Probe sampling system

FIGURE 25.19 NIR absorbance spectra for polypropylene (PP) and nylon66 (N66) fiber types, static/bench-top vs. fiber-optic probe sampling systems, 1000 to 2200 mn. [Redrawn from information in Rodgers, AATCC Review, 2 27 (2002).]... 

Many years have passed since the early days of AFM, when adhesion was seen as a hindrance, and it is now regarded as a useful parameter for identification of material as well as a key to understanding many important processes in biological function. In this area, the ability of AFM to map spatial variations of adhesion has not yet been fully exploited but in future could prove to be particularly useful. At present, the chemical nature and interaction area of the AFM probe are still rarely characterized to a desirable level. This may be improved dramatically by the use of nanotubes, carbon or otherwise, with functionalized end groups. However, reliance on other measurement techniques, such as transmission electron microscopy and field ion microscopy, will probably be essential in order to fully evaluate the tip-sample systems under investigation. 

Figure 4.1 Double-wheel sampling system and head of chemical ground probe on the back of the XM1135 Stryker NBCRV Hull. (Image modified from original supplied by the US Army.)...

Unlike electrostatic forces, chemical forces between the probing tip and the probed surface have been shown to profoundly affect the tunneling current from a certain onset. Owing to the advent of first-principle methods and powerful computers, it could finally be resolved by a calculation of the combined tip-sample system [ 15 ]. The point of onset for chemical bonding on metals was found to be at a distance of 4—5 A. As the tip approaches the surface, chemical forces rapidly become large enough to... 

Orientation Determination. While polarized edge studies, together with a known sample orientation, can provide information about the electronic structure of the absorber, one can also use polarized edges to probe ordered systems of unknown orientation. This sort of approach was used in a study of B adsorbed on graphite (26,27). In this case, the orientational dependence of an edge transition was used to calculate the degree of orientational purity of the graphite surface. 

The most straightforward tool for the introduction of a sample into a mass spectrometer is called the direct inlet system. It consists of a metal probe (sample rod) with a heater on its tip. The sample is inserted into a cmcible made of glass, metal, or silica, which is secured at the heated tip. The probe is introduced into the ion source through a vacuum lock. Since the pressure in the ion source is 10-5 to 10-6 torr, while the sample may be heated up to 400°C, quite a lot of organic compounds may be vaporized and analyzed. Very often there is no need to heat the sample, as the vapor pressure of an analyte in a vacuum is sufficient to record a reasonable mass spectrum. If an analyte is too volatile the cmcible may be cooled rather than heated. There are two main disadvantages of this system. If a sample contains more than one compound with close volatilities, the recorded spectrum will be a superposition of spectra of individual compounds. This phenomenon may significantly complicate the identification (both manual and computerized). Another drawback deals with the possibility of introducing too much sample. This may lead to a drop in pressure, ion-molecule reactions, poor quality of spectra, and source contamination. 

The pump-probe method provides the solution to this nanosecond barrier. Here, two light pulses are generated one to excite the sample (prepare the excited state) and one to probe the system at a given time after excitation (Figure 10.8). 

What issues concerning sample system or probe fouling and process stream filtration or coalescing need... 

In the case of HR-NMR the main stipulation is that all samples introduced to the analyzer must be in an entirely liquid form in order for the protons in the entire molecular distribution to be observed. Solids will not provide observable H signals and their presence will therefore reduce the efficacy of the on-line predictions or the model development. A sampling tap from the process lines must deliver separate streams (up to five) to the sample system at a flow rate of 260-340 liters per hour. The sample system must be designed to provide each sample stream to the NMR probe with a temperature variation of less than 3°C. Each sample system is custom designed to meet the above criteria by working in close collaboration with process engineers on the temperature, flows, pressures, viscosities, and solids content found in the various process lines. 

Samples must be physically brought to the NMR magnet and probe via a sample line and sampling system. This limits the number of streams that a single NMR unit can effectively moiutor with a useful duty cycle. Heating of samples entering the NMR analyzer is required for several reasons ... 

Sampling system, which consists of a sample turntable and moving articulated aspiration probe, and differs very Httle from the generic designs. 

Fluid sampling systems generally consist of four main sections, viz. the probe, the sample line, sample treatment and sample disposal. 

Some analyzers do not use a sampling system the analyzer probe is put directly into the process line. Many spectroscopic analyzers can be operated with a probe directly interfaced with the process (called in-line analysis). Some concerns with taking this approach are calibration, and how to introduce a real standard to the system for instrument verification. These are questions one must be asking. 

Microscopes used in LM are composed of a beam of visible light (photons) that represents the illumination source (probe), a system for focusing the source onto the sample (the condenser or condense glass lens), a location to place the sample or specimen, and the objective. 

In alternative energy processes, in most cases the goal is to eliminate all sampling systems and place the analyzer directly into the process. The "in-line" analyzer designs are widely available, and the various radiant energy and probe-type sensors operate without any sampling. 

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