Determination of lead in seawater by inductively coupled plasma optical emission spectrometry after separation and pre-concentration with cocrystallized naphthalene alizarin

An analytical method for separation and pre-concentration of lead in seawater for determination by inductively coupled plasma optical emission spectrometry has been investigated. Lead was retained in the solid phase (0.5 g) composed of co-precipitated naphthalene and alizarin red. The solid phase quantitatively sorbs Pb(II) at pH 8–9, and the metal was eluted using 5.0 ml of 2 mol l⁻¹ nitric acid. The effect of NaCl, KCl, BaCl₂, CaCl₂, Na₂SO₄, MgCl₂ and Na₃PO₄ on the sorption of Pb(II) in the solid phase was studied. A set of solutions containing varying amounts of electrolytes (0.5; 1.0; 3.0 and 5.0% m/v) with Pb (50 μg) was prepared and the recommended procedure applied. The Na₃PO₄ was found to interfere; the other electrolytes did not interfere up to 5% m/v. A pre-concentration factor of 40 was obtained in this analytical procedure. The limit of detection and limit of quantification for Pb(II) were 53 and 176 μg l⁻¹, respectively. Lead was determined in seawater samples collected in Salvador city, Bahia, Brazil. The precision, expressed as R.S.D., was 1.8–4.6%, and the recovery of lead added to seawater samples was 95–97%.     

Dicholorbenzyl alkyl ether homologs as retention index markers and internal standards for the analysis of environmental samples using capillary gas chromatography

A homologous series of 2,4-dichlorobenzyl alkyl ethers (DCBEs) have been synthesized and purified for use as retention index calibrants and internal standards. They are stable, sensitive to ECD and FID and ideal for GC-MS, with base peaks at m/z 159/161. The retention index calibration against the n-alkanes for a linear temperature program (LTP) series is given and recommendations made for the most suitable members of the DCBE series for use as internal standards in organochlorine (OC) residue analysis.     

Medium effects on fluorescence quantum yields and lifetimes for coumarin laser dyes

Fluorescence quantum yields and lifetimes of coumarin dyes are sharply reduced in polar solvents if amine substituent groups are free to rotate. The polar solvent effect is interpreted in terms of relaxation of excited dye from an initial planar conformation to a twisted zwitterionic state.     

A Large Volume Injection Procedure for GC-MS Determination of PAHs and PCBs

A simple on-column injection system for large volume of liquid samples for the GC-MS determination of traces of PAHs and PCBs has been investigated. A deactivated fused silica capillary 20 m × 0.53 mm I.D. and 2 meters of an HP5 column (0.53 mm,1 m film thickness) were used as retention gaps. Injection volumes of 80 L for PAHs and 90 L for PCBs, allow determination of 5–50 ng L^–1 PAHs and 11–44 ng L^–1 PCBs in hexane solution with an RSD of < 10%. The method has been used for the determination of PCBs and PAHs in soil sample.     

Compehensive two-dimensional gas chromatography (GC×GC) and its applicability to the characterization of complex (petrochemical) mixtures

In general, petrochemical products contain only a limited number of chemical classes of compounds (sample dimensionality). The enormous number of individual components within these classes, however, soon puts limitations upon a single chromatographic technique when it comes to adequate characterization of these products. Comprehensive two-dimensional gas chromatography (GC×GC) clearly opens the possibility of estimating the composition of hydrocarbon mixtures in a far more detailed fashion than hitherto possible. Although the emphasis of papers of GCxGC thus far almost exclusively applies to the unsurpassed peak-capacity, in the oil industry there is a need for characterization, rather than for analyzing all the individual compounds. In principle a GCxGC system can provide an almost perfect match between its intrinsic properties and the dimensionality of oil samples. To establish the applicability of GCxGC towards petrochemical analytical challenges, a commercially aavailable prototype instrument was subjected to an exhaustive characterization of a typical hydrocarbon precess stream and a fast characterization of a light gas oil. Although there are no fundamental limitations towards the quantitative aspects of a GCxGC system, this paper confines itself to qualitative results only. Quantitative aspects of GCxGC will be published in a forthcoming paper.     

