MANUAL DE INSTRUCCIONES
CODIGO 80189 REV E
12/2020
Pag.: 55
J
.P. SELECTA s.a.u.
Autovía A-2 Km 585.1 Abrera 08630 (Barcelona) España
Tel 34 937 700 877 Fax 34 937 702 362
e-mail: [email protected] - website: http://www.jpselecta.es
8.1.9 Collector contaminated
The titration will be wrong if at the beginning of the analysis the collector has any
drop of HCl.
The titration will be also wrong if at the beginning of the analysis the collector has
any drop of distilled from previous sample not neutralized by titration.
The equipment detects this situation by indicating: “Low/High Signal Level”, which is
normally solved by cleaning the collector.
So you must be sure the collector is clean before any analysis, see 8.1.7.
Normally, a cleaning operation must be run after running operations 8.1.3 and 8.1.5.
The volume consumption of HCl (Vol
-
HCl
) on the titration can be forecasted
from the expression:
P
1
(mg) = 14 x Vol
HCl
(ml)
x N
HCl
thus we obtain that HCl must be:
Vol
HCl
(ml) = 14 /[ P
1
(mg) x N
HCl
]
8.3 Blank test
This checking must be run on each batch in order to quantify the absence of am
-
monia on the reagents.
It consists on distilling and titrating a sample of 25ml distilled water.
Add 15ml of NaOH on the distillation.
Run some blank tests in order to get a constant value of blank. If this value is
repeated, it could be subtracted from the detected Nitrogen.
8.2 Checking Nitrogen Recovery.
This checking is widely used to certify that the unit works properly.
Run some of these tests for training purposes, before starting to analyse valuable
samples, until the operator will be familiar with the unit.
It consists on preparing some samples that have a known Nitrogen content. It is
distilled, titrated and the nitrogen detected is calculated.
The rate (%) of nitrogen detected versus the sample Nitrogen content gives us the
Nitrogen Recovery
.
To allow this checking, a 100gr ammonia sulphate flask is delivered together with
the distiller.
• Weight near 100mg (50mg reagent 0.1N) of ammonia sulphate. The exact
weight will be P
0
• The exact quantity of Nitrogen is: P
1
(mg) = P
0
x 0,212
• Add around 25ml of H
2
O
• Distillate adding 15ml of NaOH
• Use HCl 0.25N (0.1N) as a titration reagent.
• Once distillation and titration are finished, the PRO-NITRO «A» gives the de
-
tected nitrogen (mg): P
2
• The recovery is calculated:
R(%) = P
2
/ P
1
*100
• Acceptable values are from 99.0 to 101%.
Note:
Some literature sets that the acceptable values for recovery must be above
99.5%. To get this result you must work with high precision and use reagents with
high purity degree.
How many ammonia sulphate
must I use on the test sample?
The HCl volume (Vol
HCl
) for a quick
analisys must be between 6 and 12
ml.
From the expresion:
P
1
(mg) = 14 x Vol
HCl
(ml)
x N
HCl
We arrange it as:
P
0
(mg) =
14 x Vol
HCl
(ml) x N
HCl
0.212
And get the table:
Normality
Sample amount
suphate amm.
0,05
20 ... 40 mg
0,1
40 ... 90 mg
0,25
100 ... 200 mg
0,5
200 ... 400 mg
