Application Training on the vario MAX N/CN cube
September 24th, 2015
Dr. Tony Szuppa
Webinar
Your host
• Dr. Tony Szuppa
• joined Elementar in Feb. 2014
• manager application laboratory
• responsible for sample management, application trainings,
customer support
• PhD in environmental chemistry in Oct. 2010
28/09/2015 Sample preparation in elemental analysis - webinar - 2
28.09.2015 webinar | elementar | Appl. Train. vario Max N/CN cube 3
Content Introduction 1
Sample Preparation 2
Running Improvements 3
Maintainance Improvements 4
Special Matrices 5
Introduction – Instrument Versions
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• two versions available: N/CN vs. CNS
• main differences:
• furnace temperatures
• tube filling and materials
• gas handling (drying, columns)
• today: focus only on N/CN
Introduction – Application Fields
• Food
• protein analysis in milk, meat, cheese
• low N determination for beer, starch, gluten-free
products
• Feed
• protein analysis in animal feed
• control of feeding procedure
• Agriculture:
• C/N ratio in soil, plant material, fertilizer,
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Introduction – Functional Principle
• N (Protein) / CN in accordance to DUMAS method
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Introduction – Combustion & Reduction
• C – combustion tube at 900 ºC
• CuO: oxidizes sample to CO2, NOx, H2O other gases
• P – post combustion tube at 900 ºC
• CuO/Pt: oxidizes CH4 and CO from incompl. comb.
• Ag wool removes halogens
• R – reduction tube at 830 ºC
• tungsten: turns NOx to N2, removes O2 and sulfur comp.
• CuO/Cu: traces of CO and NOx turned into CO2 and N2
• zinc: removes halogens and sulfur comp.
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C P R
Introduction – Drying / Separation
• 3-Step drying:
1. physical water removal by condensation at cooled tube
2. physical water removal by membrane dryer
3. chemical water removal by Sicapent® tube
• Separation: Purge & Trap – Technology
• two trapping columns for CO2 absorption (He mode)
• per run only one columns is used, cool down of the other one cold
column → CO2 trapped; hot column → CO2 released
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Introduction - Detection
• TCD – Thermal Conductivity Detection
• reference gas (He, Ar) → baseline
• other gases → signal
• N2 runs directly trough → 1st peak
• CO2 released from column → 2nd peak
• other gases removed → no peak
• N mode: CO2 is release to ambient air
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28.09.2015 webinar | elementar | Appl. Train. vario Max N/CN cube 10
Content Introduction 1
Sample Preparation 2
Running Improvements 3
Maintainance Improvements 4
Special Matrices 5
Sample Preparation – Sample Weighing
• typical lab balance: +/- 0.1 mg accuracy
• usually not critical for sample quantities > 50 mg
• critical for calibration, applying sample weight < 10 mg
solution: - more replicates
- calibration kit’s from EAS
available
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Sample Preparation – Open Vessel vs. Wrapping
Problem: Hot gripper arm
• liquid samples easily self-degrade on air
(solution of urea or ammonia)
• samples with low point of boiling / digestion
(acetanilide, etc.)
Solution:
• absorb liquids on inert material (e.g. SiO2, Al2O3, etc.) or
• put liquids into tin capsules
• wrapping or cover solid samples with tin foil
• using other standard material
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Sample Preparation – Open Vessel vs. Wrapping
Problem: blank removal by gripper arm
• through middle of gripper arm He(Ar) is dosed to remove
blank before transfer into furnace
• inside furnace O2 is dosed for combustion
• light particles (powder, dust, etc.) can be carried out of
crucible before entering furnace
Solution:
• wrapping or cover solid samples with tin foil
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Sample Preparation – Typical Sample Quantities
For best results:
• measuring value has to be in the middle of the calibration
• element concentration not out of range (500 mg), even only measuring N
• C content influence combustion behavior → high C, low quantity
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Sample Matrix Rough C content Sample Quantity
Standard (e.g. glutamic acid) 40% 200 mg - 250 mg
Food, Feed, Plant, etc. 20% - 40% 500 mg
Liquids (milk, beer, manure) <1% 1.5 ml – 2.5 ml
Soil <5% 1000 mg
Oil 90 0.1 ml
Sample Preparation – Typical Standards for daily factor
• results independent from Matrix, free choice of standard material
• different substances: - for calibration
- for daily factor
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Standard C content N content
glutamic acid 40.82% 9.52%
aspartic acid 36.09% 10.52%
EDTA 41.10% 9.59%
Lysine 49.30% 19.16%
Urea 20.00% 46.65%
…
Sample Preparation – Typical Standards for daily factor
• special attention to low or high range elemental concentration
• self-made liquid standards
• certified reference materials
* Tris(hydroxymethyl)-aminomethan
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Range Standard Application
low N 1000 ppm solution of TRIS* liquids, beer, milk
low N certified starch (LGC, NIST) gluten-free products, starch
high N melamine (N% = 66.64%) Flame inhibitors, plastics
low C certified soil Soil, sludge, sediments
high C stearic acid oil, plastic
Sample Preparation – Blank handling
• Blank without crucible: 50 – 150 AU
• Blank with crucible: large variety for C, for N usually no higher blank
• not important for C concentration > 1%
• to subtract from measuring value non-applicable due to variety
