Determination Of Phosphorus; Determination Of Potassium - MACHEREY-NAGEL VISOCOLOR Manual

Manual VISOCOLOR
ture. Weigh out 10 g of the air-dried, screened soil in a shaking
bottle (15). Add 200 mL of extraction solution B with the aid of the
measuring cylinder (8) and close shaking bottle. Shake bottle vig-
orously for 5 min, allow solid matter to settle briefly. Place plastic
funnel (7) in a 100 mL measuring cylinder (8), insert a folded filter
MN 616 ¼ (21). Filter suspension. If the solution is initially turbid,
pour it back into the folded filter. A slightly yellow inherent color of
soil extract B will not affect the following analysis.
ml 100
90
80
8
70
60
50
40
30
20
9
10
MN 616 ¼

2.10 Determination of phosphorus

Phosphorus analysis is carried out with a colorimetric test kit or
photometric under use of the kit VISOCOLOR
(see 3.7).
Procedure:
Place two measuring tubes (19) in the comparator block (20),
insert color disc. With the aid of the 1 mL plastic syringe (11)
transfer 1.6 mL of soil extract B into each of the measuring tubes
and fill to marking line with distilled water. Add 6 drops of P-1 (33)
to the right glass, mix. Add 6 drops of P-2 (34) to the right glass,
mix. Add 6 drops of P-K (35) to the left glass, mix.
P-1 P-2 P-K
33 34 35
26
®
reagent case for soil analysis
15 7
21
®
ECO Phosphate
20
19 11
After 10 min: look through the glasses from above, compare the
colors of the two glasses and turn the color disc until the colors
match. Read off the measurement value from the marking on the
front side of the comparator block. Intermediate values can be
estimated.
After use, rinse thoroughly and close. Do not use any rinsing
agent containing phosphate to clean the measuring tubes.
Calculation of results:
Read off result of phosphorus in mg/100 g P and multiply with
10 to receive the result in mg/kg P.
e.g. 6 mg/100 g P x 10 = 60 mg/kg P

2.11 Determination of potassium

Potassium is analyzed nephelometrically, i.e. the turbidity caused
by the potassium is measured. The turbidity measurement can
be done as described below visual or photometric (see 3.8)
Procedure:
Fill a clean sample tube for potassium (16) with soil extract B
up to the ring mark (16.8 mL). Add 15 drops of K-1 (37) to the
sample tube, close and mix. Add a flat measuring spoon (30) of
K-2 (38) to the sample tube, close and shake, not too vigorously,
for approx. 30 s (no reagent residues should be visible at the bot-
tom of the sample tube after shaking).
K-1 K-1
37
Pour the liquid from the sample tube into the potassium measur-
ing tube (25) until the black cross at the bottom of the measuring
tube becomes invisible (when looking into the tube from above).
Read the potassium content from the scale of the measuring
tube (meniscus bottom edge).
Calculation of results:
Read off result of potassium in mg/L K and multiply with 20 to
receive the result in mg/kg K.
e.g. 3 mg/L K x 20 = 60 mg/kg K
®
Manual VISOCOLOR reagent case for soil analysis 02.19
K-2
38 30 16
2
3
4
6
8
10
15
25
3 mg/L