Baseline changes in an isothermal titration microcalorimeter

Summary Isothermal titration microcalorimeters are submerged in an ambience at constant temperature and, this is the reason why there should not be variations in the baseline; but the experimental measures show that, in some cases, it is produced a jump in the baseline after the liquid injection. In this paper, it is studied the origin of this variation of the baseline in order to avoid it, if it is possible, or correct it and thus, to determine with the minimum error the amounts of energy or power developed in the energetic process that is being studied. The experimental results that are shown support the hypothesis that states that the cause of the baseline jump in an isothermal microcalorimeter is the variation of the thermal coupling between the content of the mixture cell and the axis of the stirrer, which is coupled, at the same time, with an area with a temperature slightly lower (in this case) than the thermostat temperature. This jump is independent from the dissipation and it always has the same sign. The magnitude of the baseline jump is variable and it mainly depends on the volume that the liquid content in a cell reaches and the placement of the stirrer within the cell, that can be changed in the handling process.     

Investigation of the effects of wall adsorption of the visualization agent on baseline noise characteristics for indirect UV detection in capillary electrophoresis

New insights into the effects of the wall adsorption of the visualization agent on baseline noise characteristics in indirect UV detection in capillary electrophoresis were provided. When compared to relatively small, hydrophilic cationic (1-(4-pyridyl)pyridinium chloride hydrochloride) or anionic chromophores (bromide and benzoate), the use of a UV-absorbing long-chain cationic surfactant (benzyldimethylhexadecylammonium chloride) as a probe (visualization agent) for studying baseline noise characteristics as a function of various experimental conditions, such as applied voltage, pH or buffer composition, was found to provide noise data that were very different under certain conditions. For cationic visualization agents that have a strong tendency of adsorbing onto the capillary surfaces due to electrostatic and/or hydrophobic interactions, it appeared that the interplay of both thermal as well as adsorption/desorption events occurring within the capillary is likely responsible for a fluctuation of the visualization agent concentration at the detector.     

Possibility of radioactivity measurement using an isothermal microcalorimeter

Journal of Radioanalytical and Nuclear Chemistry - Generally, short-lived medical isotopes and/or their generators are produced in nuclear reactors and cyclotrons. During the last decade, the...     

Effect of a stirring process in an isothermal titration microcalorimeter

In this paper, it is analysed the way in which the thermodynamic results obtained in an isothermal titration microcalorimeter, with continuous injection of a liquid and a variable mass are affected. Two aspects are presented, the first one refers to a variation in the baseline that takes place when the liquid mass is increased in the laboratory cell, this variation is due to the change in the thermal coupling between the stirrer and its contact with the thermostat. The second aspect is the analysis of the effect of the stirring process and the injection velocity on the homogenization of the remaining mixture in the laboratory cell.

The aim of the study of these two previous aspects is to increase the accuracy of the thermodynamic measures carried out. The variation of the baseline affects in a percentage from 1 to 2% of the total energy developed. It is also shown the necessity of a stirring process according to the injection velocity in order to obtain a homogeneous mixture at every instant. This fact allows to carry out a deconvolution of the calorimetric signal and to obtain directly the power developed in the mixture process in terms of the amount of mixed substance [Meas. Sci. Technol. 1 (1990) pp. 1285–1290; J. Thermal Analysis 41 (1994) pp. 1385–1392].     

Modellization of the mixture dissipation in a flow microcalorimeter

The signal processing of the experimental output produced by simultaneous injection of two liquids in a flow microcalorimeter allows, besides the determination of the mixture energy, to obtain information about the mixture thermokinetics. Starting from this information, a model of space-time behaviour of the mixture dissipation is proposed. The simulations carried out explain that an increase of the injection flow produces an increase in the dissipation length which could be located out of the detection zone.     

Changes in the Transfer Function of a flow microcalorimeter

Flow microcalorimeters are used to determine thermodynamic properties of liquid mixtures, the accuracy of these measures depends on the right calibration of the instrument. In this work the system is identified by means of the transfer functions of the two poles, it is proven that the first time constant and the sensitivity change with the value of rc _p f of the injected liquids (r - density, c _p - heat capacity, f - injection flow), and that the sensitivities obtained in the electrical and chemical calibrations are different for the same value of rc _p f because the dissipation in each case does not occur in the same place. As a summary of the calibration carried out, it is proposed a sensitivity value of 313±4 mV W^-1 for rc _p f<15 mW K^-1 that permits to make thermal measures with an uncertainty of 3%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Design and application of a liquid-flow adsorption micro calorimeter based on the Calvet-type DAK 1-1 microcalorimeter (USSR)

The construction and the properties of a liquid-flow adsorption microcalorimeter are described. The calorimeter is based on the commercially available Calvet-type DAK 1-1 microcalorimeter (USSR), which has been equipped with a flow system consisting of a pump, several sets of heat exchangers and an adsorption cell. The minimum detectable heat effect is 1W up to a flow rate of 30 cm³/h.Results on the application of the calorimeter to adsorption and desorption processes of nonionic (Triton X-100) and anionic (styrene phosphonic acid) surfactant solutions in water at an-Al₂O₃ surface are presented and discussed.

