Heated water bath system

For heating reaction mixtures up to temperatures of 70 C, an electrically heated water bath seems most practical. For heating at higher temperatures, an oil bath (heated electrically or with a flame) is recommended. It should be pointed out, however, that any system whereby the reaction mixture is heated indirectly is not foolproof in the case of a threatening emergency situation (e.g. a sudden rise in temperature of the reaction mixture) the bath has to be removed, which may take several seconds. Although one may not be easily convinced, we can assure the reader that in many cases it is much better to heat the reaction flask with an open flame (cautiously moving the flame under the flask ). A water bath should always be at hand to neutralize a sudden rise in temperature. 

FIG. V-28 Electric heated vaporizer Circulating pumped water bath. System inciudes etectric immersion water heater, pump, piping, controls, and expansion tank, all factory piped up and delivered on skid ready to operate. (Source Armstrong Engineering Associates.)... 

Heat added to an ice-water mixture melts some of the ice, but the mixture remains at 0 °C. Similarly, when an ice-water mixture in a freezer loses heat to the surroundings, the energy comes from some liquid water freezing, but the mixture remains at 0 °C until all the water has frozen. This behavior can be used to hold a chemical system at a fixed temperature. A temperature of 100 °C can be maintained by a boiling water bath, and an ice bath holds a system at 0 °C. Lower temperatures can be achieved with other substances. Dry ice maintains a temperature of -78 °C a bath of liquid nitrogen has a constant temperature of-196 °C (77 K) and liquid helium, which boils at 4.2 K, is used for research requiring ultracold temperatures. 

Heat and reflux a 5-g portion of soil sample with 50 mL of methanol-phosphate buffer (pH 7)-water (15 7 28, v/v/v) solvent mixture in a round-bottom flask for 1 h. After cooling, transfer a 10-mL portion of the supernatant to a test-tube and mix with 11 mL of 0.02M H3PO4 solution. Load this solution on to a silica-based SPE cartridge (Analytichem International Clin-Elut 1020) at a flow rate of 1-2 drops per second. Discard this fraction. Elute the analytes with 30 mL of dichloromethane. Concentrate the eluate to dryness with air in a water-bath at a temperature of 40 °C (do not use vacuum). Dissolve the residues in 5mL of HPLC injection solution [900 mL of water - - 50 mL of phosphate buffer (pH 7) 4-50 mL of ACN 4-4 g of TBABr]. Pinal analysis is performed using liquid chromatography/ultraviolet detection (LC/UV) with a three-column switching system. 

A piece of metal weighing 500. grams is put into a boiling water bath. After 10 minutes, the metal is immediately placed in 250. grams of water at 40. °C. The maximum temperature that the system reaches is 50.°C. What is the specific heat of the metal (The specific heat of water is 1.00 cal/g °C.)... 

If good reproducibility of the retention times is required, the column temperature should be kept constant. A water bath or an air oven are common systems, and thermo-tape is also effective if the column is made of steel. When temperature control is extremely important, pre-heating of the eluent is necessary. If the whole apparatus is placed in a temperature-controlled box, the temperature is constant, but such a system is not usually required. 

The initial mixture and each time point are then assayed for doxorubicin and lipid. Lipid concentrations can be quantified by the phosphate assay (see above) or by liquid scintillation counting of an appropriate radiolabel. Doxorubicin is quantified by an absorbance assay (see below). The percent uptake at any time point (e.g., t = 30 minutes) is determined by %-uptake = [(D/L), =30minutes] x 100/[(D/L) inuiai]. Doxorubicin can be assayed by both a fluorescence assay and an absorbance assay, but we find the latter to be more accurate. The standard curve consists of four to five cuvettes containing 0 to 150 nmol doxorubicin in a volume of 0.1 mL samples to be assayed are of the same volume. To each tube is added 0.9 mL of 1% (v/v) Triton X-100 (in water) solution. For saturated lipid systems such as DSPC/Chol, the tubes should be heated in a boiling water bath for 10 to 15 seconds, until the detergent turns cloudy. Samples are allowed to cool, and absorbance is read at 480 nm on a UV/Visible spectrophotometer. 

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