With particles, like bacterial cells, the solution becomes patchy at low concentrations allowing actual ppm values to diverge from expected values. With molar concentrations, it is safe to assume that the solute is well mixed within the solution so that the concentrations change predictably with each dilution. Units like ppm are more common within microbiology when diluting bacterial cultures to low concentrations. Molarity is common for chemical applications. Serial dilution generally refers to selection preformed in the standard growth regimes typically used in the lab: flasks, test tubes, solid media, or 96-well plates. The concentration commonly reported in Molarity (M) or particles per ml (ppm). The illustration above follows the relationship between the A 1:10 dilution is also called a 10x dilution. The final volume of the diluted sample is 1000 µL (1 mL), and the concentration is 1/10 that of the original solution. Mixing 100 µL of a stock solution with 900 µL of water makes a 1:10 dilution. For a 1:100 dilution, one part of the solution is mixed with 99 parts new solvent. For example, a 1:10 dilution is a mixture of one part of a solution and nine parts fresh solvent. They are described as ratios of the initial and final concentrations. Serial dilutions are often performed in steps of 10 or 100. The initial concentration and target range needed determines the size and number of dilution steps required. Take 1 mL of this dilution and add to the next tube (10 -2. Aseptically add 1 mL of enrichment sample to the first tube (10 -1) and mix gently. Label tubes 10 -1 to 10 -10 indicating dilution factor. Doing this several times results in a range of concentrations. Using aseptic technique, dispense 9 mL of media into each of ten test tubes with sterile automatic dispenser or sterile 10 mL pipettes. The diluted sample is then used as the base solution to make an additional dilution. To perform a serial dilution, a small amount of a well-mixed solution is transferred into a new container, and additional water or other solvent * is added to dilute the original solution.
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