Situ Analysis

During the synthesis stages of silicate-1, several intermediate crystallites of different size ranges are known to be involved and this difference in size necessitates 

Every analytical instrument has its own restriction on its use for analysis so, a truly in situ measurement under identical synthesis condition may not be always possible. In other words, often compromises have to be made. However, it is possible to work around this problem by adapting the reaction conditions. Examples include the synthesis of sihcahte-l at room temperature [23], or by looking at the reverse process, that is, the dissolution of silicalite-1 crystals [27]. Much insight could also be obtained by these approaches. Here, however, we choose to focus on measurements where the analysis technique has been adapted to suit the hydrothermal reaction conditions, as this is the topic of this chapter. 

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It is becoming more and more desirable for the analytical chemist to move away from the laboratory and iato the field via ia-field instmments and remote, poiat of use, measurements. As a result, process analytical chemistry has undergone an offensive thmst ia regard to problem solviag capabihty (77—79). In situ analysis enables the study of key process parameters for the purpose of definition and subsequent optimization. On-line analysis capabihty has already been extended to gc, Ic, ms, and ftir techniques as well as to icp-emission spectroscopy, flow iajection analysis, and near iafrared spectrophotometry (80). 

A wide variety of particle size measurement methods have evolved to meet the almost endless variabiUty of iadustrial needs. For iastance, distinct technologies are requited if in situ analysis is requited, as opposed to sampling and performing the measurement at a later time and/or in a different location. In certain cases, it is necessary to perform the measurement in real time, such as in an on-line appHcation when size information is used for process control (qv), and in other cases, analysis following the completion of the finished product is satisfactory. Some methods rapidly count and measure particles individually other methods measure numerous particles simultaneously. Some methods have been developed or adapted to measure the size distribution of dry or airborne particles, or particles dispersed inhquids. 

Prechromatographic dansylation has the advantage that chromatography separates excess reagent and also the fluorescent by-products (e g dansyl hydroxide) from the reaction products of the substances to be determined In the case of postchromatographic dansylation the whole of the plate baekground fluoresees blue, so that in situ analysis is made more diflicult... 

More sensitive detection methods and more objective recording methods (e g the employment of scanners) are constantly been striven for m order to overcome this illusion It IS for this reason too that fluorescent methods have been introduced to an increasing extent on account of their higher detection sensitivity This allows an appreciable reduction in the amount of sample applied, so that possible interfering substances are also present m smaller quantibes This increases the quality of the chromatographic separation and the subsequent m situ analysis... 

Unfortunately, only thin films of about 20 nanometers in thickness could be obtained with Gel4 An ex situ analysis was difficult, because of experimental limitations, but XPS clearly showed that elemental Ge was also obtained, besides... 

These forms are useful if [L] is known, either from an in situ analysis (e.g., a chloride ion electrode to measure [Cl-]) or because the experiment was designed with [L] [A]. If, on the other hand, the concentration of free A is known or more eas-... 

In situ analysis of the reaction products can also be carried out by mass spectrometry, using the differential electrochemical mass spectrometry (DBMS) technique.This technique permits the detection of gaseous products since they are produced and captured through a porous electrode. It has been confirmed that carbon dioxide is the main reaction product. With this technique, it is also possible to determine the production of CO2... 

Hess A, B Zarda, D Hahn, A Haner, D Stax, P Hohener, J Zeyer (1997) In situ analysis of denitrifying toluene-and m-xylene-degrading bacteria in a diesel fuel-contaminated laboratory aquifer column. Appl Environ Microbiol 63 2136-2141. 

Based on electrochemical experiments combined with ex situ analysis by AES, LEED, and RHEED, Wang et al. (2001) suggested the formation of a (2 x 2) (2CO + O) adlayer on Ru(OOOl) at = 0.2 V in CO-samrated HCIO4, similar to the phase formed in UHV after CO adsorption on a (2 x 2)0-covered surface [Schiffer et al., 1997]. Erom the total charge density transferred after a potential step to 1.05 V in a CO-free electrolyte, they concluded that only 60% of the CO content in such an adlayer can be oxidized under these conditions [Wang et al., 2001]. 

SIMS has also been successfully applied for thorium isotopic measurement during the past decade. This technique has been applied for both chemically separated thorium samples (England et al. 1992 Bourdon et al. 1994 Layne and Sims, 2000), as well as in-situ analysis of minerals with high thorium content such as zircons (Reid et al. 1997). 

SIMS techniques have occupied somewhat of a narrower niche in uranium-series analysis, but have significantly improved Th isotope analysis relative to TIMS for chemically separated samples. The major improvement relative to TIMS is an improvement by about an order of magnitude in efficiency or sample size requirements for silicates. For uranium and/or thorium rich minerals such as carbonates and zircons, both SIMS and laser-ablation MC-ICPMS have been used for the direct in situ analysis of U and Th isotopes (Reid et al. 1997 Stirling et al. 2000) on very small (pg to ng levels of total U and Th) samples, at 10-100 pm scale resolution. 

