| |
WINKLER'S METHOD FOR THE DETERMINATION OF OXYGEN IN WATER
Determination is based on the oxidation of Mn(OH)2 by water oxygen. The reaction product is Mn(OH)4. Environmental pH in the sample should be alkaline. Then add acid and KI to the sample. The formed iodine is titrated sodium thiosulfate.
Interfering substances are the organic matters, nitrites, iron (2+ and 3+), reducing and oxidizing agents. Accuracy of definition is equal 0,5-1 % for concentration of oxygen more than 1 mg/L. The limit of method detection is 0,05 mg/L.
|
|
| |
PHOTOMETRIC DETEMINATION OF PHOSPHATE
Determination of phosphates bases on the creating of chemical compound with molybdenic heteropoly acids in acid environment. Water solution is not sufficiently intense color, so usually use reduced form of molybdenic heteropoly acid. This form is blue with bigger optical density. There are different reducing agents for molybdenic heteropoly acid such as ascorbic acid, sodium sulfite, stannum (II)chloride, hydroquinone. Most popular is stannum (II)chloride, because it gives the most intensive colouration.
|
|
| |
IONOMETRIC DETERMINATION OF FLUORIDE IN WATER
Behavior the electrode of fluoride (monocrystal of LaF3) is well investigated at present. Procedure of method became classical. Method is founded on use the masking reagent for cations Fe or Al. The citrate or ethylene diamine tetraacetate is this masking reagent.
Except masking reagent, solution must contains sodium chloride or potassium chloride for stabilization of ionic force. |
|
| |
IONOMETRY. METHOD OF CALIBRATION CURVE
Method of calibration curve is the simplest from ionometric methods of the analysis. Procedure of analysis contains 2 stages: calibration of the electrodes and measuring of samples.
Calibration consist in measuring of electric potential of ion-selective electrode (E) relative reference electrode in standart solutions. Measured data must be use for construction of graph. Graph's shape is straight line in the coordinates E of pX:
E = B - S pX,
where E is electric potential between ion-selective electrode and reference electrode;
S is slope of line;
B is constant. |
|
| |
IONOMETRY. TITRATION
The procedure of ionometric analysis is very typical for instrumental analysis methods. Pair of electrodes immerse in the sample. Then, to the sample adds a portions of titrant. After each portion of titrant write down ionomer indications. The titration curve is has s-shaped form in the coordinates E of V (see Fig. 1a). If solution contains a few sorts of ions, then curve titration can have a form with several inflection point. Each inflexion point is an equivalence point of the titration (see Fig. 1b). |
|
REFERENCE BOOK
|
|
