Evaluation of indoor exposition to benzene, toluene, ethylbenzene, xylene, and styrene by passive sampling with a solid-phase microextraction device

A solid-phase microextraction (SPME) sampling method is developed to evaluate indoor exposure to benzene, toluene, ethylbenzene, xylene, and styrene with gas chromatography and flame ionization detection for quantitative analysis. An SPME holder with a 100-pm polydimethylsiloxane (PDMS) and 65-pm PDMS-divinylbenzene fiber coating is tested in different air relative humidity conditions. The method gives good resolution, shows a linear response, is repeatable, and presents high sensitivity. This method is compared with National Institute of Occupational Safety and Health (NIOSH) active sampling.     

Determination of phenyltoloxamine salicylamide, caffeine, paracetamol, codeine and phenacetin by HPLC

A reversed-phase high-performance liquid chromatographic method for the determination of six common analgesics (phenyltoloxamine dihydrogen citrate, salicylamide, caffeine, paracetamol, codeine phosphate and phenacetin) is presented. The method is specific for detection and determination of each of these compounds in a complex mixture, without pretreatment. A 10-mum C(18) silica gel stationary phase is used with a methanol-acetonitrile-water-tetrahydrofuran mixture (20:20:55:5 v/v) and spectrophotometric detection at 254 nm. All six components are eluted within 7 min. The method has given good results for three commercial products containing two, three and five active ingredients respectively. Phenacetin, a common analgesic which might be found in other formulations, is used as an internal standard.     

Eine mikromethode der flammen-atomabsorptions- und emissionsspektrometrie (platinschlaufen-methode)—II: Die bestimmung von As,Bi, Cd,Hg, Pb,Sb, Se,Te, Tl,Zn/Li,Na, K,Cs, Sr,Ba

This paper described the continuation of the work of Part I dealing with a microanalytical method in which the sample is introduced into a flame using an electrically heated platinum loop. This device is used in connection with an atomic absorption (AA) spectrometer. The detection limits are one to two orders of magnitude better than those of conventional flame AAS. The reproducibility depends on the element and is in general 3–5% (relative standard deviation) for concentrations in the $\text{ng}\text{ml}$ range. The platinum loop method can be also applied for flame emission analysis of small amounts of sample or the determination of low concentrations (alkalis). This application gives access to determinations in the lower ng or the pg range (detection limit of lithium: 0.6 pg).     

Reduced multireference coupled-cluster method: barrier heights for heavy atom transfer, nucleophilic substitution, association, and unimolecular reactions

The recently developed reduced multireference coupled-cluster method with singles and doubles (RMR CCSD) that is perturtatively corrected for triples [RMR CCSD(T)] is employed to compute the forward and reverse barrier heights for 19 non-hydrogen-transfer reactions. The method represents an extension of the conventional single-reference (SR) CCSD(T) method to multireference situations. The results are compared with a benchmark database, which is essentially based on the SR CCSD(T) results. With the exception of seven cases, the RMR CCSD(T) results are almost identical with those based on SR CCSD(T), implying the abatement of MR effects at the SD(T) level relative to the SD level. Using the differences between the RMR CCSD(T) and CCSD(T) barrier heights as a measure of MR effects, modified values for barrier heights of studied reactions are given.     

Crude fat, diethyl ether extraction, in feed, cereal grain, and forage (Randall/Soxtec/submersion method): collaborative study

A method for determining crude fat in animal feed, cereal grain, and forage (plant tissue) was collaboratively studied. Crude fat was extracted from the animal feed, cereal grain, or forage material with diethyl ether by the Randall method, also called the Soxtec method or the submersion method. The proposed submersion method considerably decreases the extraction time required to complete a batch of samples. The increase in throughput is very desirable in the quest for faster turnaround times and the greater efficiency in the use of labor. In addition, this method provides for reclamation of the solvent as a step of the method. The submersion method for fat extraction was previously studied for meat and meat products and was accepted as AOAC Official Method 991.36. Fourteen blind samples were sent to 12 collaborators in the United States, Sweden, Canada, and Germany. The within-laboratory relative standard deviation (repeatability) ranged from 1.09 to 9.26% for crude fat. Among-laboratory (including within) relative standard deviation (reproducibility) ranged from 1.0 to 21.0%. The method is recommended for Official First Action.     

Crude fat, hexanes extraction, in feed, cereal grain, and forage (Randall/Soxtec/submersion method): collaborative study

A method for determining crude fat in animal feed, cereal grain, and forage (plant tissue) was collaboratively studied. Crude fat was extracted from the animal feed, cereal grain, or forage material with hexanes by the Randall method, also called the Soxtec method or the submersion method. The use of hexanes provides for an alternative to diethyl ether for fat extractions. The proposed submersion method considerably decreases the extraction time required to complete a batch of samples compared to Soxhlet. The increase in throughput is very desirable in the quest for faster turnaround times and the greater efficiency in the use of labor. In addition, this method provides for reclamation of the solvent as a step of the method. The submersion method for fat extraction was previously studied for meat and meat products and was accepted as AOAC Official Method 991.36. Fourteen blind samples were sent to 14 collaborators in the United States, Sweden, Canada, and Germany. The within-laboratory relative standard deviation (repeatability) ranged from 1.23 to 5.80% for crude fat. Among-laboratory (including within) relative standard deviation (reproducibility) ranged from 1.88 to 14.1%. The method is recommended for Official First Action.     

