Hotplate

Let s just suppose, hypothetically, that the underground chemist is too stupid or unwilling to get a stir plate. In this case a single unit portable hotplate can work, but controlled heat using these is best accomplished by water or oil baths. Stirring can be accomplished by attaching a shaft and paddle to a power drill or any gear driven motor. 

Emetine andcephaeline, the two major alkaloids of ipecacuanha, begin to fluoresce after treatment with iodine vapor [254], The molecular iodine, which acts as a quencher, must be removed by heating in the drying cupboard or on a hotplate... 

TLC plate which is wetted with reagent solution when it leaves the dipping bath before laying it on the hotplate, laboratory bench or scanning stage. 

Since it still is not a simple matter to heat a TLC plate really homogeneously there is a danger of reaction inhomogeneities on the plate. The usual types of apparatus employed for heat production and transfer are drying cupboards, hotplates and IR sources. The success obtained using microwaves has been modest up to now. 

Hotplates (Fig. 45) are coming into increasing use for heating chromatograms. They have the advantage that it is possible to follow the reaction visually and the... 

At low temperatures the average temperatures ealeulated from the individual measurements eorresponded to the temperature setting. They were appreeiably lower at higher temperatures and it was found that the temperature setting eorresponded to the highest temperature that eould be reaehed in the individual measurements. It was also evident that the edge of the hotplate was eolder than the middle, i.e. the effeetive measured temperature was not the same everywhere over the surface of the hotplate a homogeneous temperature distribution is most likely to be found in the center of the plate. 

Detection and result The chromatogram was freed from mobile phase, immersed for 1 s in the dipping reagent and then heated on a hotplate at 100°C for 5 min. 

Regulations 1964 Economisers, Superheaters, Steam Tube Ovens and Steam Tube Hotplates... 

Thermal shock resistance is important for gas cooker pan supports and hotplates where spillage is liable to occur, but in oven interiors heat resistance is more relevant. 

Procedure. Allow the whole of the sample solution (1 L) to flow through the resin column at a rate not exceeding 5 mL min . Wash the column with 250 mL of de-ionised water and reject the washings. Elute the copper(II) ions with 30 mL of 2M nitric acid, place the eluate in a small conical flask (lOOmL, preferably silica) and evaporate carefully to dryness on a hotplate (use a low temperature setting). Dissolve the residue in 1 mL of 0.1 M nitric acid introduced by pipette and then add 9 mL of acetone. Determine copper in the resulting solution using an atomic absorption spectrophotometer which has been calibrated using the standard copper(II) solutions. 

The essential requirements for a constant-current electrolytic determination — a source of direct current (which may be a mains-operated unit producing a rectified smoothed output of 3-15 volts), a variable resistance, an ammeter (reading up to 10 amperes), a voltmeter (10-15 volts), and a pair of platinum electrodes — can be readily assembled in most laboratories, but if a number of determinations are to be performed a commercial electrolysis unit will doubtless be preferred. This will be equipped with rectifier, a motor drive for a paddle-type stirrer or with a magnetic stirrer, and a hotplate. 

Detection and result The chromatogram was freed from mobile phase and placed in an atmosphere of chlorine gas (twin-trough chamber, containing 20 ml solution I in the second chamber) for 1 min. Then the excess chlorine was removed (30 min stream of warm air), the treated chromatogram immersed in the dipping solution for 3 s and dried on a hotplate (60-70 °C). 

Heterocyclics 252, 260, 299,416 n-Hexadecanol esters 63 Hexaporphyrin 102 Hexitols 426 Hexobarbital 254,255 Hexoses 161,202 Hexuronic acid 158 Histamine 294,296, 355 Homogentisic acid 166,167 Horizontal chamber 127 Hotplates 93 ff -, temperature distribution 95 Hydrazines 269,284 Hydrazone formation 71 ff -with 2,4-dinitrophenylhydrazine 71, 72, 274... 

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