摘要:

Subtractive polarography is a differential polarographic technique that allows the measurement of wanted signals in the presence of unwanted signals. The technique requires two polarographic cells, with DME's operated at the same potential. The “unknown” solutionis placed in one cell and gives rise to the total current. The solution in the second cell contains those components of the “unknown” solution that give rise to the unwanted portion of the total signal. Measurement of the difference between the polarographic currents at the electrodes in the two solutions thus yields the wanted portion of the total signal. This technique has been evaluated with a controlled-potential differential dc polarograph that utilizes dropping-mercury electrodes having uncontrolled drop times, and the results are presented in this paper. The results indicate that subtractive polarography affords improved sensitivity, selectivity, and resolution over that of conventional dc polarography, and an improvement in resolution over that of derivative polarography. An additional improvement in resolution can be achieved by means of derivative subtractive polarography.

ISSN:1073-9149    

DOI:10.1080/10739146808545753

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

To investigate an alternative to the method of determining the relative abundance of isotopes by mass spectroscopy or X-rays, use of the structure of satellites accompanying the proton magnetic resonance spectra of metal chelates is proposed. In particular, the relative abundance of the lead-207 isotope was determined by the NMR method. The proton NMR spectrum of aqueous solutions of lead-EDTA chelate presents two signals corresponding to ethylenic and acetate protons. Each of these is accompanied by a pair of symmetric satellites, due to the coupling of these protons with lead-207. Since other lead isotopes—204, 206, and 208—have zero spin quantum numbers, they give a single line at the center of the satellites. The isotopic abundance of lead-207 can be determined by a comparison of the relative intensities of the satellites and the central line. A detailed examination of the experimental conditions was performed to find the most suitable conditions for measurements.

ISSN:1073-9149    

DOI:10.1080/10739146808545754

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

A bridge-type high-resolution NMR spectrometer has been modified to yield a triple-resonance spectrometer which decouples two kinds of interaction,14N-1H and1H-1H. The instrumentation of this modification is described in detail. The conditions for decoupling the UN interaction with proton were investigated experimentally, especially the dependence of the proton resonance resolution on both power and frequency of the rf field corresponding to the UN resonance. It is pointed out that the resonance frequency of the14N nucleus can be measured with high accuracy using this double-resonance technique. The triple-resonance technique was applied to pyrrole, and was successful in obtaining the finely resolved spectrum and in attributing the spin-spin couplings to the interactions between specified groups of proton.

ISSN:1073-9149    

DOI:10.1080/10739146808545755

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The introduction of the laser as an excitation source in Raman spectroscopy offers numerous new possibilities of investigations but demands the design of new types of sample cells specially suited for laser application. Two cells for work with molten salts corrosive to glass and quartz and a simple cell for melts noncorrosive to glass are described. The best results are obtained with a cell which provides total utilization of the laser energy for excitation by multiple reflection of the laser beam. In addition, some necessary accessories for molten salt work, i.e., a gas heater and filtration equipment to free the melt of suspended impurities which might cause an undesirable level of Tyndall and Rayleigh scattering, are mentioned.

ISSN:1073-9149    

DOI:10.1080/10739146808545756

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Many of the optical, electrical, and mechanical components andsystems of a recording spectropolarimeter may be used in adapting the spectropolarimeter to measure and record circular dichroism. This article describes the construction and performance characteristics of an accessory for the measurement of circular dichroism in the 6000-1850 A region on a commercially available recording spectropolarimeter, the Cary Instruments Model 60. The accessory employs an improved version of the electro-optic modulator technique. It consists of four units which are easily coupled to the spectropolarimeter. Furthermore, conversion of the spectropolarimeter to the standard mode of operation is readily achievable.

ISSN:1073-9149    

DOI:10.1080/10739146808545757

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

A versatile luminescence spectrophotometer has been designed and constructed. With this instrument, corrected excitation and emission spectra are recorded automatically in either relative energy or quantum units without loss of resolution or sensitivity. Quantum efficiencies of luminescence are determined directly or by comparison of unknowns with a compound of known quantum efficiency. The instrument covers the spectral range 200-1250 μ with interchangeable gratings and detectors. Low-temperature measurements of fluorescence and phosphorescence are made using aquartz Dewar. Luminescence decay curves are measured to rates approaching 1 msec. High-resolution spectra can be obtained: to ˜ 2 Å between 200 and 750 mμ, and ˜ 10 Å between 750 and 1250 mμ The sample chamber is adaptable to allow for measurement of luminescence of solutions, frozen solutions, solid matrices, crystals, etc. The utility of the instrument for most of these uses is demonstrated.

ISSN:1073-9149    

DOI:10.1080/10739146808545758

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Apparatus capable of linearly programming the temperature of a gaschromatographic column at up to 400°C/min is described. In the apparatus the column tube wall is directly heated with an electric current. Variation in temperature along the column is negligible. A commercially available temperature programmer may be modified not only to provide a variety of high linear-programming rates but also to provide for remote program initiation and event marking.

ISSN:1073-9149    

DOI:10.1080/10739146808545759

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The ORNL Analytical Chemistry Division has developed a partially automated procedure for assay of transfer ribonucleic acids that utilizes the reaction between a tRNA and a14C-tagged amino acid, followed by precipitation and counting of the reaction product on a filter-paper disk. In this procedure, a Technicon AutoAnalyzer is used to take tRNA samples, mix them with the amino acid and suitable buffers and enzymes, and incubate the mixture. After incubation, segments of ca. 56-[I volume are transferred from the AutoAnalyzer output stream to small filter-paper disks by an output sampler of our design. This is done by alternately pressing the tip of the output tube against a paper disk for a measured time, and against the orifice of a waste aspirator. The output sampler is synchronized with the Technicon input sampler by using a dye in the rinsing solution that is picked up between samples at the input; barren zones of the product stream are colored, and sample-rich zones remain nearly colorless. The color actuates a photometric meter relay, whose operating point may be set for either the rise or fall of color in the stream. Once the relay has closed, it will remain so until one sample sequence is completed: an initial delay of 60 sec (or less) may be introduced to ensure that the sampling period spans a peak input-sample concentration. After the delay, a cam driven by a synchronous motor moves the output tip from the waste aspirator into contact with apaper disk. As this cam completes its revolution, it switches a second cam-driving

ISSN:1073-9149    

DOI:10.1080/10739146808545760

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Linear potential sweep voltammetry at stationary or quasi-stationary electrodes has become a widely accepted analytical technique. In contrast with the well-known dc polarographic current-voltage curve which reaches a limiting current (i1) at potentials sufficiently removed from the half-wave potential (E1/2), the voltammetric curve at a stationary electrode in unstirred solution reaches a maximum value (ip) after which the current decreases rather slowly as the potential is increased further. This “tail” is a matter of concern in the analysis of multicomponent systems if two or more species react during a single sweep of the electrode potential. This communication presents the results of calculations made to determine the separation of half-wave potentials required to permit the quantitative determination of each species in multicomponent systems. Regular, first-, and second-derivative techniques are considered.

ISSN:1073-9149    

DOI:10.1080/10739146808545761

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The current interest in the kinetics of electrode processes was historically preceded by a consideration of electrochemical thermodynamics. The thermodynamic experiments consisted of the equilibrium (zero current) measurement of cell potentials as a function of temperature. Measurements were also made of the temperature changes associated with the charging and discharging of cells.

ISSN:1073-9149    

DOI:10.1080/10739146808545762

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor