Oxygen, dissolved – LaMotte DC1600 Colorimeter User Manual

Page 63

OXYGEN, DISSOLVED

WINKLER COLORIMETRIC METHOD

CODE 3688

QUANTITY

CONTENTS

CODE

30 mL

*Manganese Sulfate Solution

*4167WT-G

30 mL

*Alkaline Potassium Iodide Azide

*7166WT-G

30 mL

*Sulfuric Acid 1:1

*6141WT-G

Sample Tube, screw cap

29180

Cap

28570

*WARNING: Reagents marked with a * are considered hazardous substances. Material Safety Data Sheets (MSDS) are supplied for

these reagents. For your safety, read label and accompanying MSDS before using.

Dissolved oxygen is vital to the survival of aquatic organisms. Naturally present, dissolved oxygen enters the water when

plant photosynthesize. Wind and wave action also cause oxygen from the air to dissolve into water. Dissolved oxygen is

consumed by aquatic animals and by the oxidation, or chemical breakdown, of dead and decaying plants and animals. The

concentration of dissolved oxygen in natural waters can range from 0 to 14 ppm and is effected by temperature and salinity.

APPLICATION:

This method is applicable for the determination of dissolve oxygen in drinking water, all

surface waters and wastewater.

RANGE:

0 – 12.5 ppm

METHOD:

This method use the azide modification of the Winkler Method with a colorimetric

determination of the yellow iodine produced from the reaction of the reagents with the

dissolved oxygen.

INTERFERENCES:

The presence of other oxidizing agents may cause positive interferences. Reducing may cause

negative interferences. Nitrite interferences are eliminated with the azide modification.

COLLECTION & TREATMENT OF THE WATER SAMPLE

Steps 1 through 4 below describe proper sampling technique in shallow water. For sample collection at depths beyond arm’s

reach, special water sampling apparatus is required (e.g. the LaMotte Water Sampling Chamber, Code 1060; Model JT-1

Water Samplers, Code 1077; Water Sampling Outfit, Code 3103; or Water Sampling Bottle, Code 3-0026).
1.

To avoid contamination, thoroughly rinse the screw cap Sample Tube with sample water.

Tightly cap Sample Tube and submerge to the desired depth. Remove cap and allow the Sample Tube to fill.

Tap the sides of the submerged bottle to dislodge any air bubbles clinging to the inside. Replace the cap while the

Sample Tube is still submerged.

Retrieve Sample Tube and examine it carefully to make sure that no air bubbles are trapped inside. Once a satisfactory

sample has been collected, proceed immediately with Steps 5 and 6 to “fix” the sample.
NOTE: Be careful not to introduce air into the sample while adding the reagents in steps 5 and 6. Simply drop the

reagents into the sample. Cap carefully, and mix gently.

Add 2 drops of *Manganese Sulfate Solution (4167WT) and 2 drops of *Alkaline Potassium Iodide Azide (7166WT).

Cap and mix by inverting several times. A precipitate will form. Allow the precipitate to settle below the shoulder of

the bottle before proceeding.

Add 2 drops of *Sulfuric Acid, 1:1 (6141WT). Cap and gently shake until the reagent and the precipitate have

dissolved. A clear-yellow to brown-orange color will develop, depending on the oxygen content of the sample.
NOTE: It is very important that all “brown flakes” are dissolved completely. If the water has a high DO level this

could take several minutes.
NOTE: Following the completion of step 6, contact between the water sample and the atmosphere will not affect the

test result. Once the sample has been “fixed” in this manner, it is not necessary to perform the actual test procedure

immediately. Thus, several samples can be collected and “fixed” in the field, and then carried back to a testing station

or laboratory where the test procedure is to be performed.