Sample Concentration Changes Research Articles

Simulation Research on Blood Detection Sensing with Parity-Time Symmetry Structure

To realize the design of a medical sensor with excellent comprehensive performance indexes, herein, a plasma concentration sensing model satisfying the Parity-Time (PT) symmetric condition is proposed. In this paper, the transfer matrix method was used to simulate the transmittance spectrum of the structure, according to the amplification effect on defect mode transmission and various detection performance indexes of the structure. We numerically optimized the parameters of the structure, such as the number of PT-symmetry unit cell N, the sample layer thickness dD as well as the macroscopic Lorentz oscillation intensity α in the PT-symmetry unit cell. The calculation results demonstrate that when the sample concentration changes from 0 g/L to 50 g/L, the wavelength of defect peak shifts from 1538 nm to 1561 nm, and the average quality factor, sensitivity, average figure of merit, average detection limit and average resolution of the structure can reach 78,564, 0.4409 nm/(g/L) (or 227.05 nm/RIU), 11,515 RIU−1, 5.1 × 10−6 RIU and 0.038 g/L, respectively. Not only the sensitivity and resolution of the PT-symmetry structure are better than that of the similar sensors, but it also has excellent comprehensive detection performance, which indicates that the developed sensor can be used in high-precision biomedical detection devices.

Rapid quantitative determination of blood propofol concentration throughout perioperative period by negative photoionization ion mobility spectrometer with solvent-assisted neutral desorption

Rapid and quantitative determination of blood propofol concentration is important for anesthesiologists to accurately control intraoperative propofol dose, timely monitor physiological statuses of patients and greatly improve the safety of surgery. Herein, a dopant-assisted negative photoionization ion mobility spectrometer with the optimized ionization region structure and the three-way inlet design was developed, increasing the generation ratio of the reactant ions O2−, and improving the ionization efficiency of propofol molecules. Besides, the addition of methanol-anisole solution during injection promoted the neutral desorption of propofol in blood, further improving the detection sensitivity by an order of magnitude, eliminating any sample pretreatment and effectively reducing the single analysis time to less than 1 min compared to the previous article. The dual calibration quantitative method, i.e. the method of calibrating the O2− concentration and the sample concentration changes during the entire process of detecting propofol through the integral value of M·O2− and the maximum signal intensity of O2−, successfully achieved accurate quantification of blood propofol. And the linear calibration curve of propofol was obtained with the range of 0.1–15 ng μL−1 and with the limit of detection of 0.03 ng μL−1, which was fulfilled to conduct propofol determination throughout the perioperative period. Finally, this method was applied to clinically measure the blood propofol concentration in patients newly regained consciousness with concentrations ranging from 0.2 ng μL−1 to 3 ng μL−1, and it turned out that the older patient had the lower propofol concentration in blood.

Electrical Tweezer for Droplet Transportation, Extraction, Merging and DNA Analysis.

Droplets of aqueous solutions distributed in an immiscible oil phase are increasingly used and investigated as a means to handle and assay small volumes of samples. The primary attraction of this method is that surface interactions are kept to a minimum, and changes in sample concentration, especially due to adsorption to the walls, are avoided. Microfluidic methods to generate, transport, merge, split and perform reactions in droplets were developed recently. These methods depend on the continuous flow of the two phases involved inside closed microfluidic channels. Alternatively, an electrowetting phenomenon was also exploited to control the movement of droplets between two solid substrates. However, there are some situations where small volume sample transport and assaying are required in open systems. Here, we demonstrate a simple electromechanical probe (tweezers) that is capable of manipulating a small aqueous droplet in a bi-layer oil phase. The tweezer consists of two needles positioned close to each other and uses polarization of the aqueous droplet in an applied electrical field to confine the droplet between the needles with minimal solid contact. Mechanical motion of the tweezer can be used to transport the droplet to various positions. Operations such as aliquoting, merging and transport are demonstrated. Finally, this method was used to perform a DNA amplification assay where droplets of the sample and the amplification mixture are aliquoted separately, mixed and amplified using an in-situ heater. This electromechanical tweezer is of interest in low-throughput, small-volume biological and chemical assays where the investigator requires direct and open access to the samples.

