Organic Elemental Analysis 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 Capable of operating in 3 modes; CHN, CHNS and Oxygen Page 3
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 Page 4
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 Page 5
2400 Design Schematic Page 6 DetectionSeparationGas Control ZoneCombustion Zone
Combustion Process Completely combusting a weighed sample is critical to obtaining accurate results Page 7 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
Combustion Tube Page 9 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
Combustion and Reduction Packing Combustion Tube Silver Vanadate Silver Tungstate EA-1000 Reduction Tube 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 Removes excess oxygen Reduces NO X to Nitrogen Copper oxide at the end converts any CO to CO 2 Operates at about 640°C (the best temp is often debated)
Consumables N241-0680 CHN Combustion Kit 2 Combustion tubes & Chemicals 2000 runs N241-0681 CHN Reduction tube Kit 2 tubes 500 runs total Consumables are supplied individually or in kits
Gas Control Zone Homogenous mixture of product gases will achieve the highest precision Page 14 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
Separation Page 15 Frontal Chromatography Steady State Signal Simple difference calculation determines signal Easier to calculate a small step change than a small peak
Modes of Operation 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. Page 17
Sulphur 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 SO 3 and SO 2 The SO 3 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 CO 2 formed back to CO Acid gases are scrubbed in a trap installed on the side of the analyser
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 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 Page 27
Capabilities of EA 2400 Data Manager 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 Page 28
Queries Page 30 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
Advanced calculations and Statistics Page 31 Advanced calculations provide additional information on results 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 Page 32
Diagnostics Page 33 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
EA 2400 CHNS/O Analyzer Unique technology features and newest most modern Data Manager Software Page 35
EA 2400 CHNS/O Analyzer Operating the system Purging the analyser Blanks Conditioners K-Factors Samples Page 36
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 Page 38
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. Page 39
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 mins @ 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. Page 42
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) Page 43
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. Page 45
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. Page 47
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 Page 49
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 Page 52
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 Page 53
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 N241-1255Standard tin capsules. For solids and viscous, non-volatile liquids N241-1362Large tin capsules. For larger sample weights of solids with inert material(soil, silica beads) and lower carbon. N241-0320Volatile tin pans and covers. Requires sealer, 0219-0061. For volatile viscous liquids i.e. urea formaldehyde. 0240-06424 l aluminum capsules. Requires sealer B019-8093. For volatile, non- viscous liquids i.e. gasoline. 0009-0709 30 microliter aluminum capsules. Requires sealer B019-8093. For volatile, slightly viscous liquids. N241-1363Tin disks. For particulate material collected on a glass filter. N241-xxxxThick walled tin capsules for liquids
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
Filters 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.
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 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.
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 Signal Timing Make sure signals are properly timed
Filter Disks Install Filter disks on both sides of the cross- over and at the top of the Reduction tube 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