytes in a mixture. In the absence of a detector providing analyte-specific information, the retention time is used to identify the analyte, typically by comparing the retention time of the unknown with that of a standard. This is the simplest of identification routines, but it remains the most widely used. The challenge is that analyte retention times can and do shift; sole reliance on retention time for identification is not prudent. Retention time is influenced by the total sample concentration, elution of components near the peak of interest, aging of a column, and so on, complicating time window-based identification. We propose a sameness threshold (ST) that is based on numerical comparison of shapes of chromatographic peaks for identification confirmation. We demonstrate shape-based identification confirmation or lack thereof of an unconfirmed peak by comparison with a shape library of standards. In numerous cases we look at, only one analyte in the shape library fits the putative identity. ST can be based on r2, the commonly used coefficient of determination used in regression analysis, or on an "index of width mismatch" that compares the widths of the peaks throughout the available height range.

Dynamic Nuclear Polarization with Vanadium(IV) Metal Centers

Summary Dynamic nuclear polarization (DNP) harnesses the large polarization of electron spins to dramatically increase nuclear magnetic resonance (NMR) sensitivity. This study expands the scope of DNP beyond its traditional focus on hyperpolarizing the solvent network using exogenous polarizing agents (PAs). We introduce 1H DNP with endogenous V4+ centers positioned in a set of vanadyl complexes with tunable V4+-1H distances. We traced the polarization transfer from V4+ to 1H spins, specifically differentiating between direct V4+-1Hs polarization transfer and the 1H spin-diffusion-mediated bulk solvent 1H polarization buildup and illuminated the effect of the V4+-1H distance on these processes. These results deepen our understanding of polarization pathways and expand the catalog of PAs to broad-line transition metals. This study establishes crucial first steps toward employing strategically positioned endogenous paramagnetic metal centers for DNP and the conceptual framework of hyperfine DNP spectroscopy that merges both spatial and chemical diagnosis of target nuclear spins.

Concentrations of pharmaceuticals and other micropollutants in groundwater downgradient from large on-site wastewater discharges.

Large subsurface treatment systems (LSTS) and rapid infiltration basins (RIB) are preferred onsite wastewater treatments compared to direct discharge of treated wastewater to streams and adjacent facilities. Discharge of these wastewater treatments may result in contaminant loading to aquifers that also serve as drinking water sources downgradient from the discharge site. Until recently, few studies have characterized the contribution of micropollutants (e.g. pharmaceuticals, fragrances, flame retardants, etc.) to receiving aquifers. We conducted a pilot project to characterize the occurrence of micropollutants in groundwater downgradient from 7 on-site treatment systems in Minnesota, USA: 5 community LSTS and 2 municipal RIB. One downgradient monitoring well was sampled three times at each facility over one year. Of 223 micropollutants analyzed, 35 were detected. Total sample concentrations ranged from 90 to 4,039 ng/L. Sulfamethoxazole (antibiotic) was detected in all samples at concentrations from 7 to 965 ng/L. Other pharmaceuticals (0.12–1,000 ng/L), organophosphorus flame retardants (10–500 ng/L), and other anthropogenic chemicals (4–775 ng/L) were also detected. The numbers and concentrations of micropollutants detected were inversely related to dissolved oxygen and depth to water. Ratios of pharmaceutical concentrations to human-health screening values were <0.10 for most samples. However, concentrations of carbamazepine and sulfamethoxazole exceeded screening values at two sites. Study results illustrate that large on-site wastewater systems designed to discharge to permeable soil or shallow groundwater effectively deliver pharmaceuticals and other micropollutants to groundwater aquifers and could contribute micropollutants to drinking water via water supply wells.

