Application training on the vario MAX N/CN cube

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


• 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,


Introduction – Functional Principle

• N (Protein) / CN in accordance to DUMAS method


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.


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


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







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


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


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


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


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


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


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







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


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


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”)


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

28.09.2015 webinar | elementar | Appl. Train.

vario Max N/CN cube

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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


General procedure for optimizing oxygen dosing (matrix constant):


O2 flow from weight:

• base weight = max O2 flow → 600 mg ↔ 500 ml/min

• example: 264.30 mg ↔ 220.25 ml/min



O2 cut off threshold:

• percent of max. peak high where oxygen dosing stops

• example 5%: max. height = ca. 25,000; 5% ↔ 1,250



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


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







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


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


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







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


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