2400 Series 2
CHNS/O Analyser
Paul Gabbott PETA
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Organic Elemental Analysis
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The PE 2400 CHNS/O Elemental Analyzer is a combustion technique that determines
weight percent carbon, hydrogen, nitrogen, sulfur or oxygen in a variety of sample types
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Capable of operating in 3 modes; CHN, CHNS and Oxygen
Organic Elemental Analysis
 The 2400 is an organic elemental analyser
 It is designed to analyser organic materials such as those produced in
a chemical laboratory
 It is not designed for inorganics eg carbon in steel
 Nor is it a TOC analyser (total organic carbon). In some instances the
2400 could act as a TOC but it is not designed to continuously handle
applications such as TOC in seawater
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How does it work ?
 Combustion technique –
 Typically a sample is weighed into a tin capsule and placed in the
autosampler carousel.
 Information is entered into the instrument (ID & wt) and the run started.
 The sample is combusted into simple gases, CO2, H2O and N2,
collected in the mixing chamber, separated by frontal chromatography
and measured by TC
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2400 Design Schematic
Combustion Zone
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Gas Control Zone Separation
Detection
Combustion Process
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Completely combusting a weighed sample is critical to obtaining
accurate results
Static and Dynamic
4 steps to combustion
Sample introduced into oxygen environment
Additional oxygen introduced
Allowed to sit and burn
Additional oxygen introduced
Operator programmable
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CHN Combustion Tube
Combustion Tube
 Ultra high gases and pure quality reagents are required
Oxidizing & Removes interferences
i.e.,halogens and sulfur
Aids in the combustion of the sample
Prevents unwanted elements from interfering with the
analysis and keeps the system cleaner
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CHN Reduction Tube
Combustion and Reduction Packing
 Combustion Tube
 Silver Vanadate
 Silver Tungstate
 EA-1000
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Reduction Tube
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Copper 60-80 mesh
Pack the Copper as tight as you can
Cuprox
Copper Plug
Leave about ¼ inch space from top of
copper plug and the top of the tube
Reduction Tube
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Removes excess oxygen
Reduces NOX to Nitrogen
Copper oxide at the end converts any CO to CO2
Operates at about 640°C (the best temp is often debated)
Consumables
Consumables are supplied
individually or in kits
 N241-0680 CHN
 Combustion Kit
 2 Combustion tubes &
Chemicals 2000 runs
 N241-0681 CHN
 Reduction tube Kit
 2 tubes 500 runs total
Gas Control Zone
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Homogenous mixture of product gases will achieve the highest precision
Constant temperature, volume and pressure maintained in the mixing chamber
Environmental conditions such as changes in barometric pressure do not affect results
Achieve highest precision
Separates the combustion area from the separation area , so we can change the amount
of O2 without change in retention times
Mechanical mixing
Ensures a homogenous mixture of product gases
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Separation
Frontal Chromatography
Steady State Signal
Simple difference calculation determines signal
Easier to calculate a small step change than a small peak
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Frontal Chromatography
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Modes of Operation
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CHN mode is the most universal of the analysis
 CHN mode has the best reagent design and allows use of the Optimize Combustion
control parameters.
 Interfering elements (halogens and sulphur) are removed.
 CHNS mode designed to include sulphur, which reduces universality. This includes
limiting the range of sample types and sample size (1 to 2 mgs recommended). Metal
cations are excluded.
 Special care must be used in calibration and blanks for lower levels of sulphur.
 The Oxygen mode where oxygen in a sample is converted to carbon monoxide over
platinised carbon.
 This mode excludes compounds containing phosphorous, fluorine, silicon and metal
cations. Samples containing mineral matter must be demineralised prior to analysis.
 Upgradeability The user may choose any or all modes. The 2400 Series II may be freely
upgraded at any time to add additional mode capability to suit the needs of the
laboratory.
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Sulphur
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CHNS is determined in a similar manner to CHN
Sulphur separates after water so gives a step after water
This gives a longer analysis time
However the combustion tube is completely different
Sulphur Tube
Operating
temperature
around 975°C
Sulphur tube
 Sulphur burns to SO3 and SO2
 The SO3 must be removed (reduced) immediately because of
its reactivity
 This is achieved by adding copper to the combustion tube
 Normal catalysts are replaced with EA 6000 because they
scrub for sulphur
 Dynamic combustion conditions are required, and this restricts
the use of the ability to extend combustion time or add extra
oxygen
 CHNS does not use a separate reduction tube
Oxygen Analysis
 Oxygen is converted to carbon monoxide over platinised
carbon in a helium gas stream using silver capsules.
