Preparation and Standardization of the Solutions.
EDTA solutions (0.05 M) were standardized with a standard
zinc solution, with xylenol orange as indicator, and the concentration
of a 0.01 M stock solution of DTPA was determined by
titration with a standard lead solution, with xylenol orange as
indicator (11). The DTPA solution was made in 0.1 M KNO3 in
order maintain a constant ionic strength in the titration
solutions. Stock solutions of mercuric nitrate and mercuric
chloride (0.05 M) were prepared in distilled, deionized water.
It was necessary to add a small amount of concentrated nitric
acid to completely dissolve the mercuric nitrate. These solutions
were standardized either directly with EDTA, or by backtitration
of excess EDTA with a standard zinc solution, with
xylenol orange as indicator (11). The excess acid in the mercuric
nitrate solution was determined by adding a known amount of
EDTA that was equimolar or slightly in excess of the mercury
concentration, and then performing a potentiometric titration
with a solution of standard base (12). Glutathione stock
solutions that were approximately 0.05 M were made daily in
freshly boiled, distilled deionized water, from which oxygen was
removed by bubbling nitrogen through the solution. Approximately
0.1 mmol of the ligand was titrated with standard
base, and the program PKAS (13, 14) was used to determine
the concentration of the ligand, as well as the acid dissociation
constants of the ligand. Standard HCl (0.1000 M) was added
to the titration vessel to adjust the initial pH to approximately
2.8. A 50% w/v stock solution of potassium hydroxide was made
in freshly boiled distilled deionized water and filtered through
a GF/A glass fiber filter purchased from Gelman (Ann Arbor,
MI). This solution was used to prepare a 0.1 M KOH solution
in freshly boiled, distilled deionized water which had been cooled
under nitrogen. The base solution was kept under nitrogen in
the reservoir of a 5 mL buret and was standardized against
potassium hydrogen iodate with methyl red as indicator. Solutions
of 0.1 M KCl and 0.1 M KNO3 were made in freshly boiled,
distilled deionized water.
Preparation and Standardization of the Solutions.
EDTA solutions (0.05 M) were standardized with a standard
zinc solution, with xylenol orange as indicator, and the concentration
of a 0.01 M stock solution of DTPA was determined by
titration with a standard lead solution, with xylenol orange as
indicator (11). The DTPA solution was made in 0.1 M KNO3 in
order maintain a constant ionic strength in the titration
solutions. Stock solutions of mercuric nitrate and mercuric
chloride (0.05 M) were prepared in distilled, deionized water.
It was necessary to add a small amount of concentrated nitric
acid to completely dissolve the mercuric nitrate. These solutions
were standardized either directly with EDTA, or by backtitration
of excess EDTA with a standard zinc solution, with
xylenol orange as indicator (11). The excess acid in the mercuric
nitrate solution was determined by adding a known amount of
EDTA that was equimolar or slightly in excess of the mercury
concentration, and then performing a potentiometric titration
with a solution of standard base (12). Glutathione stock
solutions that were approximately 0.05 M were made daily in
freshly boiled, distilled deionized water, from which oxygen was
removed by bubbling nitrogen through the solution. Approximately
0.1 mmol of the ligand was titrated with standard
base, and the program PKAS (13, 14) was used to determine
the concentration of the ligand, as well as the acid dissociation
constants of the ligand. Standard HCl (0.1000 M) was added
to the titration vessel to adjust the initial pH to approximately
2.8. A 50% w/v stock solution of potassium hydroxide was made
in freshly boiled distilled deionized water and filtered through
a GF/A glass fiber filter purchased from Gelman (Ann Arbor,
MI). This solution was used to prepare a 0.1 M KOH solution
in freshly boiled, distilled deionized water which had been cooled
under nitrogen. The base solution was kept under nitrogen in
the reservoir of a 5 mL buret and was standardized against
potassium hydrogen iodate with methyl red as indicator. Solutions
of 0.1 M KCl and 0.1 M KNO3 were made in freshly boiled,
distilled deionized water.
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