Seawater—A test of multicomponent electrolyte solution theories. II. Enthalpy of mixing and dilution of the major sea salts

In a continuing effort to predict the physicochemical properties of seawater from the properties of single aqueous electrolyte solutions, the pairwise heats of mixing at constant molal ionic strength,I=1.0 ional, have been determined for the six possible pairs of salts from the set (NaCl, Na₂SO₄, MgCl₂, MgSO₄) at 30°C. In addition, heats of dilution for two aqueous solutions formed from these salts and havingI=1.0 ional have been determined at 30°C. In order to present the most thermodynamically consistent results, it was found necessary to apply a correction term to the relative apparent equivalent enthalpies given in the literature at 30°C. These correction terms derived from a consideration of published results on heats of dilution at very low concentrations. Further, in order to make predictions for seawater at 25°C, it was deemed desirable to refit existing heat-capacity data. The heats relative apparent equivalent enthalpies for the two mixtures mentioned as well as for seawater. The estimates are based on the theoretical equation of Reilly and Wood for charge-asymmetric mixtures which derives from the work of Friedman. In the most applicable cases, the estimates agree with experimental relative apparent equivalent enthalpies to within 5%. In general, the results substantiate the theoretical equation.Taken in part from the Ph.D. dissertation of W. H. Leung, University of Miami, Miami, Florida 33149.     

流动注射区域采样法测定镀锌钝化液中高浓度锌

本文建立了流动注射二甲酚橙光度法测定镀锌纯化液中Ｚｎ￣２＋的自动分析方法。利用区域采样技术和调整管路参数自动完成对样品的上千倍稀释，确定了最佳分析条件并研究了干扰离子的影响及消除办法。所建方法仪器简单，分析速度为８４次／小时，变异系数（Ｚｎ￣２＋１６．０ｇ／Ｌ，ｎ＝２０）为１．Ｏ％，用于实际钝化液分析，相对误差小于±１０％。     

Determination of 19-norandrosterone in CCQM-P68. NIST results using an isotope dilution liquid chromatography/tandem mass spectrometry method

The US National Institute of Standards and Technology (NIST) participated in an international interlaboratory study under the auspices of the Consultative Committee for Amount of Substance (CCQM) for the determination of 19-norandrosterone (19-NA) in urine, the principal metabolite of nandrolone and certain other synthetic testosterone substitutes banned for use by the World Antidoping Agency (WADA). Prior to this study, NIST developed a candidate reference measurement procedure based upon isotope dilution liquid chromatography/tandem mass spectrometry. This method was applied to a urine sample distributed to the participants in the study by the Australian National Measurement Institute, Pymble, Australia (NMIA). The NIST results were in very good agreement with those from the other participants, all of whom used methods based upon gas chromatography/mass spectrometry. All known significant sources of uncertainty were evaluated, resulting in a relative expanded uncertainty of less than 5% (coverage factor k = 2).     

The thermodynamics of mixing C6 and C7 compounds with a bicyclic compound at infinite dilution

The activity coefficients at infinite dilution have been measured at 25°C for cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, benzene, n-hexane, 1-hexene, 1-hexyne, n-heptane, 1-heptene and 1-heptyne in decahydronaphthalene, bicyclohexyl, 1,2,3,4-tetrahydronaphthalene and cyclohexylbenzene. These results, together with previously determined H _m ^E and V _m ^E have been used to calculate the partial molar excess thermodynamic properties of mixing at infinite dilution.     

Application of the Prigogine-Flory-Patterson theory part III. Mixtures of a bicyclic compound,benzene, cyclohexane,n-hexane with a cycloalkane,cyclohexene, a cycloalkadiene and benzene

The Prigogine-Flory-Patterson theory of liquid mixtures has been qpplied to the H _m ^E and V _m ^E for binary mixtures of a bicyclic compound, benzene, cyclohexane and n-hexane with a cycloalkane, cyclohexene, a cycloalkadiene and benzene. Furthermore the Prigogine-Flory theory has been used to predict activity coefficients at infinite dilution from the experimentally determined H _m ^E at 25°C for the mixtures cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene and benzene with a bicyclic compound. The predictions are compared to experimental results.     

Cyclic esters of aliphatic diacids with pyrocatechol and hydroquinone

Cyclic esters of adipic acid, suberic acid and sebacic acid were prepared by reaction of the acid dichlorides and pyrocatechol or hydroquinone in benzene under high dilution conditions. While only the cyclic dimers could be obtained from hydroquinone, pyrocatechol formed cyclic monomers as well as cyclic dimers (and also a cyclic dimer with succinic acid). The structure of all compounds was confirmed by¹H-NMR- and mass spectra. The crystal structures of the pyrocatechol esters were determined by single crystal X-ray analysis.

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Cyclische Ester aliphatischer Dicarbonsäuren mit Brenzcatechin und Hydrochinon

Zusammenfassung Es wurden cyclische Ester von Adipinsäure, Korksäure und Sebacinsäure durch Reaktion der entsprechenden Säure-Dichloride mit Brenzcatechin oder Hydrochinon bei hoher Verdünnung hergestellt. Während mit Hydrochinon lediglich die cyclischen Dimeren erhalten werden konnten, wurden mit Brenzcatechin sowohl cyclische Monomere als auch cyclische Dimere erhalten (ebenfalls das cyclische Dimer mit Bernsteinsäure). Die Strukturen wurden mittels¹H-NMR und Massenspektren gesichert. Die Kristallstrukturen der Brenzcatechin-Ester wurden mittels Röntgenstrukturanalyse bestimmt.