Organic contaminants in Great Lakes tributaries: Prevalence and potential aquatic toxicity

Organic compounds used in agriculture, industry, and households make their way into surface waters through runoff, leaking septic-conveyance systems, regulated and unregulated discharges, and combined sewer overflows, among other sources. Concentrations of these organic waste compounds (OWCs) in some Great Lakes tributaries indicate a high potential for adverse impacts on aquatic organisms. During 2010–13, 709 water samples were collected at 57 tributaries, together representing approximately 41% of the total inflow to the lakes. Samples were collected during runoff and low-flow conditions and analyzed for 69 OWCs, including herbicides, insecticides, polycyclic aromatic hydrocarbons, plasticizers, antioxidants, detergent metabolites, fire retardants, non-prescription human drugs, flavors/fragrances, and dyes. Urban-related land cover characteristics were the most important explanatory variables of concentrations of many OWCs. Compared to samples from nonurban watersheds (<15% urban land cover) samples from urban watersheds (>15% urban land cover) had nearly four times the number of detected compounds and four times the total sample concentration, on average. Concentration differences between runoff and low-flow conditions were not observed, but seasonal differences were observed in atrazine, metolachlor, DEET, and HHCB concentrations. Water quality benchmarks for individual OWCs were exceeded at 20 sites, and at 7 sites benchmarks were exceeded by a factor of 10 or more. The compounds with the most frequent water quality benchmark exceedances were the PAHs benzo[a]pyrene, pyrene, fluoranthene, and anthracene, the detergent metabolite 4-nonylphenol, and the herbicide atrazine. Computed estradiol equivalency quotients (EEQs) using only nonsteroidal endocrine-active compounds indicated medium to high risk of estrogenic effects (intersex or vitellogenin induction) at 10 sites. EEQs at 3 sites were comparable to values reported in effluent. This multifaceted study is the largest, most comprehensive assessment of the occurrence and potential effects of OWCs in the Great Lakes Basin to date.

Partitioning of fluoranthene between free and bound forms in stormwater runoff and other urban discharges using passive dosing

Partitioning of fluoranthene in stormwater runoff and other urban discharges was measured by a new analytical method based on passive dosing. Samples were collected at the inlet (n = 11) and outlet (n = 8) from a stormwater retention pond in Albertslund (Denmark), and for comparison samples were also obtained at a municipal wastewater treatment plant, a power plant, a contaminated site and a waste deposit in Copenhagen (n = 1 at each site). The freely dissolved concentration of 14C-fluoranthene in the samples was controlled by equilibrium partitioning from a pre-loaded polymer and the total sample concentration measured. The measurements yielded free fractions of fluoranthene in stormwater in the range 0.04–0.15 in the inlet during the first part of the runoff events increasing to 0.3–0.5 at the end of the events and in the outlet from the retention pond. The enhanced capacity of the different stormwater samples for carrying fluoranthene was 2–23 relative to pure water and decreasing during rain events. The enhanced capacity of stormwater showed a different relationship with suspended solid concentrations than the other types of urban discharges. Partitioning of fluoranthene to dissolved organic carbon was lower than partitioning to particulate organic carbon. Partitioning of fluoranthene to particulate organic matter in the 19 stormwater samples yielded a log KPOM of 5.18. The presented results can be used in stormwater quality modeling and assessment of efficiency of stormwater treatment systems. This work also shows the potential of the passive dosing method to obtain conversion factors between total concentrations, which are needed for comparison with water quality criteria, and freely dissolved concentrations, which are more related to toxicity and obtained by the use of most passive samplers.

A New Calibration Method for the Accurate Determination of Ethylene Content in Ethylene‐Propylene Copolymers by CRYSTEX‐IR

AbstractSummary: CRYSTEX is a fully automated instrument for the determination of Xylene Solubles in polypropylene and ethylene‐propylene copolymers, providing an excellent correlation with gravimetric methods. The instrument can be equipped with a dual band infrared (IR) detector to quantify the ethylene weight percentage (C2%) in the amorphous fraction, and in the whole polymer sample. In this work, a new approach based on multiple linear regression (MLR) models is presented, which makes use of two independent IR absorbance signals acquired simultaneously by the detector. A compromise model to predict directly C2% is proposed, which balances good accuracy and reduced experimental effort. MLR models able to predict the total sample concentration were also developed. The results were successfully validated using copolymer standards in a wide chemical composition range.

