Back-flash procedure

Within the analytical range, the sample is often eluted from the guard column to the main column by means of a back-flash procedure. In micro and nanoLC, this is not usually done, since impurities held back at the head of the guard column are otherwise rinsed onto the main column, greatly increasing the risk of a blockage there. 

Highly flammable, bums with a purple-tinged flame vapor density 1.8 (air=l) the vapor may travel a considerable distance to an ignition source and flash back fireextinguishing procedure use a water spray... 

Flammable gas the gas (vapor) is heavier than air and can travel a considerable distance to a source of ignition and flash back autoignition temperature 402°C (755°F) fireextinguishing procedure shut off the flow of gas use dry chemical, CO2, or alcohol foam to extinguish fire involving its solution use a water spray for diluting and flushing the spill and to keep fire-exposed containers cool. 

Because it is used frequently to study photochemical reactions that lead to bond cleavage, this procedure is often called flash photolysis. The term photolysis literally means breaking apart by light," however, so technically it would not apply to the measurement of excited states that decay back to starting molecules without chemical change. 

Two of the most widely used methods for preparation of alpha sources on a metal backing for counting or spectroscopyare (1) direct evaporation of an aqueous or organic solution and (2) electrodeposition. Other methods, such as volatilization of the sample in a vacuum, adsorption from an aqueous solution, are not so widely used. However, the method of vacuum "flashing" from a tungsten filament produces very satisfactory sources and is in routine use in some laboratories. (See for example Procedure 4 in Sect. VUI.)... 

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