Determination of B, Si, Cr, Mo, Th and Hf in UF(6) by end-on viewed ICP-AES

A spectrographic analysis method is described for the determination of B, Si, Cr, Mo, Th and Hf in UF(6) Uranium is separated from UO(2)F(2) using a TBP [tributyl phosphate] extraction-elution resin column technique. The six impurity elements, including B and Si, in the fluorine-containing extraction-elution solution are determined by end-on viewed ICP-AES. The method is simple, rapid and suitable for routine analysis.     

Lingos, finite state machines, and fast similarity searching

We apply a recently published method of text-based molecular similarity searching (LINGO) to standard data sets for the purpose of quantifying the accuracy of the approach. Our implementation is based on a pattern-matching finite state machine (FSM) which results in fast search times. The accuracy of LINGO is demonstrated to be comparable to that of a path-based fingerprint and offers a simple yet effective method for similarity searching.     

Rapid potentiometric method for the analysis of mica,talc, feldspar,nepheline syenite,and clay

A simple rapid and reliable potentiometric method is given for the analysis of a group of Egyptian ores having the similarity of being insoluble silicates which contain more or less the same metallic components but with different ratios, by application of the method of back titration of unconsumed EDTA in hexamine-buffered media using Hg(II) and Bi(III) as titrants and silver amalgam as indicator electrode.     

A general NMR method for rapid, efficient, and reliable biochemical screening

High-throughput screening is usually the method of drug-lead discovery. It is now well accepted that, for a functional assay, quality is more important than quantity. The ligand-based or protein-based NMR screening methodologies for detecting compounds binding to the macromolecular target of interest are now well established. A novel and sensitive NMR method for rapid, efficient, and reliable biochemical screening is presented. The method named 3-FABS (three fluorine atoms for biochemical screening) requires the labeling of the substrate with a CF(3) moiety and utilizes (19)F NMR spectroscopy for the detection of the starting and enzymatically modified substrates. The method allows for high-quality screening of large compound or natural product extract collections and for measuring their IC(50) values. Applications of this technique to the screening of inhibitors of the Ser/Thr kinase AKT1 and the protease trypsin are presented. In addition, an interesting application of 3-FABS to functional genomics is also presented.     

Computation of dynamic adsorption with adaptive integral,finite difference,and finite element methods

Analysis of diffusion-controlled adsorption and surface tension in one-dimensional planar coordinates with a finite diffusion length and a nonlinear isotherm, such as the Langmuir or Frumkin isotherm, requires numerical solution of the governing equations. This paper presents three numerical methods for solving this problem. First, the often-used integral (I) method with the trapezoidal rule approximation is improved by implementing a technique for error estimation and choosing time-step sizes adaptively. Next, an improved finite difference (FD) method and a new finite element (FE) method are developed. Both methods incorporate (a). an algorithm for generating spatially stretched grids and (b). a predictor-corrector method with adaptive time integration. The analytical solution of the problem for a linear dynamic isotherm (Henry isotherm) is used to validate the numerical solutions. Solutions for the Langmuir and Frumkin isotherms obtained using the I, FD, and FE methods are compared with regard to accuracy and efficiency. The results show that to attain the same accuracy, the FE method is the most efficient of the three methods used.     

Simultaneous HPLC determination of caffeine, theobromine, and theophylline in food, drinks, and herbal products

A rapid and selective high-performance liquid chromatographic (HPLC) method is developed for the separation and determination of caffeine, theobromine, and theophylline. The chromatography is performed on a Zorbax Eclipse XDB-C8 column (4.6 x 150 mm i.d., 5-microm particle size) at 25 degrees C, with a mobile phase of water-THF (0.1% THF in water, pH 8)-acetonitrile (90:10, v/v). The flow rate is 0.8 mL/min, and detection is by UV at 273 nm. This method permits the simultaneous determination of caffeine, theobromine, and theophylline in food, drinks, and herbal products with detection limits of 0.07-0.2 mg/L and recoveries of 100.20-100.42%. Correlation coefficients, for the calibration curves in the linear range of 0.2-100 mg/L, are greater than 0.9999 for all compounds. The within- and between-day precision is determined for both retention times and peak area. The data suggests that the proposed HPLC method can be used for routine quality control of food, drinks, and herbal products.     

Simultaneous microdetermination of carbon,hydrogen, mercury,chlorine, bromine and sulphur in organic compounds

A simple, reliable method for the simultaneous microdetermination of carbon, hydrogen, mercury, chlorine (or bromine) and sulphur in organic compounds is described. The intermediate storage technique is used. Sulphur and the halogens are absorbed on electrolytic silver and determined gravimetrically or titrimetrically. Mercury is absorbed on gold wire, and is weighed as the metal or desorbed and determined by a mercury-8-hydroxy-quinoline method.     

