Microwave oven checking

A mixture of appropriate indole-2,3-dione 1 (2 mmol) and 2-pyrrolidone 2 (5 mmol) was introduced in a microwave oven and irradiated at 840 W till the completion of the reaction. Progress of the reaction was checked by TLC. Extraction with acetic acid and removal of the solvent afforded the product which was analyzed by 1H NMR and found to be of sufficient purity on TLC. 

The pressure cooker-microwave heating method is simpler than the autoclave procedure and more efficient than microwave heating alone. The pressure cooker does not require checking the level of the antigen retrieval solution during heating in the microwave oven, and a large number of slides can be loaded simultaneously. In addition, the pressure... 

A slice 5 mm thick is cut from fixed brain tissue and washed for several hours in distilled water to remove excess formaldehyde. The slice is immersed overnight in Tris-buffered saline (TBS, pH 9.0) and then placed in a plastic jar containing 200 ml of TBS. The jar is placed in a microwave oven for 10-15 min at full power (700 W), divided into two cycles of 5 or 7.5 min to check the fluid level. The temperature is controlled using the temperature probe of the oven. It takes 3 min to reach a temperature of 90°C. 

After being washed in three changes of 5 min each in PBS, the slide is placed in a plastic jar containing 60ml of 10 mM sodium citrate buffer (pH 6.0) and 0.04% Triton X-100. The jar is loosely covered with its screw cap and heated for 5 min in a microwave oven at high power. The buffer starts to boil after 90 sec. The heating process is interrupted at intervals of 1 min so that the fluid level can be checked and replenished in the jar. The sections must not be allowed to dry. The jar is removed from the oven and allowed to cool to room temperature for 20-30 min. The sections are rinsed in three changes of 5 min each in PBS. 

Tissue specimens are fixed with 4% formalin for 24hr and embedded in paraffin. Sections (4 xm thick) are mounted on poly-L-lysine-coated slides, deparaffmized in xylene, rehydrated in a descending series of ethanol, and dried for lhr at 60°C. Endogenous peroxidase activity is blocked with 1% H202 in methanol for 15 min. The slides are placed in a plastic jar filled with 0.01 M sodium citrate buffer (pH 6.0), which is placed in a microwave oven. They are treated at 750 W for three periods of 5 min each. During each heating cycle the buffer level is checked, and the evaporated portion is replaced with distilled water. 

The determination of water content of soil by microwave oven has been standardized by the ASTM D4643. This test is not intended as a replacement for ASTM D2216 (mechanical convection oven method) but, rather as a supplement when more rapid results are required or desired to expedite other phases of testing. ASTM D2216 (mechanical convention oven method) is used to compare with for accuracy checks and correction. 

Microwave ovens can be hazardous if misused or not properly maintained. The federal leakage standard for microwave ovens is a power density of 5 milliwatts per cm, measured at a distance of 5 centimeters from the surface of the oven. Inexpensive microwave leak detectors are commercially available one should be obtained for any laboratory using microwave ovens to periodically check for radiation leakage. Also, the mechanical integrity of the door and seals and viewing screen should be checked at least once annually. 

Tensmeyer et al. (1981) developed a sterihzation method for empty glass containers, using a laser and a microwave oven. Sterihzation procedures were evaluated at power levels upto 2000 Watts. It was observed that spore destruction was logarithmically related to the exposure time. B. subtilis spores were used to check the efficiency. All the spores got destroyed with no particulate contamination being introduced into the glass containers. 

Areas of high microwave flux are checked with a Pelco 36140 microwave bulb array (Ted Pella). Specimens are not placed in areas indicated by illuminated bulbs. Vials containing the specimens are placed in a cold tap water bath (50 ml) that is preheated to the required temperature. The temperature is regulated by placing the microwave temperature probe into a vial of the same solution that is present in the specimen vial. The built-in temperature probe displays the specimen temperature on the oven front panel. The wire that attaches the probe to the oven is submerged in the water to decrease the antenna effect. An additional 400 ml of static water load is placed in the oven at an optimal position determined with the microwave bulb array. This water is changed between every step. 

Microwave analysis of moisture is also known as LOD (loss on drying), drying test, or total volatile solids. For many years, the standard oven test was used for moisture determination. Although very accurate, the test could take many hours to complete, depending on the sample. The time lapse rendered it practically useless for anything except a final quality control check. The new microwave moisture/solids analyzers were introduced about 20 years ago. They offer rapid, accurate moisture/solids analysis in a fraction of the time it took to run a standard oven-drying test. 

---