Cooling probes

Temperature can destroy the piezoelectric properties of the probe, although techniques for cooling probes (delay blocks), and development of temperature-resistant piezoelectric materials, are extending the temperature range. Differences of up to 5% in thickness can occur between hot and cold readings. 

Sample Introduction and Transfer System. The sample Introduction and sample transfer system is a lengthened version of the PHI Model 15-720B Introduction system which consists of a polymer bellows-covered heating and cooling probe, a transferable sample holder, an eight-port dual-axis cross, and the mlnlreactor Interface port and transfer probe (Figure 2). There Is also a transfer vessel port with the necessary transfer probe for Introduction of air sensitive samples. They are not part of the reactor/surface analysis system. The dual cross and attached hardware are supported by the probe drive mechanism which floats on a block driven vertically and transversely by two micrometers. These micrometers plus the probe drive mechanism allow X-Y-2... 

Gas samples were taken from two positions in the apparatus two water-cooled probes were employed in the fuel bed and one water-cooled probe in the stack. 

Argon was used as the central plasma gas and as the sheath gas, as well. Reagent (H2) or auxiliary (O2) gases were mixed to the sheath gas. Powders were injected axially into the hottest region of the plasma by a PRAXAIR powder feeder through a water cooled probe. Both the raw materials and the products were characterized in terms of particle size, chemical and phase compositions. In each run products were collected from the reactor wall (R), from the reactor bottom (RB) and the cyclone (C). 

NOM and in turn provide key information as to the transformation and reactivity of NOM in the environment. Increased detection limits afforded by cryogenically cooled probes will be especially beneficial in this area. 

The development of cryogenically cooled probes has significantly decreased sample amount requirements for H NMR. Thermal noise in the probe and the first-stage receiver electronics dominate noise in NMR experiments. These new probes have built in first-stage receivers and rf coils that are cryogenically cooled ( 20°K), and have S/N improvements of 4 X standard probes. It is obvious to users that the highest field instrument available provides the best sensitivity. For fixed concentration (N), we would need 2.8 times as much material with a 300 MHz as on a 600 MHz system to obtain spectra with identical S/N ... 

The incredible natural abundance double quantum transfer experiment (INADEQUATE) was proposed by Ray Freeman in 1980.1 2 The acronym of this remarkable technique sat high among the many NMR acronyms since, at the time of its birth, it accurately described all its attributes. INADEQUATE was seen as an incredible experiment with vast potential its widespread applications are dwarfed only by its inadequate sensitivity. Depending on the equipment available, an ovemight-to-weekend INADEQUATE experiment on a medium-sized molecule would typically require hundreds of milligrams of sample. Only recently have such unfavourable requirements been addressed with advent of cryogenically cooled probes. Now, INADEQUATE experiments using samples of 5-10 mg have become realistic propositions. 

INADEQUATE in the field of high-resolution NMR is still mainly applied to the establishment of carbon-carbon connectivities, but its application to other nuclei continue to appear in the literature sporadically. Improvements in the sensitivity comparable to those offered by 1H- or 13C-optimised cryogenically cooled probes would undoubtedly increase the usage of INADEQUATE for non-carbon nuclei significantly. 

Niobium pentachloride decomposes readily in the presence of moisture thus it is very important in this synthesis that the acetonitrile be rigorously dried. The method described by Coetzee et al.1 is suitable for the purification of this solvent. The niobium pentachloride starting material should also be freed of any oxy species. This can be effected at about 100° by sublimation of the pentachloride away from the less volatile oxychlorides using a standard vacuum sublimer with a water-cooled probe. Appearance of commercial samples is a poor guide to their purity, and this purification step should not be omitted. The potassium thiocyanate should be purified by recrystallization and then thoroughly dried. 

The checker found it more convenient to sublime the impure /-C5H5Mn(CO)2(C8Hi4) after removal of unreacted /-C5H5Mn(CO)3. In this way, a brown crystalline material, not a gum, is obtained after removal of CSa. The product can then be directly sublimed at 30° onto a water-cooled probe to produce the pure thiocarbonyl. 

The combustor inlet air pressure was fixed at 10 atm and the temperature at 530 K. The fuel temperature at injection was maintained between 340 and 360 K. The burner was operated at an overall fuel-air mixture ratio of 0.014, corresponding to normal power (40,000 hp) operation of the FT4 gas turbine. Traversing stainless steel, water-cooled probes were... 

Combustion Gas Sample Probe and Sample Analysis. Combustion gas composition was analyzed on-line by means of a water-cooled probe, an electrically heated sample transfer line, and a so-called emission analysis bench. Gas samples were analyzed on a dry volumetric basis for O2, CO2, NOaj, CO, and unbumed HC. 

Cooling probes are commonly found in constant temperature baths, when a temperature below ambient temperature is required, and probes can be used instead of solid CO2 to produce temperatures down to -100 °C. CooHng probes are expensive pieces of equipment therefore you will find them dedicated to a specific experiment and they are not usually available for basic laboratory operations. 

A sublimation apparatus (with a water-cooled probe) is charged with 4.0 g of carbonyltetrakis(trimethylphosphine)iridium(I) chloride, evacuated, and heated to 130°. At first a white film appears on the cold finger, followed by growth of bright yellow crystals. After nearly all the solid has sublimed, the product is scraped from the cold finger (this may be done in air, but exposure should be kept to a minimum) and resublimed once or twice until the sublimate consists of pure yellow crystals with no visible white contaminant. The yield is 2.4 g (87%).+ Anal. Calcd. for C7H,8ClIrOP2 C, 20.6 H, 4.46. Found C, 21.10 H, 4.55. 

Styles, P. Soffe, N.E. Scott, C.A. An improved cryogeni-cally cooled probe for high-resolution NMR. J. Magn. Reson. 1989, 84, 376-378. 

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