 Helium / hydrogen (approx 5%) gas stream enhances conversion to
CO and allows the use of tin capsules.
 Copper is used to convert any CO2 formed back to CO
 Acid gases are scrubbed in a trap installed on the side of the
analyser
Oxygen Tubes
Trap used with oxygen
Oxygen detection
Oxygen applications
 Often involve coals or fuels
 Note that coals must be demineralised for which procedures exist, but
it is not as simple.
CHNS and O2
 CHNS Tubes
 Copper
 EA-6000
Oxygen Tubes
Copper
Analysis Times
 Analysis times CHN: 6 min, CHNS: 8 min, Oxygen: 4 min
 Sample size 0 to 3 mgs typically depending on sample type. Small
samples will generally be limited by weighing errors, but may be used.
Large samples may be used if the combustible content is low
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Analytical Element Range (mgs)
detector range
C 0.001 - 3.6 S 0.001 - 2.0
H 0.001 - 1.0 O 0.001 - 2.0
N 0.001 - 6.0
Capabilities of EA 2400 Data Manager
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Collect and store complete run information
Search stored runs
Create reports
21 CFR part 11 compliant option
 audit trail
 signature points
 permissions
Complete analyzer history stored
 Instrument messages
 Leak test output
 Timing events
 Monitored components
Advanced calculations
Statistics
Recalculation capabilities
Archive data
EA 2400 Data Manager Main Run Window
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Queries
Specify your search using
AND/OR statements on
• sample ID
• date
• operator
• project
• run type
• mode
Set limits like
• is
• contains
• does not contain
• starts with
• between
• before
• after
• on
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Advanced calculations and Statistics
 Advanced calculations
provide additional
information on results
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 Statistics can be
preformed on a
set of runs
Printing reports and exporting data
 Print
 Table
 Report template
 Save to a file
 RTF
 TXT
 PDF
 Export formats
 Excel
 CSV
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Diagnostics
For confidence in instrument performance and for easy
evaluation of instrument history the operator can send vital
information to the database, including
 Instrument status
• temperatures
• pressures
• detector signals
• voltages
 Leak test results
 Parameter settings
 Purge times
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21 CFR part 11 compliance
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EA 2400 CHNS/O Analyzer
 Unique technology features and newest most modern Data
Manager Software
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EA 2400 CHNS/O Analyzer
 Operating the system
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Purging the analyser
Blanks
Conditioners
K-Factors
Samples
CHNS and CHN Purge Gases
 Gases : Helium and O2 @ 99.995 %
 N2 or Air for the Pneumatics @ 99.95 to 99.99%
Purging prior to analysis
 The analyser uses helium as a purge gas and oxygen as a
combustion gas
 Purge gases contain amounts of carbon, hydrogen and nitrogen which need to
be determined.
 In addition contaminants from the atmosphere get into the instrument
and gas lines, particularly overnight and when the system is left
unused.
 Purging is required to make sure the analyser and gas lines are free
of contamination before starting.
 The longer the gas lines the longer the purge times
 Oxygen is used only as required so the oxygen lines are more prone to
contamination when the system is unused
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System Purging
 Helium purge
 Use as long as found necessary to purge the analyser
 Afterwards a series of helium blanks can be performed to ensure the analyser
is free of contaminants
 Oxygen Purge
 Oxygen purging will pass through the copper tube and can cause a significant
loss in lifetime of the copper
 Oxygen purging should be kept to a minimum
 The end of the combustion tube may be loosened to allow oxygen escape
before the reduction tube.
 Gas Lines
 These must be copper or steel and completely free of leaks. Any leaks will
seriously compromise performance. As a result gas lines must be connected
straight to a cylinder and not used by any other equipment whatsoever.
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Leak tests
 Leak Tests
 #1 Mixing Volume
 #2 Combustion /Auto-Injector
 #3 Column/Detector
 Must pass Leak test 1
 Pressure should get to 760 mm,
you will here a click around
730mm. Pressure will hold for 5
min’s @ 760 mm.
 Test 2 will pressure around 780
to 800 mm, you may get a small
drop in pressure +/- 2 mm
 If this fails Check for Cracked
tubes, Auto-injector o-rings
Leak Tests
 Leak test 3 adds the
detector and column
 Cap sensing vent
 Sensing vent is the peek
tubing a yellow heat shirk
tubing on it
Blanks
 Blanks consist of running the system without any sample to determine
background levels of contamination. These are then subtracted from the
sample values.