Principles and Characteristics Vibrational spectroscopic techniques such as IR and Raman are exquisitely sensitive to molecular structure. These techniques yield incisive results in studies of pure compounds or for rather simple mixtures but are less powerful in the analysis of complex systems. The IR spectrum of a material can be different depending on the state of the molecule (i.e. solid, liquid or gas). In relation to polymer/additive analysis it is convenient to separate discussions on the utility of FUR for indirect analysis of extracts from direct in situ analysis. 

Principles and Characteristics The prospects of Raman analysis for structural information depend upon many factors, including sample scattering strength, concentration, stability, fluorescence and background scattering/fluorescence from the TLC substrate. Conventional dispersive Raman spectroscopy has been considered as a tool for in situ analysis of TLC spots, since most adsorbents give weak Raman spectra and minimal interference with the spectra of the adsorbed species. Usually both silica and cellulose plates yield good-quality conventional Raman spectra, as opposed to polyamide plates. Detection limits for TLC fractions... 

Martinez-Arias, A., Fernandez-Garcia, M., Iglesias-Juez, A. et al. (2001) New Pd/CexZrj x02/Al203 three-way catalysts prepared by microemulsion Part 2. In situ analysis of CO oxidation and NO reduction under stoichiometric CO + NO + 02, Appl. Catal. B Environ., 31, 51. 

Coupling an electrochemical cell to an analytical device requires that hindering technical problems be overcome. In the last years there has been a considerable improvement in the combined use of electrochemical and analytical methods. So, for instance, it is now possible to analyze on-line electrode products during the simultaneous application of different potential or current programs. A great variety of techniques are based on the use of UH V for which the emersion of the electrode from the electrolytic solution is necessary. Other methods allow the in situ analysis of the electrode surface i.e the electrode reaction may take place almost undisturbed during surface examination. In the present contribution we shall confine ourselves to the application of some of those methods which have been shown to be very valuable for the study of organic electrode reactions. 

IR reflectance allows the in situ analysis of the electrode-electrolyte interface [8, 9], The Fourier transform variant adds to this technique the advantage of very fast data collection [10],... 

The recently developed ex situ analysis of electrode ad-layers by thermal desorption mass spectroscopy has been demonstrated to be a powerful tool for the study of adsorbates [13, 14],... 

Manz, W. In situ analysis of microbial biofilms by rRNA-targeted oligonucleotide probing. Methods Enzymol. 1999,310,79-91. 

Three methods for quantitative analysis of niclosamide at concentrations of 0.5-2.0 ppm were given. For in situ analysis, safranine dye solution was added to the sample and the extraction solution added which formed the upper phase. The niclosamide content was determined by the color intensity of the upper phase. The colors were compared with blanks of known concentration. When an accurate determination was required, niclosamide was extracted from the water sample with amylacetate, a methanol solution of sodium hydroxide was added to the extraction, and the resulting yellow color was measured at 385 mft in a spectrophotometer. Third method made use of a calibration curve [60],... 

Infrared microscopy is well suited for in situ analysis of contaminants fount in pharmaceutical processes. Due to the nondestructive nature of the analysis further experiments such as energy dispersive x-ray analysis may be performer on the same sample once IR investigations are complete. To illustrate the potentia of IR microspectroscopy, one application from the Bristol-Myers Squibl laboratories is presented. 

Prior to the introduction of ion-selective electrode techniques, in situ monitoring of free copper (II) in seawater was not possible due to the practical limitations of existing techniques (e.g., ligand competition and bacterial reactions). Ex situ analysis of free copper (II) is prone to experimental error, as the removal of seawater from the ocean can lead to speciation of copper (II). Potentially, a copper (II) ion electrode is capable of rapid in situ monitoring of environmental free copper (II). Unfortunately, copper (II) has not been used widely for the analysis of seawater due to chloride interference that is alleged to render the copper nonfunctional in this matrix [288]. 

Megrue, G. H., Distribution and Origin of Helium, Neon, and Argon Isotopes in Apollo 12 Samples by n Situ Analysis with a Laser-Probe Mass Spectrometer, J. Geophys. Res. 76, 4956 (1971). 

A closer examination by ex situ analysis using NMR or gas chromatography illustrates that intrazeolite reaction mixtures can get complex. For example photooxygenation of 1-pentene leads to three major carbonyl products plus a mixture of saturated aldehydes (valeraldehyde, propionaldehyde, butyraldehyde, acetaldehyde)38 (Fig. 33). Ethyl vinyl ketone and 2-pentenal arise from addition of the hydroperoxy radical to the two different ends of the allylic radical (Fig. 33). The ketone, /i-3-penten-2-one, is formed by intrazeolite isomerization of 1-pentene followed by CT mediated photooxygenation of the 2-pentene isomer. Dioxetane cleavage, epoxide rearrangement, or presumably even Floch cleavage130,131 of the allylic hydroperoxides can lead to the mixture of saturated aldehydes. 

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