Probe insert

Liquids examined by FAB are introduced into the mass spectrometer on the end of a probe inserted through a vacuum lock in such a way that the liquid lies in the target area of the fast atom or ion beam. There is a high vacuum in this region, and there would be little point in attempting to examine a solution of a sample in one of the commoner volatile solvents such as water or dichloromethane because it would evaporate extremely quickly, probably as a burst of vapor when introduced into the vacuum. Therefore it is necessary to use a high-boiling solvent as the matrix material, such as one of those listed in Table 13.1. 

An Omega model HH22 type J-K digital thermometer, connected to a type K thermocouple probe inserted directly into the flask, was used to measure the temperature. 

When FAB is utilized for FC-MS, often known as continuous-flow FAB, a matrix material is added to the HPFC eluent, either pre- or post-column, and this mixture continuously flows to the tip of a probe inserted into the source of the mass spectrometer where it is bombarded by the atom beam (Figure 3.3). 

When the aim is isolation for identification by direct probe insertion mass spectrometry (MS), plastic materials, filter papers, and blenders should be avoided to prevent contamination during extraction and chromatography. It is also very important to avoid the cis-trans isomerization of carotenoids in solution, which is accelerated by heat, light, acids, and active surfaces. Therefore, a pure carotenoid or even a crude extract should never be stored in solution it should be kept completely dry in an inert atmosphere at low temperature. 

Neutron attenuation Emits high-energy neutrons into the soil that collide with hydrogen atoms associated with soil water and counts the number of pulses, which is correlated to moisture content Consists of a probe inserted into access boreholes with aluminum or polyvinyl chloride casing... 

Most spectrometers measure the magnetic field by a Hall effect probe consisting of a sensor mounted on one of the pole faces of the magnet. However, such estimates of the value of B inside the cavity are not sufficiently accurate to be used for g-factor determinations. There are two ways around this problem (i) measure the spectrum of a solid free radical such as dip-henylpicrylhydrazyl (DPPH), which has a well-known g-value (2.0028), at least once during acquisition of the desired spectrum or (ii) use of an NMR gaussmeter probe inserted in or near the cavity several times during the collection of the spectrum. 

Volatile or volatilizable compounds may be introduced into the spectrometer via a pinhole aperture or molecular leak which allows a steady stream of sample molecules into the ionization area. Non-volatile or thermally labile samples are introduced directly by means of an electrically heated probe inserted through a vacuum lock. Numerous methods of sample ionization are available of which the most important are electron impact (El), chemical ionization (CY), field ionization (FI), field desorption (FD), fast atom bombardment (FAB), and radio-frequency spark discharge. 

Measurements were made by first calibrating the pH probe using two buffer solutions at pH s of 7 and 10 supplied by Van Labs of Van Waters and Rogers Equipment Company. These solutions have been certified by the National Bureau of Standards to be accurate to + 0.01 pH unit at 25°C. This pH calibration was made with the probe inserted in buffer solution at the same temperature as the pH measurements were made. 

Fig. 8.8. FD probe inserted into the vacuum lock. FD probes are generally inserted in axial position to leave the vacuum lock of the DIP free for FI use. The emitter wire is now oriented vertically to comply with the beam geometry of the magnetic sector analyzer.

Camp DM, Robinson TE. 1992. On the use of multiple probe insertions at the same site for repeated intracerebral microdialysis experiments in the nigrostriatal dopamine system of rats. J Neurochem 58(5) 1706-1715. 

An alternative arrangement would involve a number of probes inserted through the walls of a vessel allowing a much larger sonochemical treatment zone. Such a system will suffer from the same problems as the individual flow cell except that it will continue to function even if one or two probe units fail (Fig. 7.18). 

The extmders were monitored using a pair of custom-made transmission probes inserted into the extruder die just downstream from the screws. Each probe consisted of a sapphire window brazed into a metal body a quartz rod behind the window piped the light to the end of the probe low-OH silica fiber-optic bundles connected the probe to the NIR analyzer, an LT Quantum 12001. Optical path lengths were typically between 0.3 and 2.0 cm. 

Body Temperature Determination. Unless otherwise noted, experiments were carried out at 2k°C (room temperature) and no attempt was made to individually cage the treated or control animals. For the elevated temperatures of 28°C, 3U°C and 3T C, animals were acclimated to the desired temperature for 2k h. Temperatures of the mice were taken using a YSI temperature probe inserted approximately 20 mm into their rectum. The initial temperatures (recorded as zero time) were taken immediately before administration of the extracts. 

Fig. 38. Temporal evolution of temperature probes inserted in a regenerating DPF (bottom) along with the spatial distribution of filter temperature at 145 s, i.e. the moment of exothermic peak (top). Locations (r,z) in millimeter of temperature probes Probe 1, (24.25,40) and Probe 2, (24.25,142) (see Plate 13 in Color Plate Section at the end of this book).

The potential of the negative chemical-ionization (n.c.i.) technique for obtaining valuable structural information on very small samples of underivatized oligosaccharides has been demonstrated.200 The n.c.i. spectra of several mono-, di-, tri-, and tetra-saccharides were recorded, using methane as the reagent gas, and direct-probe insertion of the samples into the ion source.201 Fairly intense, molecular ions, M-, were observed in each case. A small number of fragment ions were also observed, but could not be interpreted. Use of dichlorodifluoro-... 

Sequence of events in matrix-assisted laser desorption/ionization. (a) Dried mixture of analyte and matrix on sample probe inserted into backplate of ion source. (foZ) Enlarged view of laser pulse striking sample. (t>2) Matrix is ionized and vaporized by laser and transfers some charge to analyte. (b3) Vapor expands in a supersonic plume. 

Neyroz et al. [97] have covalently linked 2NpOH to phos-phatidylethanolamine moiety by the Schiff-base formation between the NH2 of the phospholipid and the aldehyde moiety of 2-hydroxy-1-naphthaldehyde, followed by selective reduction of the imine to obtain a stable secondary amine. This fluorescent phospholipid easily incorporates into DML vesicle membrane and exhibits the typical behavior of ESPT probes. The emission spectrum of this probe inserted in the liposome is similar to that in ethanol medium and is affected by acetate used as a proton acceptor. 

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