 Tin (and all other) capsules contain levels of impurities which must be
measured so need to be included.
 Full oxygen blanks contain everything except a sample
 They use up copper at a high rate so should be kept to a minimum
 Helium blanks are run without oxygen or a capsule and are used to make
sure the system is purged, stable and ready to be used. They do not use
up chemicals so can be used freely.
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Conditioners
 Blanks decondition the system by removing adsorbed water from internal
surfaces
 A series of blanks will therefore continuously reduce the hydrogen
background value
 Any sample run afterwards will show lower levels of hydrogen than it
should because some of the water will be used to re-establish the
adsorbed water equilibrium.
 As a result a conditioner must be run after a blank.
 Normally this is a sample of the reference standard
 It does not have to be weighed because no use will be made of the
result, but normally this is good practice to make sure a sensible
amount is used, (eg – 2mg similar to a sample)
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Blank Values
Blank values are determined from a running average of
three blanks interspersed with conditioners. The
system automatically averages the results unless blanks
are run sequentially
The manual makes the following comments
K Factors
 K Factors are the calibration factors determined for each
element by running known standards.
 The step height of the signal for each element is measured in
microvolts per microgram (or whatever units the software uses)
of element present.
 Sample response divided by the K Factor allows the amount of
each element to be determined. This is converted to a weight
percent when the weight is known.
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K Factors
K factors are determined from the running average of three
or more values. Typical values as given by the manual are
shown below.
K-factors
 K-Factors
 should be run periodically to account for any drift or instability in the
system.
 Standards used
 Should be appropriate to the samples being run
 Eg if a 5% nitrogen standard is run with a 50% sample any error will
be magnified 10 times
 Different standards can be used for different elements if required.
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Typical Sart-up Sequence
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Check Leak tests
5 Helium blanks
Conditioner
Blank
Conditioner
Blank
Conditioner
Blank
Conditioner
3 K-Factors
Samples
Samples
 Solid samples are
encapsulated in tin foil
capsules which are folded
manually using a pair of
tweezers
 Care must be taken not to
tare the foil or lose sample in
this process
 This is one of the most
important and time consuming
aspects of analysis
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Weighing Samples
 Samples need to be
weighed to at least six
figures (microgram) level
 weighing accuracy of a 1mg
sample weighed to 6
figures is +/- 0.1%
 weighing accuracy of a 1mg
sample weighed to 5
figures is +/- 1%
Weight range specification
Total weight of each element must not exceed the analytical range below
Homogeneity
 Since samples are small they must be representative of the
material they are from
 Inhomogeneous samples should be ground and a small amount
of the resulting fines taken
 Potentially Inhomogeneous samples include
 Polymers and Composites
 Coals and minerals
 Solis and biological materials
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Liquid Samples
 Volatile free flowing liquids can be syringed into small
aluminium capsules (which contain around 2mg material)
sealed, and weighed.
 These are then inserted into tin capsules since tin aids the combustion
 Non volatile liquids can be inserted into thicker walled tin
capsules.
 It is always good to minimise the amount of aluminium put into the
combustion tubes – it can wet quartz and cause the tube to crack
 Viscous volatile liquids use ‘volatile’ aluminium pans more
frequently associated with DSC
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Liquid samples
 If a lot of aluminium is used
then the quartz tube may
need to be protected. This
can be done using zirconia
cloth, or a sacrificial quartz
inner tube.
 Do not cool the furnaces
overnight and replace the
vial receptacle more
frequently
Handling Samples
 N241-1255
Standard tin capsules. For solids and viscous, non-volatile liquids
 N241-1362
Large tin capsules. For larger sample weights of solids with inert
material (soil, silica beads) and lower carbon.
 N241-0320
Volatile tin pans and covers. Requires sealer, 0219-0061. For
volatile viscous liquids i.e. urea formaldehyde.
 0240-0642
4 l aluminum capsules. Requires sealer B019-8093. For volatile, nonviscous liquids i.e. gasoline.
 0009-0709
30 microliter aluminum capsules. Requires sealer B019-8093. For
volatile, slightly viscous liquids.
 N241-1363
Tin disks. For particulate material collected on a glass filter.
 N241-xxxx
Thick walled tin capsules for liquids
Accuracy Specifications
Optimise Combustion
Optimise Combustion
 For most CHN work the extended combustion time can be set
to 10 – 20 seconds
 Increased oxygen usage should be avoided if not needed since
it reduces the life of the copper tube.