• For lower concentration or calibration:
• Heat out crucible by 950 ºC with analyzer or external furnace
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Content Introduction 1
Sample Preparation 2
Running Improvements 3
Maintainance Improvements 4
Special Matrices 5
Running Improvements – Typical Start-up
• after instrument is ready to use → blank
• Blank measurements with or without O2
• for conditioning → RunIn
• for validation → daily factor
• for analyzing → sample measurements
• after run → validation re-check, blank
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Running Improvements – Correct Method Selection
• method regulates: oxygen dosing, peak integration
• software includes method library for different matrices
- glutamic acid
- plant
- oil
• if matrix is not listed compare carbon content
• rule of thumb I
high C cont. → long oxygen dosing
→ rough peak anticipation
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Running Improvements – Correct Method Selection
• similar C content → same method
• same regarding extra ordinary N values
very high N → rough peak anticipation (method: “urea acid”)
very low N → enlarged peak anticipation (method: “starch”)
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Matrix C content Method
milk, beer, manure, liquids low milk, beer
feed, whey, plant, wood middle plant, cereals
oil, fat, bacon, sausages cheese
high oil, butter, cheese, bacon
Running Improvements – Oxygen Dosing
Correct oxygen dosing depends on carbon content:
• too much oxygen has to be removed by W (short live time)
• too less oxygen yield in sooting → wrong results for C%
Rough guess: 1 g organic substance consumes 0.8 – 1.0 l O2
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Running Improvements – Oxygen Dosing
1. Select method fits best to your sample comparing know C%
2. Run some repetitions of the sample by constant weight.
3. Reduce oxygen dosing time until peak tails and C%
decrease, no change in flow rate
4. Set oxygen dosing time back to last good result
5. Select O2 cut off threshold of 10-15%
6. Select O2 flow from weight and set base weight
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General procedure for optimizing oxygen dosing (matrix constant):
Running Improvements – Oxygen Dosing
O2 flow from weight:
• base weight = max O2 flow → 600 mg ↔ 500 ml/min
• example: 264.30 mg ↔ 220.25 ml/min
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Running Improvements – Oxygen Dosing
O2 cut off threshold:
• percent of max. peak high where oxygen dosing stops
• example 5%: max. height = ca. 25,000; 5% ↔ 1,250
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Running Improvements – Oxygen Dosing
Important:
• N results nearly independent from oxygen dosing
R-N-R’ red. atm.
N2 + CO + CH4 + H2
• catalyst material buffers too low oxygen dosing for some samples
• too less oxygen dosing shorten lifetime of tube filling
CO + CH4 + H2 + CuO → CO2 + H2O + Cu2O
• Blank with O2 and RunIn to re-activate catalyst
O2 + Cu2O → CuO
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Running Improvements – Adaption Tube Filling
• CuO/Pt for oxidation of carbon compounds
• high carbon content→ formation of CH4
• more Pt for better conversion to CO2
• Standard: 30 g
• For Oil, fatty samples: 40 – 50 g
• lower CuO to keep same filling height
• formation of N2 is not effected
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28.09.2015 webinar | elementar | Appl. Train. vario Max N/CN cube 28
Content Introduction 1
Sample Preparation 2
Running Improvements 3
Maintainance Improvements 4
Special Matrices 5
Maintenance Improvements – Saving Tubes Lifetime
Stainless steel tubes
• usually re-useable for 4000 to 6000 runs
• corroded by aggressive matrices: salts, halogens,
phosphates, etc.
(salami, sausages, soy-sauce, fish meal, etc.)
• lifetimes reduces to <2000 runs
• using two tube alternating for 200 runs max
• remove filling, if possible re-use
• clean tube with water to remove contamination
• after air drying re-fill
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Maintenance Improvements – Saving Tubes Lifetime
Tungsten
• used to remove O2, SO2
• Used to reduce NOx to N2
• conversion from W to WO3
• using of spacers due to increasing volume
• danger of tube bursting when too much W
• weight in max. 19 g W, don’t use delivered spoon for
portioning
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Maintenance Improvements – Correct Filling
Dosing of mixed filings: CuO + corundum balls
CuO + Pt
• pre-weight in acc. to manual
• do not mix before, different density!
• transferring into to tube simultaneously
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Content Introduction 1
Sample Preparation 2
Running Improvements 3
Maintainance Improvements 4
Special Matrices 5
Special Matrices – Carbon-free Samples
Inorganic fertilizers, e.g. NH4NO3
• No carbon source to reduce nitrate ion
• addition of easy to combust C source, e.g. sucrose,
lactose, etc.
• carbon reduces nitrate to form N2
• results for C% are use-less
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Special Matrices – Aggressive Matrices
salty (halogen) samples
• sausages, soy sauce, plants, soil
• formation of HCl →corrodes metal parts like tube, plugs, connectors
NaCl H2O
HCl; HCl + Fe → FeCl3
• reduce sample quantity to a minimum
• regular cleaning of tubes etc. with pure water, to remove formed
metal salts
• if necessary, addition of iron chips to sample as sacrificial material
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Elementar thanks for your attention!
Nice to know we are strong family.
webinar | elementar | Appl. Train. vario Max N/CN cube