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Zusammenfassung Konstruktion und Eigenschaften eines Flüssigkeits-Strömungs-Adsorptions-Mikrokalorimeters werden beschrieben. Das Kalorimeter wurde weiterentwickelt aus dem Calvet-Mikrokalorimeter DAK 1-1 (USSR), das mit einem Strömungssystem aus einer Pumpe, verschiedenen Wärmeaustauschern und einer Adsorptionszelle ausgestattet wurde. Der kleinste nachweisbare Wärmeeffekt liegt bei 1W bis zu einer Durchflussgeschwindigkeit von 30 cm³ h^–1. Mit dem Kalorimeter erhaltene Messergebnisse zur Adsorption und Desorption wässeriger Lösungen von nichtionischen (Triton X-100) und anionischen (Styrenphosphonsäuren) Tensiden an-Al₂O₃ werden dargestellt und diskutiert.

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, 1-1 (), , , . 1 30 ³/. ( X–100) (- ) -l₂₃.

     

Adsorptive voltammetric procedure for the determination of platinum baseline levels in human body fluids

Summary An extremly sensitive procedure for the determination of platinum in human body fluids is presented. A high pressure decomposition of the samples is followed by adsorptive voltammetric measurement. A detection limit down to 0.2 ng Pt/l sample allowed baseline levels of platinum in body fluids (urine: 0.5–15 ng/l, blood and blood plasma: 0.8–6.9 ng/l) to be evaluated. The concentration ranges in body fluids of occupationally exposed people were determined to 21–2900 ng/l (urine), 32–180 ng/l (blood) and 95–280 ng/l (blood plasma).     

Equilibrium in an ideal adsorption layer during multiplet adsorption

The equilibrium in an ideal adsorption layer during adsorption of a mixture of substances whose molecules can occupy one or m elementary sites is examined. It is shown that the isotherm for any adsorbate in the mixture can be readily found if the isotherm is known for one of the adsorbed substances whose molecules occupy m elementary surface sites in the absence of other adsorbates. The form of the isotherm for multiplet adsorption depends on the distribution of the elementary sites on the surface.     

A titration microcalorimeter and the vesicle of mixed surfactants

A titration microcalorimeter with the sample cells of 1 mL and 3 mL volume was constructed by combining LKB-2107 ampule microcalorimeter with an improved Thermometric titration microcalorimeter. Its sensitivity and precision were tested with the baseline noise and stability, the measurement of energy equivalent, and the linear relation of electric energy and integral area as the function of voltage (V)-time (f). Its accuracy was demonstrated by measuring the dilution enthalpy of a concentrated sucrose solution and the micelle-forming enthalpy of sodium dodecyl sulfate (SDS) in aqueous solution respectively. At the same time, the enthalpy of interaction between SDS and didodecyldimethylammonium bromide (DDAB) was measured by using the titration microcalorimeter, and the phase behavior of SDS-DDAB aqueous mixture was discussed. The microcalorimetric results show that the enthalpy of interaction between SDS and DDAB micelles is -29.53 kJ/mol, the enthalpy of formation of 1:1 SDS-DDAB salt is -125.8 kJ/mol,     

Variation analysis of affinity-membrane model based on Freundlich adsorption

The variation analysis of membrane properties including membrane thickness and pore-size was carried out theoretically by using affinity-membrane model based upon the Freundlich adsorption equation. As the percentage variation of membrane thickness and distribution of pore-size increase, we find that (1) the time of total saturation is delayed; (2) the loading capacity at the point of breakthrough are decreased; (3) solute recovery efficiency and ligand utilization efficiency is decreased; (4) the thickness of unused membrane is increased. The results show that even small variations of thickness and distribution of pore size may severely degrade the membrane performance.     

A microcalorimeter for studying the magnetocaloric effect and the heat capacity in magnetic fields

The design of an automated microcalorimeter for determining the magnetocaloric effect and the heat capacity of suspensions and magnetic colloids in magnetic fields of from 0 to 1 T over a wide temperature range and the corresponding experimental procedure were described.     

Variation in surface energy heterogeneity of graphite due to adsorption of polyoxyethylene sorbitan monooleate

The heterogeneity of surface energy of graphite before and after adsorption of polyoxyethylene sorbitan monooleate (Tween80) was investigated by the nitrogen adsorption technique. The nitrogen adsorption energy distributions (AEDs) were calculated from the low-pressure isotherm data (i.e., the data of submonolayer adsorption) according to the regularization method. Based on the AED of pristine graphite, two types of dominant energetic surface are identified and assigned respectively to the basal surface and the irregular surface, including the stepped edges and defect sites. When the adsorption amount of Tween80 is raised, both the surface energy and the energy heterogeneity of graphite gradually decline. It is thus demonstrated that Tween80 prefers interacting with and screening higher energetic surfaces to lower ones.     