High carbon containing samples
POLYNUCLEAR AROMATICS
These are quite demanding materials due to high Carbon
content and difficult to burn structure. Typically limit max
sample size to about 2.5mg, add extra combustion time
and extra oxygen if incomplete combustion is found.
Incomplete combustion
 Quite rare but may occur with very high carbon containing
materials or if the combustion tube needs to be changed
 How is this evident
 Increasing carbon background (blank)
 Production of methane (shows as a high nitrogen / low carbon result)
 Remove residue by running some oxygen blanks or Purge with
oxygen to burn any remaining carbon
 Extend combustion time and amount of available oxygen for
future runs or reduce sample weight.
High carbon containing samples
Carbon Fibre
Increase combustion furnace to 980°C
Max weight around 2mg
Low combustible (carbon) content
SOILS
Soils work well on the 2400 because higher wts can be used
and the furnace conditions can be optimised to burn them.
Samples should be well dried first.
I typically work with approx 20mg samples thought weights can
be higher if required, add 20 seconds to combustion and add a
second to oxyfill and oxyboost1
Coal
 Actually it does not burn easily
 Needs time and available oxygen, but 20 secs extended combustion
and typically 2 secs extra oxygen are sufficient
 Homogeneity is always an issue and how well it is ground
 Moisture content is another, usually it is analysed after drying
 Usually analysed for its calorific content which is calculated
from its elemental composition
Particulate matter in water or air
 This is an increasingly common requirement
 Applications include air quality
 exhaust emissions
 Plankton in seawater
 Material is collected on filter discs which can be analysed
completely in the 2400
Rolling up a glass fibre filter disk
Filters
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Use a sacrificial quartz liner
Do not drop furnace temps in case of wetting
Extend combustion times
Calculate C/N ratios
Silicon containing compounds
May form a stable silane or the extremely stable silicon
carbide. The general approach to analysis of this type of
material is to add vanadium pentoxide to the capsule if
required. Tin also promotes combustion of this type of
material , one reason for using it.
Refractory carbides
Organometallic compounds
As with silicon containing compounds these are susceptible to
the formation of stable carbides, eg boron carbide which is a
stable glass. The tin capsule acts as a combustion aid but if
difficulties emerge then vanadium pentoxide should be added
to the capsule.
Mercury containing complexes
 If mercury compounds are in use then as a precaution add
pelleted gold to the combustion tube to trap any potentially
volatile mercury produced
 REPLACE TUBE AFTER THE ANALYSIS HAS FINISHED
 Use a similar approach with other potentially hazardous metal
complexes
 most will produce stable oxides
 The tube catalysts and the copper tube are actually very good
at scrubbing for these products
 It is therefore good practice to replace the combustion tube regularly
before any unwanted elements pass through the system
Varying H content
 The equilibration effect of water during blanks has already been
noted
 It also has an effect as samples are run
 High H followed by low H will result in a higher value for the low
H material than it should have.
 Low H followed by high H will result in a low value for the latter
material
 All results are should still be within specification but these
effects are easily noticeable.
Effect of a hydrate
Water content has a significant effect on results
as shown in this example of a hydrate. Solvates
also have a significant effect.
Effect of Solvate / Hydrate
 Calculations exist that allow
the operator to fit the data to
a known solvate. However
the material may not be fully
solvated which causes
difficulties
Effect of moisture
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It is no surprise that moisture has a similar effect
If a sample is not dry then accurate CHN data is difficult
It can be back calculated but again this is not ideal
Impure (wet) samples give inaccurate results
Sulphur
 CHNS determination works but the system is not as optimised
as for CHN
 Additionally the separation of water and sulphur is not complete
 This makes determination of low levels of sulphur difficult
unless the water is removed using an in-line trap.
Final practical comments
Drying the catalysts
 The EA 1000 and silver tungstate on magnesium oxide are best
dried before use.
 Use a muffle furnace at 900°C for 30 minutes, longer at lower
temps
 Store in a dessicator
 Damp material leads to high hydrogen blanks that drift down
and the water evolved can also promote devitrification of the
quartz
Diagnostics-Signal Timing
Make sure signals are properly timed
Signal Timing
Filter Disks
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Install Filter disks on both sides of the crossover and at the top of the Reduction tube
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This will help in keeping the cross-over and
the parts after the reduction tube clean
Place filters on both side of the cross-over
and the top of the reduction tube
CHN Reduction Tube
 Copper reduction tube with
support for filling
 If not properly filled this is
the main cause of drift in an
analyser
 Wire form copper is easier to
pack but is less efficient
 Copper powder gives the
longest life but often settles
in use