INSTRUCTION MANUAL
CODE 80189 REV E
12/2020
Page: 52
J
.P. SELECTA s.a.u.
Autovía A-2 Km 585.1 Abrera 08630 (Barcelona) España
Tel 34 937 700 877 Fax 34 937 702 362
e-mail: [email protected] - website: http://www.jpselecta.es
7.3 Fixative solution checking and adjusting
Due to the differences existing between the water used for ammonia fixa
-
tive solution preparation (deionised, distilled from different assay,...) it is
necessary to check and adjust this solution to achieve a correct operation of
the equipment.
7.3.1. Material
•
Spectrophotometer suitable to work at 520 nm.
•
10 mm glass cuvette.
•
Flask with 0.01 ml resolution.
7.3.2 Using Boric acid solution 1% + 15 ml indicator:
(4.8 mixed, Metihyl red - Bromocresol green)
7.3.2.1
Checking:
•
Select 520 nm in the spectrophotometer.
•
Adjust blank with distilled water.
•
Measure the fixative solution absorbance value.
•
The value must be approximately around 0.650 (between 0.630 and
0.670).
7.3.2.2
Adjusting:
If the value is lower than 0.630:
Add HCl 0.1M till you get a value between 0.630 and 0.670 according to the
following formula: V = (0.650 - L) x 1515
where:
V = HCl 0.1M volume to be added per dissolution litre (ul).
L = Solution absorbance at 520 nm.
If the value is higher than 0.670:
Add NaOH 0.1M till you get a value between 0.630 and 0.670 according to
the following formula: V = (L- 0.650) x 1515
where:
V = NaOH 0.1M volume to be added per dissolution litre (ul).
L = Solution absorbance at 520 nm.
Note:
•
These formulas are orientative. Add a lower quantity than calculated one,
and check again the result.
•
The expression “ul” should be read as “microlitre”.
7.3.2.3 Example:
We have a solution whose absorbance (at 520nm) is:
L = 0.559
•
According to 7.3.2.2, we have to add:
V = (
0.650
-
0.559
) x
1515
ul =
137.86
ul
(of HCl 0.1 M per solution litre)
•
Instead of adding
137.86
ul, we add
100
ul of HCl 0.1 M.
•
We repeat the reading.
•
The new reading is: L =
0.611
•
We add 50 ul more and repeat the reading L =
0.640
•
Now we have the solution prepared to work.
