Common Methods and Technical Guidelines for Preparing Solutions in the Laboratory
I. Principles of Preparing Common Stock Solutions and Buffer Solutions
In molecular biology and biochemistry experiments, accurately preparing various solutions is fundamental to experimental success. This section will detail the preparation methods, precautions, and application principles of commonly used stock solutions in laboratories.
Preparation of Spermidine and Spermine Solutions
Spermidine (spermidine) and spermine (spermine) are polyamine compounds often used as cationic polymers in DNA-related experiments to neutralize the negative charge of DNA, facilitating its binding with cell membranes. To prepare a 1 mol/L spermidine solution, accurately weigh 2.55 g of spermidine powder, dissolve it in an appropriate amount of ultrapure water, and finally dilute to 10 ml. Since spermidine is prone to oxidation degradation, it is recommended to aliquot the prepared solution into small portions of 500 μl each and store them at -20°C to avoid repeated freeze-thaw cycles.
The preparation method for spermine solution is similar but differs due to its molecular weight. To prepare a 1 mol/L spermine solution requires weighing out 3.48 g of spermine powder similarly dissolved up to 10 ml. These two polyamine solutions play important roles in DNA transfection experiments by significantly improving transfection efficiency. It should be noted that these two solutions may exhibit cytotoxicity at high concentrations; therefore, their usage concentration needs optimization based on experimental systems.
Preparation and Application of Ammonium Acetate Buffer Solution
A common high-salt buffer used in nucleic acid precipitation experiments is a 10 mol/L ammonium acetate (ammonium acetate). When preparing this buffer solution, weigh out 77.1 g of ammonium acetate powder; dissolve it in approximately 800 ml ultrapure water while stirring magnetically until completely dissolved before diluting it up to a final volume of 1 L. Due to microbial growth potential from high-concentration salt solutions, it’s advisable to filter sterilize using a membrane filter with a pore size of 0.22 μm.
Ammonium acetate buffer has multiple applications within molecular biology: first off during ethanol precipitation where ammonium acetate can replace sodium chloride more effectively precipitating small fragment DNAs; secondly during RNA extraction processes where ammonium acetate selectively precipitates RNA while leaving DNA soluble; additionally it's frequently utilized during plasmid DNA purification steps as well as noting that when stored at temperatures around +4°C crystallization may occur thus requiring warming prior use through water bath heating at +37°C until fully dissolved again.
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VI Special Reagent Handling Methods
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