pH (25 C) X ml Y ml
5.8 4.0 46.0
6.0 6.15 43.75
6.2 9.25 40.75
6.4 13.25 36.75
6.6 18.75 31.25
6.8 24.5 25.5
7.0 30.5 19.5
7.2 36.0 14.0
7.4 40.5 9.5
7.6 43.5 6.5
7.8 45.75 4.25
8.0 47.35 2.65
Osmolarity is adjusted by varying the molarity of phosphates or by the addition of sucrose, glucose or sodium chloride.
At pH 7.2:
0.10M = 226 mOs (milliosmoles)
0.05M = 118 mOs
0.075 = 180 mOs
0.15M = 350 mOs
II. Cacodylate Buffer (arsenate buffer) pH 5-7.4
Advantages:
1. Easy to prepare.
2. Stable during storage for long periods of time.
3. Does not support growth of microorganisms.
4. Precipitates usually do not occur. Precipitates do not occur at low concentrations of calcium.
Disadvantages:
1. Toxic. Contains arsenic.
2. Unpleasant smell.
Preparation of Buffer:
Stock solutions:
0.2M sodium cacodylate 1 liter
Na(CH3)2As02*3H20 (MW = 195.92) 42.8 gm
+ ddH20 to make 1 liter
0.2M HC1
Conc. HC1 (36-38%) 10 ml
ddH20 603 ml
Working buffer: 0.1M 100 ml
Adjust 50 ml of 0.2M sodium cacodylate to desired pH with 0.2M HC1. Dilute to 100 ml with ddH20 or dilute 1:1 with fixative.
pH 0.2M HC1 (ml)
6.4 18.3
6.6 13.3
6.8 9.3
7.0 6.3
7.2 4.2
7.4 2.7
Buffer may also be made with cacodylic acid.
Stock solutions:
0.2M cacodylic acid 1 liter
(CH3)2AsO2H (MW = 138.0) 27.6 gm
+ ddH20 to make 1 liter
0.2M NaOH 100 ml
NaOH (MW = 40) 0.8 gm
+ ddH20 to make 100 ml
Working buffer: 0.1M
Adjust 50 ml of 0.2M cacodylic acid to desired pH with 0.2M NaOH. Dilute to 100 ml with ddH2 or dilute 1:1 with fixative.
III. Veronal-acetate Buffer (Michaelis buffer)
Advantages:
Useful for block staining with uranyl acetate since precipitates do not form.
Disadvantages:
1. Reacts with aldehydes.
2. Poor buffer at physiological pH.
3. Supports growth of micro-organisms.
4. Contains barbiturate.
Preparation of Buffer:
Stock solution: 0.28M 100 ml
Sodium veronal (barbitone sodium)
C8H1103N2Na (MW = 206.18) 2.89 gm
Sodium acetate (anhydrous)
CH3C00Na (MW = 82.03) 1.15 gm
or
Sodium acetate (hydrated)
CH3C00Na*3H20 (MW = 136.09) 1.90 gm
+ ddH2H20 to make 100 ml
Solution is stable and may be stored for some months at 4 C.
Worki