Voltammetric method for direct determination of nickel in natural waters in the presence of surfactants

Voltammetric procedures for direct Ni(II) determination in natural water samples are described. The procedures are based on nickel deposition to the metallic state and then its oxidation in the presence of dimethylglyoxime with the formation of the complex adsorbed on the electrode. Reduction of the complex is exploited in the detection step. Due to the application of a sufficiently negative deposition potential the interference from surfactants is minimized. The detection limits for Ni(II) are 2x10(-9) and 2x10(-10) mol l(-1) for deposition times of 30 and 120 s, respectively. The influence of foreign ions is also presented.     

A simple and very sensitive spectrophotometric method for the direct determination of copper ions

A sensitive spectrophotometric method for the direct determination of copper in aqueous samples without a preconcentration step has been developed. It is based on the formation of a yellow complex with the chromogenic reagent di-2-pyridyl ketone benzoylhydrazone (dPKBH) in an alkaline medium. The complex stoichiometry was 1:2 (Cu:dPKBH) and presents maximum absorbance at 370 nm. The influence of chemical variables affecting the behaviour of the system such as pH, concentration of dPKBH, buffer solution and ethanol, order of addition of the reagents and stability of the complex, were evaluated. The molar absorptivity (epsilon) was 3.92x10(4) L mol(-1) cm(-1), and Beer's law was obeyed up to 3 mg L(-1) of copper. The relative standard deviation was 0.46% (n=11) for a sample containing 1 mg L(-1) Cu(II). The limit of detection was 2.5 micro g L(-1) and was therefore more sensitive than the direct methods reported previously. Finally, the method was successfully validated by analysing several real samples with different matrices, such as tap water, natural water or copper alloys, with an average relative error of 2.46%.     

FTIR-ATR spectroscopic determination of the distribution of surfactants in latex films

FTIR-ATR (Fourier Transform Infra-Red-Attenuated Total Reflection) has been used to analyze the surface composition of coalesced acrylic latex films. The behavior of two anionic surfactants has been characterized. It has been found that surfactant distribution depends on the nature of the surfactant. A comparison between the normalized absorbance in transmission and in reflection has shown an enrichment of surfactants at the surfaces of films with a coalescence time of 3 days. The surfactant concentration at the film-air interface is higher than at the film substrate interface. A concentration gradient exists through the film thickness. In addition, the incompatible surfactant migrates towards the interface as coalescence proceeds.     

A radiometric method for the determination of non-ionic surfactants

A radiometric method for the determination of non-ionic surfactants of ethylene oxide type has been elaborated. The principle of the method is the formation of an associate¹³³Ba-non-ionic surfactant — dicarbolide and its extraction into a mixture nitrobenzene-chloroform /41/. The extracted activity of¹³³Ba is proportional to the non-ionic surfactant concentration in the sample. The factors influencing the determination of non-ionic surfactants in the real waste solution after washing have been studied. The possibility of the determination of non-ionic surfactants by the calibration graph method and by the method of standard addition was verified.     

Development of a rapid and sensitive method for determination of cysteine/cystine ratio in chemically defined media

Two rapid, sensitive and quantitative methods for the determination of the cysteine and cystine ratio in complex defined media feedstock using monolithic reversed-phase liquid chromatography (RPLC) and RPLC–MS are presented. Cysteine is pre-derivatised with purified 2-chloro-1-methylquinolinium tetrafluoroborate (CMQT) and separated from other derivatisation products on a narrow-bore 50 mm × 2 mm I.D. monolithic C₁₈ column with UV detection at 355 nm. For reversed-phase LC (RPLC) the separation is carried out isocratically using a mobile phase of 50 mM trichloroacetic acid (TCA) adjusted to pH 2.5 with lithium hydroxide (LiOH) and acetonitrile (83:14) pumped at 1.5 mL/min with an elevated column temperature. For RPLC–MS an ammonium acetate and acetonitrile gradient method was developed with a reduced flow rate of 0.3 mL/min. The treatment of the samples consisted of dividing them into two aliquots, the first aliquot is analysed for cysteine and the second aliquot is analysed for cystine after its quantitative reduction to cysteine using tris(2-carboxyethyl)phosphine (TCEP). Both methods are linear, with R² > 0.999 for 0.25–500 μM for cysteine and 0.25–250 μM for cystine using the LC–UV method, sensitive, with detection limit of 36 nM for cysteine, and precise, with ≤1.1% RSD for both retention time and peak area (n = 6). Samples (n = 31) of an industry standard and supplied chemically defined media feedstock were analysed, finding cysteine ranging from 1.56 to 2.26 μg/mL and cystine from 1062.02 to 1348.13 μg/mL.     