     

Isotope dilution determination of polycyclic aromatic hydrocarbons in olive pomace oil by gas chromatography-mass spectrometry

A gas chromatographic (GC) method with mass spectrometry detection (MS) for the determination of eight polycyclic aromatic hydrocarbons (PAHs) in olive pomace oil has been developed. The oil was diluted with n-pentane and extracted by liquid-liquid partition with dimethyl sulphoxide (DMSO). After water addition and back-extraction with cyclohexane, a thin-layer chromatography on silica gel was performed as a further purification step. The PAHs spot was scraped off from the plate and the final extract was concentrated and analysed by GC-MS in full scan mode. The eight PAHs under investigation were determined in the presence of the corresponding labelled compounds added as internal standards to the sample at the beginning of the analytical process. The identified PAHs were then quantified by the isotope dilution methodology assuring the compensation of the concentration of each analyte for any variation in the sample preparation. The method precision was satisfactory with relative standard deviation (R.S.D.) values in the range 3.6-12.7% for all PAHs. The average recovery rates ranged from 69.0 to 97.5%. Accuracy was also calculated for benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene and benzo[ghi]perylene by analysing a certified reference material (CRM 458, coconut oil) with adequate results. All response curves exhibited a linear fit from 0.1 to 10 microg ml(-1) and the determination coefficients R2 were better than 0.9942. The limits of detection (0.1-0.4 microg kg(-1)) were acceptable when compared with the maximum permitted limit of 2 microg kg(-1) for each of the eight considered PAHs and 5 microg kg(-1) for the sum of the eight PAHs established by the Italian legislation. Measurement uncertainty was finally calculated identifying and quantifying the uncertainty components of the analytical process. The relative expanded uncertainties (Uc), expressed as percent values were in the range 8.5-11.4% thus appropriate for residues quantification in the range of concentrations considered in the present study.     

Rigorous bounds on the storage capacity of the dilute Hopfield model

We study a neural network model consisting ofN neurons where a dendritic connection between each pair of neurons exists with probabilityp and is absent with probability 1-p. For the Hopfield Hamiltonian on such a network, we prove that ifp c[(lnN)/N]^1/2, the model can store at leastm= _cpN patterns, where _c 0.027 ifc 3 and decreases proportional to 1/(–lnc) forc small. This generalizes the results of Newman for the standard Hopfield model.     

Determination of uranium in marine sediment pore waters by isotope dilution inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) was used in an isotope dilution mode to assay small-volume (0.25 ml) sediment pore waters for their uranium contents, using ²³⁶U as the spike. The only pretreatment required was a simple dilution by a factor of 20, which gave sufficient volume for three replicate analyses per sample. Rapid and accurate results were obtained for a variety of samples and standards, ranging in concentration from 0.05 to 10 ng U ml^?1. A suite of 30 samples can be analysed in less than 6 h by this method. The relative standard deviation was better than 1.9%, with a detection limit, based on 3σ background, of 2 pg U ml^?1 in solution (40 pg ml^?1 in samples). Sea water is a difficult matrix for ICP-MS and thus the method is generally suitable for uranium determinations in many other sample solutions.     

Development of a stable isotope dilution UPLC‐MS/MS method for quantification of dexmedetomidine in a small amount of human plasma

Dexmedetomidine (Dex) is a selective central α2‐agonist with anesthetic properties and has been used in clinical practice for sedation in the intensive care unit (ICU) after operations. In this study, an analytical assay for the determination of Dex in a small amount of plasma was developed for the application to pediatric ICU trials. The quantification of Dex was constructed using the original stable isotope Dex‐d₃ for electrospray ionization‐tandem mass spectrometry (ESI‐MS/MS) in the selected reaction monitoring mode. A rapid ultra‐performance liquid chromatography technique was adopted using ESI‐MS/MS with a runtime of 3 min. Efficacious concentration levels (50 pg/mL to 5 ng/mL) could be evaluated using a very small amount of plasma (10 μL) from patients. The lower limit of the quantification was 5 pg/mL in the plasma (100 µL). For sample preparation, a solid‐phase extraction was used along with the OASIS‐HLB cartridge type. Recovery values ranged from 98.8 to 100.3% for the intra‐ [relative standard deviation (RSD), 0.9–1.3%] and inter‐ (RSD, 0.9–1.5%) day assays. A stable test had recovery values that ranged from 97.8 to 99.7% with an RSD of 1.0–1.9% for the process/wet extract, bench‐top, freeze–thaw and long‐term tests. This method was used to measure the Dex levels in plasma from pediatric ICU patients. In the clinical ICU trial, the small amount of blood (approximate plasma volume, 200 μL) remaining from blood gas analysis was reused and targeted for the clinical analysis of Dex in plasma. Copyright © 2013 John Wiley & Sons, Ltd.