BUCHI DuMaster D-480 - Manual (Page 47)

Operation Manual D-480 ©BÜCH Labortechnik AG
4 - Understanding the instrument and planning its use 47
Sample insertion and initiation of measurement
Introduction
The following section explains how to insert the analysis samples into the combustion tube and how
to initiate measurement of the reaction products.
Note
The bracketed numbers used below refer to the part numbers listed in Functional units (on page
43).
Sample insertion processes and initiation of measurement
Sample insertion and initiation of measurement is divided into the following phases:
 The thermal conductivity detector (9, 10) performs autozero adjustment of the measuring signal.
 A complete pressure drop takes place in the system, together with the emptying of water
accumulated in the water condenser (8).
 The ball valve (2) opens by turning the ball through 90°.
 The carousel (1) moves one step and the sample drops through the ball valve (2) onto the closed
Ni flap.
 The ball valve (2) turns through 90° and closes the apparatus.
 The carrier gas is reactivated and and the atmospheric nitrogen will be flushed out.
 After expiration of a flushing time (Ni flap delay) the Ni flap opens for a short period by means of
a pivoting magnetic field.
 The sample drops into the ash crucible (5) of the combustion tube (4) and is heated up to the
combustion temperature.
 Oxygen dosing into the ash crucible begins.
 The integrator reset resets integration display to zero. N integration begins.
Substance digestion and preparation of the reaction gas mixture
Introduction
The following section explains
 what processes take place in the combustion, post combustion and reduction tube of the furnace.
 how the reaction gas mixture is prepared for the nitrogen determination.
Note
The item numbers used below refer to the picture in Functional units (on page 43).
Processes during substance digestion and preparation of the reaction gas mixture
Substance digestion and preparation of the reaction gas mixture is divided into the following phases:
 The atmosphere in the combustion tube (4) is enriched with oxygen. Nitrogen bound in the
sample burns to form N
2
and NO
X
. Halogen bound in the sample reacts to form volatile halogen
compounds, sulfur reacts to form SO
2
and SO
3
, hydrogen reacts to form H
2
O and carbon reacts
to form CO
2
.
 The carrier gas flow transfers the gaseous combustion products into the post combustion tube (6)
and reduction tube (7), where the following processes take place:
 In the reduction tube, nitrogen oxides are quantitatively transferred at the tungsten contact
to form molecular nitrogen. Excess oxygen is bound.
 Sulfur absorption takes place in the reduction tube at the tungsten.