Ambient spectroscopy

Schneider J, Erdelen C, Ringsdorf H and Rabolt J F 1989 Structural studies of polymers with hydrophilic spacer groups. 2. Infrared-spectroscopy of Langmuir-Blodgett multilayers of polymers with fluorocarbon side-chains at ambient and elevated temperatures Macromolecules 22 3475-80... 

Dyer R B, Einarsdottir 6, Killough P M, Lopez-Garriga J J and Woodruff W H 1989 Transient binding of photodissociated CO to of eukaryotic cytochrome oxidase at ambient temperature. Direct evidence from time-resolved infrared spectroscopy J. Am. Chem. Soc. Ill 7657-9... 

To examine a sample by inductively coupled plasma mass spectrometry (ICP/MS) or inductively coupled plasma atomic-emission spectroscopy (ICP/AES) the sample must be transported into the flame of a plasma torch. Once in the flame, sample molecules are literally ripped apart to form ions of their constituent elements. These fragmentation and ionization processes are described in Chapters 6 and 14. To introduce samples into the center of the (plasma) flame, they must be transported there as gases, as finely dispersed droplets of a solution, or as fine particulate matter. The various methods of sample introduction are described here in three parts — A, B, and C Chapters 15, 16, and 17 — to cover gases, solutions (liquids), and solids. Some types of sample inlets are multipurpose and can be used with gases and liquids or with liquids and solids, but others have been designed specifically for only one kind of analysis. However, the principles governing the operation of inlet systems fall into a small number of categories. This chapter discusses specifically substances that are normally liquids at ambient temperatures. This sort of inlet is the commonest in analytical work. 

Emission spectroscopy is the analysis, usually for elemental composition, of the spectmm emitted by a sample at high temperature, or that has been excited by an electric spark or laser. The direct detection and spectroscopic analysis of ambient thermal emission, usually ia the iafrared or microwave regioas, without active excitatioa, is oftea termed radiometry. la emission methods the sigaal iateasity is directiy proportioaal to the amouat of analyte present. 

When the spectral characteristics of the source itself are of primary interest, dispersive or ftir spectrometers are readily adapted to emission spectroscopy. Commercial instmments usually have a port that can accept an input beam without disturbing the usual source optics. Infrared emission spectroscopy at ambient or only moderately elevated temperatures has the advantage that no sample preparation is necessary. It is particularly appHcable to opaque and highly scattering samples, anodized and painted surfaces, polymer films, and atmospheric species (135). The interferometric... 

Historically, measurements have classified ambient hydrocarbons in two classes methane (CH4) and all other nonmethane volatile organic compounds (NMVOCs). Analyzing hydrocarbons in the atmosphere involves a three-step process collection, separation, and quantification. Collection involves obtaining an aliquot of air, e.g., with an evacuated canister. The principal separation process is gas chromatography (GC), and the principal quantification technique is wdth a calibrated flame ionization detector (FID). Mass spectroscopy (MS) is used along with GC to identify individual hydrocarbon compounds. 

All three techniques probe 500 A to 1 pm or so in depth for opaque materials, depending on the penetration depth of the incident light. For transparent materials, essentially bulk properties are measured by PL and Modulation Spectroscopy. All three techniques can be performed in ambient atmosphere, since visible light is used both as incident probe and signal. 

Raman spectroscopy is a very convenient technique for the identification of crystalline or molecular phases, for obtaining structural information on noncrystalline solids, for identifying molecular species in aqueous solutions, and for characterizing solid—liquid interfaces. Backscattering geometries, especially with microfocus instruments, allow films, coatings, and surfaces to be easily measured. Ambient atmospheres can be used and no special sample preparation is needed. 

In order to understand RAIR spectroscopy, it is convenient to model the experiment (see Fig. 4). Consider a thin film with refractive index n =n ik and thickness d supported by a reflecting substrate with refractive index ni = ri2 — iki- The refractive index of the ambient atmosphere is o- Infrared radiation impinges on the film at an angle of incidence of 6 . The incident radiation can be polarized parallel to or perpendicular to the plane of incidence. 