A sensitive method for the determination of tritium in urine

An analytical procedure was developed for the determination of tritium in urine. The content of contaminants in urine after treatment is reduced markedly so that no influence is expected on tritium measurements by a liquid scintillation counter. The established analytical procedure was successfully applied for urine from the general public in Japan.     

A spectroscopic investigation of aggregations in chlorophyll solutions

Abstract— Absorption and emission spectra are reported for polar and non-polar solutions of chlorophyll a and chlorophyll b. These spectra can be interpreted in terms of the formation of chlorophyll dimers and more highly aggregated forms. The phosphorescence spectra of polar and non-polar solutions of chlorophyll a are identical and are associated with emission from a π-π-* triplet state.     

An atomic absorption spectrometric method for the determination of non-ionic surfactants

A method is described for the determination of non-ionic surfactants in the concentration range 0.05–2 mg l^-1.Surfactant molecules are extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozincate(II) and the determination is completed by atomic absorption spectrometry. With a 150-ml water sample, the limit of detection is 0.03 mg l^-1(as Triton X-100).The method requires a single phase separation step, is applicable, without modification, to fresh, estuarine and sea-water samples and is relatively free from interference by anionic surfactants; the presence of up to 5 mg l^-1 of anionic surfactant (as LAS) introduces an error of no more than 0.07 mg l^-1 (as Triton X-100) in the apparent non-ionic surfactant concentration.     

An extraction—spectrophotometmc method for the determination of non-ionic surfactants

The surfactant is extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozincate(II), and zinc(II) in the extract is determined spectrophotometrically after addition of l-(2-pyridylazo)-2-naphthol and triethanolamine. With a 150-ml water sample, the limit of detection is 15 μg l^-1 (as Triton X-100). The method requires only one extraction and is applicable, without modification, to fresh, estuarine and sea-water samples.     

Photochemical determination of the solubility of oxygen in various media

A photochemical method for determining the oxygen concentration in air-saturated non-aqueous solvents has been developed. Solutions containing a sensitizer (Rose Bengal or Methylene Blue) and 1,3-diphenylisobenzofuran (DPIBF) as an oxygen acceptor are irradiated at 546 or 633 nm and the absorbance at 404 nm is monitored. The dissolved oxygen content is found from the change in absorbance and the known 1:1 stoichiometry of addition of singlet oxygen to DPIBF. The solubilities found, accurate to +/- 6%, for oxygen in air-equilibrated solvents, are (mM): acetone, 2.37; acetonitrile, 2.42; dimethylsulfoxide, 0.33; ethanol, 1.94; N-methylformamide, 1.31. Measurements on mixed acetone-N-methylformamide solvents showed that the solubility of oxygen does not vary with solvent composition in a predictable manner.     

A sensitive spectrophotometric method for the determination of desloratadine in tablets

A simple, rapid, and sensitive visible spectrophotometric method was developed, for the first time, for analysis of desloratadine (DE) in tablets. The method is based on the deep-blue colored TCNQ*- radical anion formed by interaction of the drug (n-donor) with 7,7,8,8-tetracyanoquinodimethane (TCNQ, pi-acceptor) in acetonitrile at ambient temperature. Optimum conditions for the reaction were investigated, absorbances were read at 843 nm, and the linearity range for concentrations of DE was found to be 1.5-13 microg/mL. The reaction product remains stable up to 8 h when kept at room temperature in the dark. The developed method was validated and successfully applied to the determination of DE in tablets. The tablets were also analyzed with a column liquid chromatography method reported in literature. The results from both methods were statistically compared by t- and F-tests. No significant difference was found for the means and standard deviations at 95% confidence level. Accuracy was examined through recovery studies. Being very simple and reliable, the method can be recommended for routine quality control analysis of DE in tablets.     

