Ideally the pH should not change much between 10X and 1X if deionised water was used for dilution. Presnce of NaCl has nothing to do with pH changes since it contributes neither hydroxyl nor hydrogen ions (unless otherwise it is contaminated with something else), the balance of which determines pH (not just ionic strength). The balance between the monobasic and dibasic is thus maintained the same whatever dilution the stock is diluted to. If stock concentrations affected pH, many companies that make 10X buffer stocks will be out of business. During dilutions make sure to use deionised water (Millipore MilliQ for example) or the ions in water can slightly affect the pH, but not that significantly as you observed. Jay
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of DK Sent: Tuesday, January 03, 2012 6:08 PM To: [email protected] Subject: Re: 10X PBS In article <[email protected]>, sudheer sangeetham <[email protected]> wrote: >Hi People > >I have few doubts regarding phosphte buffer saline (PBS). Recently I found >one article related to my work, in that they used PBS ( Nacl/iP ) pH-7.4. >Nacl/iP does it mean, it should contain Na2HP04 and NaH2PO4 and Nacl but >not KCl, am I right? > >I have prepared the buffer like this > >NaH2PO4 ( 0.038M) >Na2HPO4.2H20 ( 0.162M) >NaCl (1.5 M ) but when i check the pH it was showing 6.4, is it correct? >did I do any mistake.... 1. Measurng pH in ~ 2 M NaCl is not going to be very meaningful with most electrodes. 2. pKa is a function of ionic strenght - no surprise that 10X and 1X have different pH. 3. Dilute 10X, measure pH and if it's not above 7.2, you either made an error making the solution or pH electrode is not measuring correctly. 4. The ratio you used above is for 0.2 M sodium phosphate, another 10X away from your 20 mM. (The difference between 200 and 20 will be small but not negligible). 5. "PBS" can stand for many things. Cell culture PBS solutions contain not ony some KCl (around 10 mM) but also some divalents, CaCl2 and/or MgCl2. DK _______________________________________________ Methods mailing list [email protected] http://www.bio.net/biomail/listinfo/methods This email message may contain legally privileged and/or confidential information. If you are not the intended recipient(s), or the employee or agent responsible for the delivery of this message to the intended recipient(s), you are hereby notified that any disclosure, copying, distribution, or use of this email message is prohibited. If you have received this message in error, please notify the sender immediately by e-mail and delete this email message from your computer. Thank you. _______________________________________________ Methods mailing list [email protected] http://www.bio.net/biomail/listinfo/methods