Dichlorvos concentrations in locally formulated pesticide (Ota-piapia) utilized in northeastern Nigeria.

Samples of locally formulated Ota-piapia utilized in northeastern Nigeria were investigated for concentration levels of dichlorvos aimed at specifying the preponderant active pesticide ingredient in the local formulation from this region. Gas chromatography-Flame Ionization detection (GC-FID) technique was used for the determination. Results indicated that all Ota-piapia samples studied showed presences of dichlorvos. The frequency distribution curve of concentration revealed 64% of total sample concentration cluster around the modal region of 7.7% w/v of dichlorvos. Though content uniformity was very poor with highest variability at mid concentration (5 - 10% w/v), but dichlorvos can safely be confirmed as the preponderant active pesticide ingredient in the local formulation ofOta-piapia from this region. The linearity of the method was good with determination coefficients of > 0.996 for target analyte. Therefore it is a matter of public health significance to regularly monitor pesticide residues in foods and humans in order to assess the food safety risk and population exposure to pesticides. The illegal formulation of Ota-piapia in this region by traders with little or no knowledge of public health policy must be checked through adequate control of the trade, use of pesticides and the enforcement of appropriate sanctions. Key words: Organophosphate, pesticide, local formulation, concentration levels, GC-FID.

Passive Dosing to Determine the Speciation of Hydrophobic Organic Chemicals in Aqueous Samples

A new analytical approach to determine the speciation of hydrophobic organic analytes is presented. The freely dissolved concentration in a sample is controlled by passive dosing from silicone (poly(dimethylsiloxane)), and the total sample concentration at equilibrium is measured. The free fraction is determined as the ratio between measured concentrations in pure water and sample. (14)C-labeled fluoranthene served as model analyte, and total sample concentrations were easily measured by liquid scintillation counting. The method was applied to surface water, stormwater runoff, and wastewater. In the untreated wastewater, 61% of the fluoranthene was bound to suspended solids, 28% was associated to dissolved organic matter, and 11% was freely dissolved, while in treated wastewater, the speciation was 16% bound to suspended solids, 4% bound to dissolved organic matter, and 80% freely dissolved. The free fraction in roof runoff (85%) and surface water (91%) was markedly higher than in runoff from paved areas, which ranged from 27 to 36%. A log K(DOC) value of 5.26 was determined for Aldrich humic acid, which agrees well with reported values obtained by fluorescence quenching and solid phase microextraction (SPME). This analytical approach combines simplicity with high precision, and it does not require any phase separation steps.

Potentiometric sensors for trace-level analysis

This review summarizes recent progress in the development and application of potentiometric sensors with limits of detection (LODs) in the range 10 −8–10 −11 M. These LODs relate to total sample concentrations and are defined according to a definition unique to potentiometric sensors. LODs calculated according to traditional protocols (three times the standard deviation of the noise) yield values that are two orders of magnitude lower. We are targeting this article at analytical chemists who are non-specialists in the development of such sensors so that this technology may be adopted by a growing number of research groups to solve real-world analytical problems. We discuss the unique response features of potentiometric sensors and compare them to other analytical techniques, emphasizing that the choice of the method must depend on the problem of interest. We discuss recent directions in sensor design and development and present a list of 23 sensors with low LODs, with references. We give recent examples where potentiometric sensors have been used to solve trace-level analytical problems, including the speciation of lead and copper ions in drinking water, the measurement of free copper in sea water, and the uptake of cadmium ions by plant roots as a function of their speciation.

Improved detection limits and sensitivities of potentiometric titrations.

Zero-current ion fluxes through polymer membranes of ion-selective electrodes (ISEs) may lead to biased endpoints of potentiometric titrations. The bias is eliminated, and the sensitivity of the end-point detection is improved through reducing transmembrane ion fluxes by an appropriate choice of the inner solution. Surprisingly, ISE membranes that have a significant primary ion flux toward the inner solution show much larger sensitivities than expected by titration theory; however, depending on the experimental conditions, their application may bias the endpoint. With the optimal systems, endpoint detection is now possible with total sample concentrations below 10(-6) M, as demonstrated by the titration of EDTA with a Pb2+ solution.