A sensitive method for the determination of nitroamines in alcoholic beverages

Summary Nitrosamines in alcoholic beverages and malted barley were analysed by adsorption from the gas phase onto a porous polymer trap of Chromosorb 104 and subsequent desorption of the trapped compounds directly to a gas chromatograph fitted with glass capillary column and alkali-FID. The detection limit for NDMA was 0.05 g/l in beer samples and 0.3 g/kg in malted barley.Presented at the 14th International Symposium on Chromatography London, September, 1982     

HPAE-PAD – a sensitive method for the determination of carbohydrates

High performance anion exchange chromatography with pulsed amperometric detection (HPAE-PAD) was used for the determination of eleven monosaccharides. Three analytical columns with different selectivities were tested, and the resulting separations were compared calculating precision and detection limits. The monosaccharides could be separated on CarboPAC PA10 in one analysis run with the lowest detection limits and a high precision. For the determination of polysaccharides and humic bound carbohydrates in natural organic matter, an hydrolysis step had to be carried out. With the exception of fructose, the recoveries varied between 56% and 83%. The described methods were applied for the determination of bound carbohydrates in a bog lake water and a soil extract without preconcentrating the samples.     

铟的灵敏光度测定法

我国对微量铟的显色反应研究得较少.最常用的是碱性染料萃取光度法,但操作冗繁而且苯的毒性较大.因此寻找灵敏度高而又能在水相测定铟的新方法是很有必要的. 用苯荧光酮(2,3,7-三羟基-9-苯基-6-荧光酮,PF)作显色剂的胶束增溶分光光度法已应用于锗、钼、锡、镓等的测定,但用类似的方法测铟则尚未见报道.我们的实验证明,在pH为7.7～8.9的醋酸-氢氧化铵缓冲介质中,铟与PF及氯化十六烷基吡啶(OPC)生成玫瑰红色的三元配合物,其配合比为In(III):PF:CPC=1:2:2,表观稳定常数为8.6×10~(10),摩尔吸收系数达1.28×10~5.提出用乙酸乙酯萃取分离杂质.利用本显色反应测定微量铟,方法灵敏且稳定,准确度和精密度均较好.     

A sensitive method for the ultraviolet spectrophotometric determination of chloride

A new method for the determination of chloride ion is based on the formation of phenylmercury(II) chloride, its extraction into chloroform and reaction with sodium diethyldithiocarbamate to form phenylmercury(II) diethyldithiocarbamate. This complex has spectral maxima at 257 and 297 nm. either of which can he used for quantitative purposes. The molar absorptivities are 21.3·10³ and 6.5·10³ respectively. referred to the chloride ion. The method is especially suitable for the determination of trace amounts of chloride in aqueous solution and has been applied to samples of drinking water. Amounts of chloride in the range 0.04 0.32 p.p.m. can be determined in 250-ml aqueous samples with an average relative mean error of 12%. The method can be used also for bromide and iodide, and for organomercury(11) compounds. Interferences are minimal and the method compares favourably with the standard mercury(II) thiocyanate procedure.     

Near-infrared spectroscopic observation of the ageing process in archaeological wood using a deuterium exchange method

The ageing degradation of the fine wood structure of dry-exposed archaeological wood was investigated by Fourier transform near-infrared spectroscopy with the aid of a deuterium exchange method. The archaeological wood sample was taken from an old wooden temple in Japan (late 7th century), which has been designated as a UNESCO world heritage site. Comparing the analytical results with those of a modern wood sample of the same species, the ageing process of archaeological wood was clarified as a change in the state of order on a macromolecular structural level. It can be concluded from NIR spectra that the amorphous region, and partially semi-crystalline region, in cellulose, hemicellulose, and lignin decreased by the ageing degradation, whereas the crystalline region in cellulose was not affected by the ageing. The accessibility of the diffusant to effect H/D-exchange was monitored by an OH-related absorption band obtained from FT-NIR transmission spectroscopy and characteristically varied with the ageing process of the wood samples, the absorption bands characteristic of a specific state of order and the diffusion agent. Finally, we proposed a morphological model to describe the variation of the fine structure of the microfibrils in the cell wall with ageing degradation. The state of microfibrils changed loosely by ageing, so that elementary fibrils were arranged loosely under 5 A, whereas several elementary fibrils in the modern wood were arranged in very close proximity under 3 A to each other.