Determination of gold in geological samples by x-ray fluorescence spectrometry after extraction with tributyl phosphate

The behaviour of gold and elements impeding its x-ray fluorescence spectrometric (XRF) determination, namely zinc, lead and arsenic, was studied during their extraction from hydrochloric acid, nitric acid, and aqua regia solutions using tributyl phosphate as a solid extractant [SE(TBP)]. Extraction of gold from pulps after aqua regia leaching was found to be the most favourable approach for the quantitative and selective recovery of gold. The gold distribution ratio, D_Au, is ca. 10⁴ ml g^?1. For extraction from hydrochloric acid solutions the D_Au value also exceeds 10⁴ in the whole range of gold concentrations studied (10^?8?10^?4 M), but it decreases substantially with increasing extraction temperature, from 5 × 10⁵ ml g^?1 at 20°C to 9 × 10³ ml g^?1 at 70°C. An anomalously high distribution ratio of lead, D_Pb ≈ 10³ ml g^?1, was observed during extraction from hydrochloric solutions in the presence of chlorine. This could be explained by the formation of the chloro complexes of lead(IV). An XRF method for the determination of gold in natural samples was developed, which includes back-extraction of gold from SE(TBP) using a hot 0.025 M thiourea solution, providing a thin sample layer for secondary XRF. For 25 g of sample material the limit of determination is 10 ng g^?1 (10^?6%). The accuracy of the technique was checked using different reference materials. The results agreed within 10%.     

Use of non-aqueous capillary electrophoresis for the quality control of commercial saffron samples

A non-aqueous capillary electrophoresis (NACE) method for quantifying the seven crocin metabolites that are the major biologically active ingredients of saffron was developed. Separation is done by using a fused silica capillary filled with a 12.5 mM H3BO3/37.5 mM sodium tetraborate methanolic solution as background electrolyte. The results obtained were compared with the total index "safranal value", widely used as a quality measure of saffron products. The comparison revealed that the proposed NACE method provides useful information not obtained in the safranal value. Infact, samples with a similar safranal value can contain crocin metabolites in different concentrations and relative proportions. This new method is very useful for quality control in commercial saffron samples.     

Separation of L-DOPA and four metabolites in plasma using a porous graphitic carbon column in capillary liquid chromatography

Summary A sensitive HPLC method with marbofloxacin (MAR) as internal standard and fluorescence detection is described for the analysis of ofloxacin (OFL) enantiomers in plasma samples. Plasma samples were prepared by adding phosphate buffer (pH 7.4, 0.1m), then extracted with trichloromethane.S-OFL,R-OFL, and the internal standard were separated on a reversed-phase column with water-methanol, 85.5∶14.5, as mobile phase. The concentrations ofS-OFL andR-OFL eluting from the column (retention times 7.5 and 8.7 min, respectively) were monitored by fluorescence detection withλ _ex = 331 andλ _em = 488 nm. The detection and quantitation limits were 10 and 20 ng mL⁻¹, respectively, forS-OFL and 11 and 21 ng mL⁻¹ forR-OFL. Response was linearly related to concentration in the range 10 to 2500 ng mL⁻¹. Recovery was close to 93% for both compounds. The method was applied to determination of the enantiomers of OFL in plasma samples collected during pharmacokinetic studies.     

以学生为中心的物理化学远程教学初探

During the fight against the new coronavirus epidemic, the "Physical Chemistry" team of Beijing Normal University used various network platforms and tools, such as MOOC of China University, Rain Classroom and WeChat Group in the teaching process. The exploration and practice of online learning of "Physical Chemistry" is carried out based on MOOC teaching, with student learning as the center and teacher guidance as the support. Taking the most difficult chapter of "fundamentals for statistical thermodynamic" as an example, we designed a complex teaching program that includes previews, watching MOOC videos in class, real-time online exercises, teachers' answers, and after-class reflection and questioning. The students were encouraged to learn independently through the reserved information, designed activities and assignments. Practice shows that the online course has cultivated the students' self-management ability, trained their critical thinking skills, and achieved good teaching results.     

氯磺化聚乙烯的γ—辐射交联

氯磺化聚乙烯(简称CSM)由于存在SO_2Cl基团很容易通过金属氧化物进行化学交联,但至今未见其辐射交联的详细报道.本文探讨氯含量对CSM辐射交联的影响. 所用CSM系吉林化工公司产品:20型(含氯量29～33％,下同),40型(33～37％)和30型(40～45％).将CSM和防老D按一定比例混炼均匀,再在140℃左右热压成形.试样用3.33×10~(15)Bg ~(60)Co于室温限量空气下进行辐照.辐照过的试样于80℃处理2小时以消除俘陷自由基.在氮气保护下先后用二甲苯和无水乙醇,加热回流48小时和8小时,测定凝胶含量.