Correlation spectrometry

The observant reader will have realized by now that the above experiment, which is a type of frequency modulation, provides no additional information beyond the simple H spectrum of acetone. Actually, that is the beauty of that experiment it has all of the elements of a 2-D correlation experiment and we can completely follow the activity of the net magnetization vector for acetone using simple vectorial models. Let us turn this prototype pulse sequence into a general format for all 2-D experiments. If we replace the first v/2 pulse with a generalized pulse that contains one or more pulses 

FIGURE 5.7 Generalized pulse sequence for 2-D NMR. The signal detected during acquisition, q, is modulated during the incremental time, q, thus giving rise to cross peaks in the 2-D spectrum. 

We now perform our second series of Fourier transformations on each of the 1024 interferograms to pro- 

The observant reader will have by now realized that the above experiment, which Derome (1987) calls frequency labeling, provides no additional information beyond the simple H spectrum of chloroform. Actually, 

If we return to our prototype 2-D experiment and apply this pulse sequence to an AX system, we will be in a better position to appreciate the incremental time, q. While we can describe mathematically precisely how the spins evolve during this time, we cannot show this evolution pictorially with vector diagrams. (The mathematical description for this system requires quantum mechanics and solution of the density matrix, well beyond the scope of this text.) After the first 7t/2 pulse, the system can be described as a sum of two terms each term contains the spin of only one of the two protons. During the time q, the spins precess (evolve) under the influences of both chemical shifts and their mutual spin-spin coupling. The mutual coupling has the effect of changing some of the individual spin terms into prod- 

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Fig. 16.10 Plot showing kinetics of C CljNOj reduction (fiUed circles) occurring in conjunction with increasing photon correlation spectrometry (PCS) count rates (open circles), which are indicative of particle formation, in reaction with O.SOmM Fe(ll) (pH 7.0). (For clarity, the symbols showing measured values of [C CljNOJ are connected point to point.) The other open symbols show PCS count rates in nonreaction mixtures (i.e., without C Cl NO ) containing either O.SOmM Fe(II) (pH 7.0) or O.SOmM Ca(ll) (pH 7.0). Reprinted with permission from Klupinski TP, Chin YP, Traina SJ (2004) Abiotic degradation of pentachloronitrobenzene by Fe(ll) Reactions on goethite and iron oxide nanoparticles. Environ Sci Technol 3S 4353-4360. Copyright 2004 American Chemical Society...

By its nature, correlation spectrometry poses a challenge even at the graduate level, as do the latter problems in Chapter 9 that depend heavily on correlated spectra. 

Carbon Monoxide. Methods for determining carbon monoxide include detection by conversion to mercury vapor, gas filter correlation spectrometry, TDLAS, and grab sampling followed by gas chromatograph (GC) analysis. The quantitative liberation of mercury vapor from mercury oxide by CO has been used to measure CO (73). The mercury vapor concentration is then measured by flameless atomic absorption spectrometry. A detection limit of 0.1 ppbv was reported for a 30-s response time. Accuracy was reported to be 3% at tropospheric mixing ratios. A commercial instrument providing similar performance is available. 

The size and charge analysis was done using a Coulter DELSA 440SX (Coulter Beckman Corp., Miami, FL). This particular instrument measured the size distribution on the basis of photon correlation spectrometry (PCS) and was limited to particle diameters between 0.02 pm and 3 pm. Measurements were taken at four different angles simultaneously with 256-channel resolution each. Comparison of the spectra allowed for the detection of very small particles. The zeta potential was assessed on the basis of electrophoretic mobility (laser Doppler anemometry, LDA). This was defined as the particle velocity per unit of applied electrical field, with units usually given as pm s 1/V cm-1, while zeta potential is defined as the electrical potential between the bulk solution and the... 

The values thus estimated (Table 3.4) are in reasonable agreement with the hydrodynamic layer thicknesses on polystyrene latex measured by photon correlation spectrometry and ultracentrifugation [224]. 

Ferrimagnetic nanoparticles of magnetite (Fc304) in diamagnetic matrices have been studied. Nanoparticles have been obtained by alkaline precipitation of the mixture of Fe(II) and F(III) salts in a water medium [10]. Concentration of nanoparticles was 50 mg/ml (1 vol.%). The particles were stabilized by phosphate-citrate buffer (pH = 4.0) (method of electrostatic stabilization). Nanoparticle sizes have been determined by photon correlation spectrometry. Measurements were carried out at real time correlator (Photocor-SP). The viscosity of ferrofluids was 1.01 cP, and average diffusion coefficient of nanoparticles was 2.5 10 cm /s. The size distribution of nanoparticles was found to be log-normal with mean diameter of nanoparticles 17 nm and standard deviation 11 nm. 

A fundamental study was performed to demonstrate that flow FFF is a good alternative technique for the rapid measurement of protein diffusion coefficients [10]. The results obtained for 15 proteins were in good agreement (within 4%) with the literature data based on classical methods and a group of modern methods such as photon correlation spectrometry (PCS), laminar flow analysis, a chromatographic relaxation method, and analytical split-flow thin-cell (SPLITT) fractionation. The advantages of flow FFF are the high-speed separations and the calculation of D values directly from retention data. 

MBDC = ( )-Methyl 4-(methylthio)-3-butenyldithiocarbamate. (Z)-MBDC = (Z)-Methyl 4-(methylthio)-3-butenyldithiocarbamate. i-H-l C-COSY = Proton-Carbon Correlation Spectrometry. iH-lH-COSY = Proton-Proton Correlation Spectrometry. 

There are a number of techniques that can be used in the field. These include electrochemical sensors for gases such as O2 and SO2 and diffusive samplers containing immobilized reagents that produce a visible color change with visual detection on exposure to a specific chemical. Passive diffusion tubes can also be used for analyte preconcentration. Subsequent laboratory analysis is usually undertaken by thermal desorption coupled with GC. This approach is particularly useful for trace organic compounds such as polyaromatic hydrocarbons (PAHs) and VOCs. Spec-trometric techniques such as Fourier transform infrared (FTIR) spectrometry, correlation spectrometry, and the laser based LIDAR (light detection... 

A 75/25 butadiene-styrene latex with a total sohds content of 68%, produced by cold emulsion polymerisation reaction and subsequently concentrated and evaporated, was incrementally fractionated through the technique of fractionated creaming with sodium alginate. The fractions were analysed in relation to the average particle size by photon correlation spectrometry. 13 refs. 

J. Sandsten, H. Edner, S. Svanberg Gas imaging using infrared gas-correlation spectrometry. Opt. Lett. 21, 1945 (1996)... 

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