Glassware precautions

Three important precautions are needed when working with pipets and volumetric flasks. First, the volume delivered by a pipet or contained by a volumetric flask assumes that the glassware is clean. Dirt and grease on the inner glass surface prevents liquids from draining evenly, leaving droplets of the liquid on the container s walls. For a pipet this means that the delivered volume is less than the calibrated volume, whereas drops of liquid above the calibration mark mean that a volumetric flask contains more than its calibrated volume. Commercially available cleaning solutions can be used to clean pipets and volumetric flasks. 

Acetone can be handled safely if common sense precautions are taken. It should be used in a weU-ventilated area, and because of its low flash point, ignition sources should be absent. Flame will travel from an ignition source along vapor flows on floors or bench tops to the point of use. Sinks should be rinsed with water while acetone is being used to clean glassware, to prevent the accumulation of vapors. If prolonged or repeated skin contact with acetone could occur, impermeable protective equipment such as gloves and aprons should be worn. 

Practical experience enables us to emphasize the simplicity and the efficiency of the activation of aldehydes by their conversion into N- -haloalkyl)heteroarylium halides upon treatment with an azine and a thionyl halide. Preparation of these salts requires a minimum of precautions, and a wide variety of solvents can be used. Special glassware and/or the use of an inert gas is not necessary. Tire salts can be reacted under numerous experimental conditions and, in most cases, it is unnecessary to isolate them. Tire flexibility of the method represents an interesting feature for the study of the reactivity of A-(l-haloalkyl)heteroarylium halides and deserves further investigations in this held. Many elegant compromises can be found in a judicious choice of the precursors and of the experimental conditions, and it is possible to design readily a salt suitable for each individual purpose. 

Precautions. Prepared materials were treated with techniques used for radioactive or infectious material. The work was performed in an isolated laboratory. Glassware and tools were segregated. The hood was... 

The receiver was cooled to -78°C and a small amount of triethylamine was added to the cold solution to stabilize the product against acid-catalyzed polymerization. As an added precaution, all glassware was base-washed prior to use. 

The ETHOS MR is constituted of a multimode cavity very close to domestic oven with safety precautions. It can use standard glassware or glass (420 mL up to 2.5 bar) and polymer reactors (375 mL up to 200 °C and 30 bar) with magnetic stirring. The magnitude of microwave power available is 1 kW. The optical temperature sensor is immersed in the reaction vessel for quick response up to 250 °C. An infrared sensor is also available. A ceiling mounted is available in order to make connection with a conventional reflux system located outside the cavity or to ensure addition of reactants. 

Chlorine at the percentage level at which it occurs in sea water is usually determined by classical procedures using standard silver nitrate as the titrant and potassium chromate indicator, or alternatively by the mercuric thiocyanate procedure using dithizone as indicator. As large dilutions of the original sample are involved in these analyses, it is essential to use grade A glassware and take all other suitable precautions, such as temperature control. 

Because of the ubiquitous nature of FMs in consumer products, it is critical that any analytical chemistry laboratory measuring these compounds takes extra precautions to avoid laboratory contamination of samples. Several researchers [2,11,14-17] have pointed out that likely sources of FM contamination in the modern-day laboratory include the use of consumer products and fine fragrances by laboratory workers, fragrances in soaps used to clean glassware and the laboratory, and laboratory supplies such as gloves. 

Precautions were taken whilst azeotroping the catalyst with toluene thus the use of freshly dried toluene and flame-dried glassware were necessary to ensure anhydrous conditions. 

Heating a flask. Since they are cold-blooded creatures, flasks show more of their unusual behavior while being heated. The behavior is usually unpleasant if certain precautions are not taken. In addition to star cracks, various states of disrepair can occur, leaving you with a benchtop to clean. Both humane and cruel heat treatment of flasks will be covered in (see Chapter 13, Sources of Heat ), which is on the SPCG (Society for the Prevention of Cruelty to Glassware) recommended readings list. 

Precautions should be taken when selecting various vessels of differing materials for the extraction of these steroids from their matrices. For example, the compatibility of some solvents with plastic extraction tubes may present some problems. If glass vessels are to be selected, it is recommended that all glassware is silanized prior to use since several steroids bind to glass surfaces. 

Scrupulous cleanliness is an absolute must in working with monolayers [104] all materials used should be of the highest purity solvents and solutions should be dust-free glassware should be cleaned with a special cleaning solution and kept separate from other equipment the film balance should be kept in a clean area on a vibration-free table and surgical gloves should be worn at all times. These necessary precautions have been elaborated in frightening detail in a recent publication [114] and a review [107]. 

To reduce the source of bias, it is important to have an authentic reliable reference standard, a properly maintained and calibrated balance, knowledge of the purity and form of the standard, calibrated glassware, calibrated pipettes, analyte-free matrix, and pooled and individual lots. Poor calibration, incorrectly or poorly prepared standards, interaction between analytes and container, and incomplete reactions will lead to bias. Some further precautions can be taken to minimize the possibility of errors, such as preparing QC samples in bulk (pools) and separately from the calibrators, which are prepared fresh everyday. 

CAUTTON Diazomethane is highly toxic and irritating. It is also a detonator and appropriate safety precautions and procedures should be used when handling this reagent (e.g., special glassware, blast shield,... 

Note For all preparations In this section, glassware most be thoroughly clean and dir reagents must be of the highest purity available. These precautions are absolutely necessary to ensure highest yields. 

All optical rotations were measured at the D-line of sodium with a Perkin-Elmer polarimeter (model 141) using a thermostatted 10-cm polarimeter tube dried by a stream of filtered, dried air. Precaution was necessary to exclude water from the solutions in 1,2-dichloroethane and dimethyl sulfoxide. In this connection all glassware was dried at 120 °C and stoppered while hot. All transfers of solvents or solutions were made with syringes using serum caps to exclude moist atmosphere. The compounds which could not be prepared in crystalline condition and recrystallized to purity were obtained from a pure crystalline derivative... 

Disposable glassware may also be cleaned as a precaution against contamination. An alternate cleaning procedure based on saponification of fat adhering to the glassware is described in AOCS Method Cd I2b 92. 

All glassware should be thoroughly cleaned and siliconized. If these precautions are not taken, the gold spheres will adhere to the side vessel walls, which is evidenced by a red coloration of the glass. 

On completion of the reaction, the material may be carefully degassed to remove any entrapped gasses and unreacted diisocyanate. Care must be taken to prevent foaming. Applying vacuum to the glassware does create the potential for it to implode. Suitable safety precautions must be taken. Table 3.2 indicates some typical time/temperature reaction conditions for some simple prepolymers. 

A clean laboratory and equipment are undoubtedly crucial to all analytical methods. For trace element and POP measurements, however, additional precautions need to be taken. Glassware and other materials used for storing samples may act as both a source and a sink for some transition and heavy metal ions. Consequently, it is important to clean glassware and polyethylene equipment several times with dilute solutions of nitric acid followed by deionized water. Gloves must be worn whenever working with samples and sampling equipment. 

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