m***z
发帖数: 166 | 1 【 以下文字转载自 Biology 讨论区 】
发信人: mengz (雕刻时光), 信区: Biology
标 题: 0.1 M carbonate/bicarbonate buffer (pH 8.5)怎么配
发信站: BBS 未名空间站 (Mon Mar 12 21:35:08 2007)
多谢 google不到。 | R*j
发帖数: 248 | 2 先选缓冲对：NaHCO3 和 Na2CO3；HCO3- 的PKa是10.25;
设 NaHCO3 和 Na2CO3 的终浓度为 A 和 B;
列两个方程：
8.5 = 10.25 + log(B/A) -------------> H-H equation
0.1 = A + B
剩下该怎末办就不用再说了吧。要QS的时候用其他酸碱微调pH倒8.5
虽说你是生物专业，这点化学基础也要有吧？不过也难怪，美国实验室都买buffer.没
人配了。 | r****x
发帖数: 1250 | 3 preparing buffer based on an equation is a theoretical way, but 95% of the
time you won't get the pH right and will have to adj the pH at the end.
one practical way, might be kind of complicated for the first time, could
get exact pH (+/-0.05) easily, as long as your pH meter is calibrated right
every time.
Example:
0.1 M Na2CO3 and 0.1 M NaHCO3, 500 mL each
measure pH of each
take 100 mL of either one (preferably the one with pH closer to your target)
start titrating with the other one, to the
【在 R*j 的大作中提到】
: 先选缓冲对：NaHCO3 和 Na2CO3；HCO3- 的PKa是10.25;
: 设 NaHCO3 和 Na2CO3 的终浓度为 A 和 B;
: 列两个方程：
: 8.5 = 10.25 + log(B/A) -------------> H-H equation
: 0.1 = A + B
: 剩下该怎末办就不用再说了吧。要QS的时候用其他酸碱微调pH倒8.5
: 虽说你是生物专业，这点化学基础也要有吧？不过也难怪，美国实验室都买buffer.没
: 人配了。
| s******r
发帖数: 75 | 4 What about 0.1 M Ammonium bicarbonate? How to prepare it if no Ammonium
bicarbonate available?
right
target)
【在 r****x 的大作中提到】
: preparing buffer based on an equation is a theoretical way, but 95% of the
: time you won't get the pH right and will have to adj the pH at the end.
: one practical way, might be kind of complicated for the first time, could
: get exact pH (+/-0.05) easily, as long as your pH meter is calibrated right
: every time.
: Example:
: 0.1 M Na2CO3 and 0.1 M NaHCO3, 500 mL each
: measure pH of each
: take 100 mL of either one (preferably the one with pH closer to your target)
: start titrating with the other one, to the
| R*j
发帖数: 248 | 5 Good point. Yes, I agree that titration is the very practical method, and is
widely used in the lab. Yet, if you prepare a specific buffer for the first
time, calculation using H-H equation can at least give you some sense on
the ratio of buffer pair. When you pour one solution to the other, you
roughly know how much is needed.
【在 r****x 的大作中提到】
: preparing buffer based on an equation is a theoretical way, but 95% of the
: time you won't get the pH right and will have to adj the pH at the end.
: one practical way, might be kind of complicated for the first time, could
: get exact pH (+/-0.05) easily, as long as your pH meter is calibrated right
: every time.
: Example:
: 0.1 M Na2CO3 and 0.1 M NaHCO3, 500 mL each
: measure pH of each
: take 100 mL of either one (preferably the one with pH closer to your target)
: start titrating with the other one, to the
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