DETECTING AFLATOXIN IN SINGLE CORN KERNELS BY TRANSMITTANCE AND REFLECTANCE SPECTROSCOPY

Transmittance spectra (500 to 950 nm) and reflectance spectra (550 to 1700 nm) were analyzed to determine ifthey could be used to distinguish aflatoxin contamination in single whole corn kernels. Spectra were obtained on whole cornkernels exhibiting various levels of bright greenishyellow fluorescence. Afterwards, each kernel was analyzed for aflatoxinfollowing the USDAFGIS Aflatest affinity chromatography procedures. Spectra were analyzed using discriminant analysisand partial least squares regression. More than 95% of the kernels were correctly classified as containing either high(>100 ppb) or low (<10 ppb) levels of aflatoxin. Classification accuracy for kernels between 10 and 100 ppb was only about25%, but these kernels do not usually affect total sample concentrations and are not as important. Results were similar whenusing either transmittance or reflectance, and when using either discriminant analysis or partial least squares regression. Thetwofeature discriminant analysis of transmittance data gave the best results. However, for automated highspeed detectionand sorting, instrumentation that uses singlefeature reflectance spectra may be more practically implemented. Thistechnology should provide the corn industry with a valuable tool for rapidly detecting aflatoxin in corn.

Separation of particulate environmental samples by SPLITT fractionation using different operating modes

Procedures for gentle preseparation of particle suspensions prior to sedimentation field flow fractionation (SdFFF) analysis based on the use of Split-flow thin cell (SPLITT) fractionation (SF), were examined for isolating size fractions from both polydisperse standard silica samples and natural river particle samples. Two modes of SPLITT cell operation (conventional SF, full feed depletion SF (FFDSF)) are discussed and their performances compared. Recycling procedures for enhancing the resolution were tested and the degree of the separation attained was checked by optical microscopy and, in the case of the natural river particle samples, by coupling SdFFF with scanning electron microscopy (SEM) of the fractionated samples. The FFDSF has the advantage that no external dilution is introduced during the binary separation, so that the total sample concentration is unaffected and the separation obtained appears to be equally good for the two methods.

A Study of Calcium and Magnesium Migration Patterns of Soft Fruits Canned in a Variety of Syrups

The distribution of calcium and magnesium between the solid and liquid fractions of canned soft fruits was studied. The mineral migration patterns, migration rates and equilibrium levels were compared for different syrup packs and fruits. Atomic absorption values for calcium and magnesium were converted to ratios of mineral in the fruit compared to total sample concentration and expressed as percentages. The majority of mineral transfer from fruit to syrup occurred rapidly during processing and the hours following. Fruit mineral percentages decreased only about 5% from 24h post process to 6mo later. The different syrups had significantly different effects on mineral migration patterns and rates but did not significantly affect the final equilibrated values (P<0.01). Final values varied significantly for the different fruits and in all cases significantly more magnesium than calcium was released from the fruit into the syrup (P<0.01). Between 35 and 50% of the calcium and magnesium had leached into the syrup by the time the product would theoretically be consumed, representing a significant loss of available nutrients if the syrup is not consumed with the fruit.

A general method for quantitative spectrochemical analysis with the d.c. arc performed with solid samples in briquetted form

A general method for quantitative spectrochemical analysis is presented. In this method the powdered sample is mixed with a great excess of buffer material and pressed into a briquette. The briquette is placed in the cup of the sample electrode and arced with a direct current of 10 Amp. The buffer is composed of 12% LiF and 88% graphite by weight. The total sample concentrations used in the briquettes are 1% 0.1%, 0.01%, so principal and trace elements can be analysed. The minimum amount of sample needed 0is 1.5 mg. The method can be used for a great diversity of sample materials. Results are presented for a number of BCS and NBS standard samples.