A new method of determining the thermal conductivities of energetic materials by microcalorimeter

A device of measuring the thermal conductivity of pellet of propellants and explosives has been constructed. A method and a calculation formula for determining the thermal conductivity of pellet of propellants and explosives under constant radial heat flow conditions by use of Joule effect is presented. Using this device and a microcalorimeter, type RD496-II, and two standard samples with known thermal conductivity, two instrument constant have been determined and the thermal conductivities of seven materials: plexiglass, teflon, DB propellant DB-2 (nitrocellulose(NC)/nitroglycerine(NG)/dinitrotoluene/dimethyl centralite/vaseline/PbO/CaCO₃, 59.6/25/8.8/3/1.2/1.2/1.2), DB propellant SQ(NC/NG/diethyl phthalate(DEP)/binder, 59/29/7/5), DB propellant RHN-149 (NC/NG/triacetin (TA)/binder-I, 52/25/8/15), DB propellant RHN-190 (NC/NG/TA/ binder-II, 52/26/7/15), 2, 4, 6-trinitrotoluene (TNT) at 298 K are measured. The results show that (1) the reproducibility of measurement for the heat (q) retained in investigated system after cutting the Joule current and the amount of heat flux through the wall of the investigated cylinder (Q _s) are less than 0.50% and within 0.10%, respectively; (2) the standard deviation of the thermal conductivity determined by using this method is less than 1.0%; (3) the values ofq, Q _s and internal radius of the cylinder are three principal factors affecting the magnitude of the thermal conductivity of these materials.     

Effect of the acid activation levels of montmorillonite clay on the cetyltrimethylammonium cations adsorption

For the first time, the intercalation properties of acid-activated montmorillonites treated at different acid/clay (w/w) ratios with a cationic surfactant cetyltrimethylammonium (C16TMA) hydroxide are reported. The acid activation causes a reduction in the number of cation exchange sides and, hence improves the exfoliation of the silicate sheets at higher pH values. The basal spacing increases significantly from 1.54 to 3.80 nm, and is related to the acid activation extent. The acid activated clays with acid/clay ratios above 0.2 intercalated significant amounts of C16TMA cations with a basal spacing of 3.8 nm compared to the non acid activated montmorillonite with a basal spacing of 2.10 nm. The 13C CP/MAS NMR indicates that the intercalated surfactants exhibit a significant degree of gauche conformation in the acid-activated clays. According to in-situ powder XRD, an increase of the basal spacing to 4.08 nm is observed at intermediate temperatures of 50-150 degrees C for organoclay with basal spacing of 3.80 nm, at higher temperatures above 300 degrees C, the decomposition of the surfactant occurs and the basal spacing decreases to a value of about 1.4 nm, with the persistence of a reflection at 3.8 nm for clay at a higher acid/clay ratio of 0.5.     

Effect of the injection velocity on the spatial localization of the mixture dissipation in a flow microcalorimeter

Summary The effect of the injection velocity in the chemical calibration of a flow microcalorimeter is studied in this article. The experimental measures show a parabolic variation of the sensitivity in terms of the injection flow. The considered hypothesis is that the maximum of the sensitivity curve is produced when the spatial area in which the mixture dissipation takes place is centred with regard to the detector system. When increasing the injection flow, this mixture zone moves till it goes out of the detection area making the sensitivity diminish. It has been defined a time constant _mix which is related to the establishment time of the homogeneous mixture and with the length occupied by the mixture dissipation. A study has been carried out with three liquid mixtures that have different behaviours; within these mixtures, _mix has been determined in terms of the injection flow and the considered hypothesis has been confirmed.     

Modellization of the spatial localization effect of the mixture dissipation on the sensitivity in a flow microcalorimeter

It is proposed a calorimetric model that helps to understand the dependence on the sensitivity of a flow microcalorimeter with the spatial localization of the energetic dissipation. The model allows to compare the spatial localization of different studied mixtures and permits us to conclude that in the ‘rapid’ mixtures, the length that the mixture dissipation occupies and the sensitivity remain nearly constant; however, in the mixtures called ‘slow’, the mixture length increases with the injection flow. This fact produces, at the same time, a clear variation of the sensitivity.     

Flicker noise spectroscopy in an analysis of the dynamics of atmospheric aerosol

Flicker noise spectroscopy was used to analyze measurements in the free atmosphere. The special features of correlations between the measured atmospheric aerosol parameters, namely, the total concentration of aerosol with particle size no larger than 3 nm, the concentration of particles whose size exceeded 150 nm, and the mean size of these particles, were determined and analyzed. These correlations could be used to create new models and reveal the rules governing the formation of new particles. Flicker noise spectroscopy was shown to offer much promise for atmospheric measurements.     

Hydrogen adsorption in an interpenetrated dynamic metal-organic framework

A metal-organic framework Zn(NDC)(4,4'-Bpe)(0.5).xG [NDC = 2,6-naphthalenedicarboxylate; 4,4'-Bpe = 4,4'-trans-bis(4-pyridyl)ethylene; G = guest molecules] has been synthesized, structurally characterized, and rationalized to be a two-interpenetrated elongated primitive cubic net. Powder X-ray diffraction and adsorption studies reveal the dynamic feature of the framework, which can take up hydrogen of about 2.0 wt % at 77 K and 40 bar and 0.3 wt % at 298 K and 65 bar.