Sample cryogenic cooling system

Alternatively, air collected in a SUMMA passivated stainless steel canister either by pressurizing the canister using a sample pump or by preevacuating canister then connected to an analytical system air transferred to a cryogenically cooled trap cryogen removed and temperature raised analyte revolatilized separated on a GC column determined by PID, FID, or a mass spectrometer (U.S. EPA Method TO-14, 1988). 

Adsorbed over carbon molecular sieve (-400 mg) desorbed at 350°C into a cryogenically cooled trap flash evaporated onto a capillary column GC/MS system recommended sample volume 10 L flow rate 100 mL/min. Collected in SUMMA passivated canister or a liquid argon trap transferred onto a precooled GC column determined by ECD or MSD. 

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 ... 

Probes usually have variable temperature control to run experiments at temperatures selected by the analyst. Cryogenically cooled probes can improve the resolution of a system, so that a 600 MHz spectrometer equipped with such a probe can provide resolution equivalent to a 700-800 MHz instrument. New probe designs with flow-through sample holders are commercially available, for use in coupled HPLC-NMR instruments and HPLC-NMR-MS instruments. These hyphenated instruments are discussed under applications later in the chapter. 

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