Coulometric calcium pump for thin layer sample titrations.

A selective electrochemical calcium pump based on a fast diffusive calcium ionophore-based membrane is reported. An initially nonpolarized ionophore-based membrane allows one to establish a net calcium flux by applying a potential step function (i.e., 250 mV for 30 s). The resulting calcium flux is released into a microliter scale thin layer reservoir, and the resulting ion perturbation is monitored by either a potentiometric or a coulometric readout. This chemical perturbation in the thin layer thus acts as a titration agent that is precisely controlled by coulometry. A linear correlation between released and detected calcium is confirmed by the two different readout modes. Having demonstrated the efficiency of the calcium pump in background electrolyte solutions, a complexometric titration with known concentrations of EDTA in the thin layer sample was performed. With the potentiometric readout, titrations in the range of 0.25-0.75 mM gave a precision of 3%, whereas the coulometric readout gave a range of 0.02-0.12 mM and a precision of 2%. Improved precision is expected by better control of the thin layer geometry by microfabrication. The significance of this work is that the coupling of a selective calcium pump with a thin layer element can give rise to rapid and complete sample concentration changes and result in a promising platform for titrations either on the laboratory bench or for in situ measurements in environmental or diagnostic settings.

13C NMR spectroscopy for determining the acylglycerol positional composition of lampante olive oils. Chemical shift assignments and their dependence on sample concentration

Two Lampante olive oils with free acidity expressed as oleic acid of 25.9 and 8.4 g per 100 g were used to carry out the 13C NMR study for the assignment of all resonances of free fatty acid fraction and of the acylglycerol fraction comprising 1(3)-mono- (1(3)-MAG), 1,3-di- (1,3-DAG), 1,2-di- (1,2-DAG) and triacylglycerols (TAG). The glycerol carbon resonances were found to be resolved according to the esterification degree of the glycerol molecule but no data were available on the length and the unsaturation pattern of the acyl chains. It was the spectral region where the C-1 carboxy carbons resonate that enabled the determination of free fatty acids and of different acylglycerol species. Moreover, within each acylglycerol class, the acyl chain distribution between the 1,3- and 2- glycerol positions was also calculated where the saturated, vaccenate, oleate and linoleate chains were detected as baseline resolved resonances in 1(3)-MAG, 1,3-DAG, 1,2-DAG and TAG. The variability of chemical shifts to sample concentration changes was also evidenced in all the frequency ranges being studied where the methylene C-2 and C-3 carbons underwent the most dramatic changes in their resonance patterns which prevented any resonance assignment.

No delayed temporal response to sample concentration changes during enhanced microdialysis sampling using cyclodextrins and antibody-immobilized microspheres

The temporal response to concentration changes external to a microdialysis probe containing trapping agents in the perfusion fluid was studied. Native beta-cyclodextrin and a water-soluble beta-cyclodextrin polymer were used as trapping agents in the microdialysis perfusion fluid to study the temporal concentration response to carbamazepine, a hydrophobic analyte. The temporal response of microdialysis probes containing antibody-immobilized microspheres against five different cytokines (tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), interleukin-2 (IL-2), IL-4, and IL-5) to concentration changes outside of the probe was also determined. In both cases, no delayed temporal response of enhanced microdialysis was observed for either carbamazepine or the cytokines as compared to standard microdialysis sampling procedures.

On-line monitoring of trihalomethanes in drinking water using continuous-flow purge and cryofocusing gas chromatography–mass spectrometry

A continuous-flow purge-and-trap–GC–MS system was developed for on-line monitoring of THMs (trihalomethanes) in drinking water. Three systems with different traps and purging flow-rates are discussed. In order to minimize interference from water vapor, total purge gas volume and injection temperature were controlled during analysis. Shorter sample concentration time and GC separation time reduced total cycle time to less than 5 min. The detection limits of the system could be lowered to 10 ppt, 25 ppt, 40 ppt, and 50 ppt (w/w) for CHCl 3, CHCl 2Br, CHClBr 2, and CHBr 3, respectively. This system could detect changes in sample concentration when applied to the on-line monitoring of THMs in drinking water.

