Stopping reagents

Preparation of low-molecular-weight polysilalkylenes can be by the use of stop reagents. Figure 2 shows the relationship between polydimethylsiltrimethylenes q and quantity of a stop reagent (here -hexylalkohol) added to the starting monomer. 

Stop the reaction by adding stop reagent (50 pl/well) and measure the absorbance using a microplate reader. 

They should be checked regularly for precision and accuracy of delivery volumes. Instructions on how to do this are usually included with the pipets If not, ask the manufaeturer how they are to be checked. Limited maintenance of the pipets should be made with attention to the plimgers in multichannel pipets, which get contaminated. Care should be taken to make sure that liquids are not pulled into the pipet if so, they must be cleaned. Corrosion ean occur when, e.g., sulfuric acid stopping reagent is taken into the body of a pipet. 

Asa stopping reagent—to stop enzyniatic reaction. fl points)... 

The OPA derivatization reaction is rapid at room temperature, but, as with most chemical reactions, the time to completion can be long. This means that the derivatization reaction must be stopped at a carefidly controlled time to get repeat-able, accurate results. The reaction can be stopped either by injecting the sample onto the column or adding a stopping reagent to the reaction. Either of these means is apphcable to autosampler automation (Carpino and Han, 1972). 

Note 4. At lower temperatures part of the reagent may crystallize out and the reaction becomes very slow or even stops. 

Vigorous oxidation leads to the formation of a carboxylic acid but a number of meth ods permit us to stop the oxidation at the intermediate aldehyde stage The reagents most commonly used for oxidizing alcohols are based on high oxidation state transition met als particularly chromium(VI)... 

Onc-Factor-at-a-Timc Optimization One approach to optimizing the quantitative method for vanadium described earlier is to select initial concentrations for ITiOz and 1T2S04 and measure the absorbance. We then increase or decrease the concentration of one reagent in steps, while the second reagent s concentration remains constant, until the absorbance decreases in value. The concentration of the second reagent is then adjusted until a decrease in absorbance is again observed. This process can be stopped after one cycle or repeated until the absorbance reaches a maximum value or exceeds an acceptable threshold value. 

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