卡尔曼滤波分光光度法用于钴、镍、铜、锌、镉的同时测定—5-Br-PADAP-CPB法

本文运用卡尔曼滤波(KF)递推算法,以2-(5-溴-吡啶偶氮)-5-二乙氨基苯酚(5-Br-PADAP),溴化十六烷基吡啶(CPB)同时测定了五组分混合物:Co、Ni、Cu、Zn和Cd中各元素百分含量,合成样分析结果良好。用模型数据可测百分含量相差50倍的离子混合物。     

Visible spectrophotometric determination of tantalum in soil, sediment, minerals, and alloys

A new, sensitive, and selective method is described for the spectrophotometric determination of Ta(V). The method is based on the extraction of the Ta(V)-F-CV+ complex (CV+ = crystal violet cation) with a benzene solution of imidoyl derivatives (ID), i.e., N,N'-diphenylbenzamidine (DPBA), N-hydroxy-N,N'-diphenylbenzamidine, and N-(2,5-dimethyl)phenyl-p-tolylimidoylphenylhydrazine, from sulfuric acid solution; DPBA was selected for detailed study. The molar absorptivities of the Ta(V)-F-CV+-ID complexes in the benzene solution were in the range of (1.00-1.65) x 10(5) L/mol x cm at 600 nm. The limit of detection was 7 ng Ta/mL (which had an absorbance greater than that of the blank + 3 standard deviations). The optimization of the analytical variables, the composition of the complex, and the effect of diverse ions in the determination of Ta are discussed. The present method was applied to the determination of Ta in environmental samples, i.e., soil, sediment, minerals, and alloys.     

Determination of Cr,Fe, Co,Ni, Cu,Zn, As and Pb in liquid chemical waste by energy dispersive X-ray fluorescence

A method for simultaneous determination of Cr, Fe, Co, Ni, Cu, Zn, As e Pb in liquid chemical waste using Energy Dispersive X-Ray Fluorescence (EDXRF) technique was evaluated. A small sample amount (200 μL) was dried on a 6.35 μm thickness Mylar film at 60 °C and the analyses were carried out using an EDXRF spectrometer operated with an X-ray Mo tube (Zr filter) at 30 kV/20 mA. The acquisition time was 300 s and the Ga element was utilized as internal standard at 25 mg/L for quantitative analysis. The method trueness was assessed by spiking and the detection limit for those elements ranged from 0.39 to 1.7 mg/L. This method is notable because it assists the choice of the more appropriated waste treatment procedure, in which inter elemental interference is a matter of importance. In addition, this inexpensive method allows a non-destructive determination of the elements from ₁₉K to ₉₂U simultaneously.     

KCl-NaCl(1:1mol)-RECl3熔体的电导率(RE=La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu、Y、Ce族、Y族)

用交流电桥法测定了熔融KCl-NaCl(1:1摩尔)-RECl₃的电导。比电导的温度函数表达式如下: κ=A+B(t-700) κ:比电导(Ω^-1·cm^-1);t:温度(700—850℃); A、B:本文给出的常数。讨沦了实验值与计算值的偏差,当稀土氯化物在熔体中的浓度为10—50重量百分数时可能形成了络合物。     

Preparation,infrared and Raman spectra,force field and thermodynamic functions for Trifluoromethylsulfenyl Bromide,CF3SBr

Trifluoromethylsulfenyl bromide was obtained by a new preparative method. Its IR (vapour and pure solid) and Raman (liquid) spectra are fully characterized and an assignment is proposed for the observed bands. A normal coordinate analysis was made by means of a stewise-coupling method. Thermodynamic properties in the temperatur range between 200—1000 K are tabulated.     

Quantitative symmetry and chirality--a fast computational algorithm for large structures: proteins, macromolecules, nanotubes, and unit cells

Symmetry is one of the most fundamental properties of nature and is used to understand and investigate physical properties. Classically, symmetry is treated as a binary qualitative property, although other physical properties are quantitative. Using the continuous symmetry measure (CSM) methodology one can quantify symmetry and correlate it quantitatively to physical, chemical, and biological properties. The exact analytical procedures for calculating the CSM are computationally expensive and the calculation time grows rapidly as the structure contains more atoms. In this article, we present a new method for calculating the CSM and the related continuous chirality measure (CCM) for large systems. The new method is much faster than the full analytical procedures and it reduces the calculation time dependency from N! to N(2), where N is the number of atoms in the structure. We evaluate the cost of the applied approximations, estimate the error of the method, and show that deviations from the analytical solutions are within an error of 2%, and in many cases even less. The method is applicable at the moment for the cyclic symmetry point groups- C(i), C(s), C(n), and S(n), and therefore it can be used also for chirality measures, which are the minimal of the S(n) measures. We demonstrate the application of the method for large structures across chemistry: proteins, macromolecules, nanotubes, and large unit cells of crystals.