An initial solution was prepared by dissolving metallic niobium powder in 40% hydrofluoric acid. The dissolution was performed at elevated temperature with the addition of a small amount of nitric acid, HN03, to accelerate the process. The completeness of niobium oxidation was verified by UV absorption spectroscopy [21]. The prepared solution was evaporated to obtain a small amount of precipitate, which was separated from the solution by filtration. A saturated solution, containing Nb - 7.01 mol/1, HF - 42.63 mol/1, and corresponding to a molar ratio F Nb = 6.08, was prepared by the above method. The density of the solution at ambient temperature was p = 2.0 g/cc. Concentrations needed for the measurements were obtained by diluting the saturated solution with water or hydrofluoric acid. 

Well-defined CdS/CdSe superlattices have been formed by means of ECALE [74]. In these structures the CdS component - and not CdSe - suffered from substantial crystallographic strain as was evidenced by surface-enhanced Raman spectroscopy (SERS) - a valuable tool for characterizing the superlattice phonons in electrochemical or other ambient environments. Torimoto et al. reported quantum confinement in superlattices of ZnS/CdS grown by ECALE [75]. 

A relatively new arrangement for the study of the interfacial region is achieved by so-called emersed electrodes. This experimental technique developed by Hansen et al. consists of fully or partially removing the electrode from the solution at a constant electrical potential. This ex situ experiment (Fig. 9), usually called an emersion process, makes possible an analysis of an electrode in an ambient atmosphere or an ultrahigh vacuum (UHV). Research using modem surface analysis such as electron spectroscopy for chemical analysis (ESCA), electroreflectance, as well as surface resistance, electrical current, and in particular Volta potential measurements, have shown that the essential features (e.g., the charge on... 

Time-resolved spectroscopic techniques are important and effective tools for mechanistic photochemical studies. The most widely used of these tools, time-resolved UV-VIS absorption spectroscopy, has been applied to a variety of problems since its introduction by Norrish and Porter almost 60 years ago. Although a great deal of information about the reactivity of organic photochemical intermediates (e.g., excited states, radicals, carbenes, and nitrenes) in solution at ambient temperatures has been amassed with this technique, only limited structural information can be extracted from... 

The number average molecular weights, Mq, of the polymers obtained in Table II ranged from 1300 to 3900 as determined by vapor nressure osmometry (VPO), and they were further characterized by - -H- and C-NMR spectrometry at ambient temperature and at 90°C, as well as by IR spectroscopy. The homopolymers of isopropenylferro-cene were found to have the expected structure, P, shown below, obtained by polymerization through the isopropenyl units, as indicated by spectroscopic characterization ... 

A series of diastereomeric platinum(II) complexes of the type c -[PtL2Y2]2+ (L - 3-bromopyr-idine, quinoline, isoquinoline Y = PEt3, Y2 = dppp, (/ )-(I )-2,2 -bis(diphenylphosphino)-l, l -binaphthyl (R-( I )-binap)) have been prepared by the reaction of c -[PtY2(OTf)2] (OTf=tri-trifluoromethanesulfonate) with two equivalents of the N-donor ligand.207 Related complexes have also been studied, for example when L = pyridine.208 Restricted rotation about the Pt—N bonds in many of the complexes is usually detected by NMR spectroscopy, with only [Pt(dppp)(isoquinoline)2]2+ (65) exhibiting dynamic behavior at ambient temperatures. The PEt3... 

The spiroaziridinium salt was formed as a single diastereoisomer, as expected from the rearrangement and, although not isolated, was found to be stable for several days in ambient conditions. Its presence was confirmed by H NMR spectroscopy of the reaction mixture. 

The next question to address is to what extent does the study of a (deeply) frozen biological sample provide information that is relevant for an understanding of its functioning in a living cell at whatever the ambient temperature of this cell happens to be First and foremost, let us state the fact of experience that solutions of biomacromolecules such as metalloproteins can be frozen and thawed many times without any detectable deterioration of their biological activity. Combined with the rather low intensity (<0.2 W) of the microwave source of an EPR spectrometer, this leads to the proposition that EPR spectroscopy is a nondestructive technique. 

Having ascertained that low-temperature EPR is nondestructive, we can now address a fundamental follow-up question To what extent does the spectroscopy of a biomolecule at a temperature of, say, 10 K bear relevance to that same molecule s cellular functioning at its ambient temperature of, say, 310 K (=37°C). More specifically, to what aqueous solution conformation temperature, if any, does a frozen solution protein conformation correspond This now is a really hard question to answer, simply because it is difficult to approach experimentally, and consequently, there is... 

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