Osmotic dehydration progression in apple tissue II: generalized equations for concentration prediction

In Part I of the present communication, osmotic dehydration experiments at atmospheric pressure were carried out using apple ( Granny Smith var.) slices (20 and 30 mm thick) at 20°C, 30°C, 40°C and 50°C. The slices were subjected to treatment for varying periods of time (0.5, 1, 2, 3, 6, 12, 22 and 34 h) by using a sucrose solution (65% (w/w) as osmotic agent following which, slices, 1.5 mm thick, were obtained to determine water and sugar contents throughout the sample thickness. In an attempt to understand the osmotic phenomena, an approach based on the “advancing disturbance front” (ADF) concept was developed. In this second part, generalized equations developed from the concept of ADF have been proposed to describe the kinetics of sample concentration changes either in terms of concentration profiles or average concentrations.

Determination of correlation times from selective and non-selective spin-lattice relaxation rates and their use in drug-drug and drug-albumin interaction studies

The effects of the changes in sample concentration on the NMR chemical shifts and on the selective and non-selective spin-lattice relaxation rates (R1S and R1NS) of the three isomers of nitrobenzaldeyde guanyl hydrazone (NBGH) pure and with bovine serum albumin (BSA) were measured in solution. The results were used to determine the correlation times (tc), showing that the degree of intermolecular drug-drug association varies with the nitro group position on the ring and that this degree of association interferes with the interaction of these drugs with BSA. The results suggest that the degree of drug-drug and drug-BSA association are related to the in vitro anti-Trypanosoma cruzi activity of these compounds.

Excitation-emission-matrix fluorescence spectroscopy applied to humic acid bands in coral reefs

Abstract An investigation of the three-dimensional excitation-emission-matrix (EEM) fluorescence spectra of humic acids and other organic matter from corals and other sources is reported, the results of which have implications for the use of corals as paleoenvironmental indicators. Four characteristic excitation/emission peaks were identified in the samples studied, at 310 430 , 340 450 , 390 490 and 280 (320–350) nm, the last of these attributed to protein fluorescence. The positions of these peaks were essentially invariant between different samples, including coral extracts, solid corals, seawater, and commercially-available humic acids, although their relative intensities showed considerable variation. The use of the EEM technique in the present work has demonstrated that changes in sample concentration can considerably change the intensity distribution of the fluorescence spectra, particularly if strongly absorbant, non-fluorescent species are present. Comparison of the EEM spectra of organic matter extracted from bright and dull coral bands showed the spectroscopic structure of the fluorescence emitted to be essentially identical for both bands; the emissions appear to differ only in their absolute intensities.

An automatic sampling device for capillary zone electrophoresis

AbstractAn automatic sampling device has been developed for capillary zone electrophoresis. The sample is introduced to the column electrokinetically by rapidly exchanging buffer for sample in a narrow channel drilled in a plexiglass block. The autosampler is capable, under computer control, of performing multiple sample injections from a large volume sample source (such as a reaction vessel) as the sample concentration changes, and thus presents the possibility of analyzing time‐varying processes by CZE. Peak area reproducibility in electropherograms obtained after use of the sampler is less than 1% and efficiency is more than 2.2 × 105 theoretical plates.

Thermal lens technique for sensitive kinetic determinations of fast chemical reactions. Part I. Theory

The thermal lens effect can be successfully explained by use of the presently available theories. However, the existing theories fail for cases where the sample concentration changes with time, i.e., when the sample undergoes a chemical reaction. The objective of this work is to demonstrate that the thermal lens technique can be used for the sensitive kinetic determination of fast chemical reactions. It is systematically approached from two different directions: the theoretical aspect which is described in this paper and the experimental section which will be reported in the following paper. Specifically, novel theories which are based on the parabolic as well as the aberrant model have been derived to describe the thermal lens signal for cases where the sample concentration changes with time. Based on the developed theories, computer calculations were then performed to simulate conditions for various chemical reactions. It was found that in all cases, both of the developed (parabolic and aberrant based) theories can be used successfully to determine not only the order of the reaction but also the reaction rate constant.