![]() However, concentrated stock solutions may precipitate when cooled and should be kept at room temperature until precipitate has completely dissolved before use. PBS can be stored at room temperature or in the refrigerator. Sterilization may not be necessary depending on its use. If used in cell culturing, the solution can be dispensed into aliquots and sterilized by autoclaving or filtration. PBS can also be prepared by using commercially made PBS buffer tablets or pouches. If necessary, pH can be adjusted using hydrochloric acid or sodium hydroxide. Where, is the density difference between the fluid and the sphere being investigated. The viscosity of a fluid can be determined by dropping a sphere into it and using the following formula: 2ga 2 ()/9v. When making buffer solutions, it is good practice to always measure the pH directly using a pH meter. The ratio of shearing stress to velocity gradient in a fluid is used to calculate viscosity. Add 2.84 mM of HCl to shift the buffer to 7.3 mM HPO 4 2− and 4.6 mM H 2PO 4 − for a final pH of 7.4 and a Cl − concentration of 142 mM. The resultant 1× PBS will have a final concentration of 157 mM Na +, 140mM Cl −, 4.45mM K +, 10.1 mM HPO 4 2−, 1.76 mM H 2PO 4 − and a pH of 7.96. Add distilled water to a total volume of 1 liter. Start with 800 mL of distilled water to dissolve all salts. Some formulations do not contain potassium and magnesium, while other ones contain calcium and/or magnesium (depending on whether or not the buffer is used on live or fixed tissue: the latter does not require CaCl 2 or MgCl 2 ). There are many different ways to prepare PBS solutions (one of them is Dulbecco's phosphate-buffered saline (DPBS), which has a different composition than that of standard PBS ). PBS has been shown to be an acceptable alternative to viral transport medium regarding transport and storage of RNA viruses, such as SARS-CoV-2. For these types of applications, Good's buffers are recommended. Divalent metals such as zinc, however, cannot be added as this will result in precipitation. PBS with EDTA is also used to disengage attached and clumped cells. These uses include substance dilution and cell container rinsing. PBS has many uses because it is isotonic and non-toxic to most cells. Measured values span several orders of magnitude. Viscosity is measured using a viscometer. F AV Y (2.6.1) (2.6.1) F A V Y V/Y also represents the velocity gradient (sometimes referred to as shear rate). For instance, honey has a much higher viscosity than water. The force necessary to move a plane of area A past another in a fluid is given by Equation 2.6.1 2.6.1 where V V is the velocity of the liquid, Y is the separation between planes, and is the dynamic viscosity. ![]() It corresponds roughly to the intuitive notion of a fluid's 'thickness'. The osmolarity and ion concentrations of the solutions match those of the human body ( isotonic). Dynamic viscosity is a material property which describes the resistance of a fluid to shearing flows. ![]() The buffer helps to maintain a constant pH. It is a water-based salt solution containing disodium hydrogen phosphate, sodium chloride and, in some formulations, potassium chloride and potassium dihydrogen phosphate. Phosphate-buffered saline ( PBS) is a buffer solution (pH ~ 7.4) commonly used in biological research. Buffer solution commonly used in biological research
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