LaMotte DCL-20 Colorimeter - Manual (Page 12)

CALCIUM & MAGNESIUM TEST
SCHWARZENBACH EDTA METHOD
QUANTITY CONTENTS CODE
30 mL *Calcium & Magnesium Buffer *5126-G
60 mL Standard EDTA Reagent 5254-H
100 Calcium Hardness Indicator Tablets T-5250-J
30 mL Calcium Magnesium Inhibitor Reagent 3922-G
30 mL *CM Indicator Reagent *6522WT-G
30 mL *Sodium Hydroxide w/Metal Inhibitors *4259-G
15 mL *Inhibitor Solution *9258-E
15 mL *TEA Reagent *3921-E
2 Direct Reading Titrators, 0-1000 Range 0384
1 Pipet, transfer, plastic 0364
1 Test tube, 5-10-15 mL, glass, w/cap 0778
*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 MSDS before using.
The amount of total calcium in soils may range from as little as 0.1% to as much 25%. A calcium deficiency is rarely a
problem due to widely accepted practice of applying lime to soil to raise the pH to the proper range for optimum plant
growth. As an important mineral nutrient, calcium is a component of cell walls in plants and is known to stimulate root
and leaf development as well as activate several enzyme reactions involved in plant metabolism. Indirectly, calcium
influences crop yields by reducing soils acidity and by reducing the toxicity of several other soil minerals such as manganese,
zinc, and aluminum.
The Schwarzenbach EDTA titration method, used to determine calcium and magnesium, involves two titrations. The first
titration gives the calcium and magnesium content, the second only calcium. Magnesium is calculated from the difference
between the titration values.
Carefully read the LaMotte Direct Reading Titrator Manual before performing the titrations described below.
RANGE: Cal cium 0-400 lbs/A
Mag ne sium 0-240 lbs/A
METHOD: Ti tra tion with Schwarzenbach EDTA
IN TER FER ENCE: Sam ple color and tur bid ity may in ter fere with end point.
DILUTION OF SOIL EXTRACT
Use the 30 mL graduated cylinder (0418) to measure 10 mL of the soil extract and transfer it to a 50 mL beaker (0944).
Add 10 mL of deionized water, mix and neutralize according to the procedure on page 10.
TITRATION A, CALCIUM & MAGNESIUM
1. Fill the test tube (0778) to the 5 mL line with the soil extract from above. Dilute to the 10 mL line with deionized
water.
2. Add 5 drops of Calcium Magnesium Inhibitor Reagent (3922).
3. Wait 5 minutes.
4. Use a transfer pipet (0364) to add 5 drops of *Calcium & Magnesium Buffer (5126).
5. Add 10 drops of *CM Indicator (6522WT).
6. Fill the Direct Reading Titrator (0384) with the Standard EDTA Reagent (5254). Insert the tip of the Titrator into the
center hole of the test tube cap.
7. While gently swirling the tube, slowly press the plunger to titrate until the color changes from red to blue.
8. Read the Titrator scale at the tip of the plunger and multiply by 5.16. This is Titration Value A.
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1985-01 • 10/01