How to determine carbon, nitrogen, and other parameters · PDF fileHow to determine carbon,...

IMPRS-gBGC workshop 'Analytical Techniques', September 15th 2016

How to determine carbon, nitrogen, and other parameters in solid and liquid samples?

Ines Hilke, RoutineMeasurements & Analysis

How to determine carbon, nitrogen, and other parameters in solid and liquid samples?


09:00 Overview of analytical methods (e.g. elemental analysis, sum parameter analysis, flow injection analysis, and ion chromatography) No limits? - instrumentation, pro and cons of application - break - ~ 11:00 Demonstration of analytical methods and laboratory instruments (lab A1.019) - lunch break - 13:00 Analytics of solid and liquid samples (lab A1.019)

Overview RoMA


the lab:

• service facility of the institute provide analytical primary data for scientists and PhD students

•main focus determination of carbon and nitrogen in very different kinds of samples •data used within a broad spectrum of research projects (e.g. CarboEurope-IP, Jena

Experiment, Biodiversity Exploratories, AquaDiva, MANIP-Spain …) the basic concept of our routine work:

•high precision & accuracy of the measurements • to master a very large number of samples ~ 30’000 per year • samples have to be analyzed rapidly when many projects are limited by short time

frames besides routine analyses:

•analytical solutions adapted to scientific requests •assist our clients with technical and chemical support


RoMA – Our lab lab equipment: established according to the scientific focus of the institute modular systems, depending on research projects •objective of research: which analytes? which kind of samples / matrix?

•experimental design, statistics: sample number and quantity?

sample preparation? sample pretreatment?

separate or simultaneous quantification? detection of trace amounts?

quality management: •accuracy trueness (proximity of measurement results to the true value) precision (repeatability and reproducibility of the measurement) •traceabilty evaluated data row data, data storage, archiving

Retreat MPI BGC, Bad Sulza, November 2009

RoMA – Instrumentation

Elemental Analysis •"vario EL II" (Elementar Analysensysteme GmbH, Hanau) for C, N, [H, S] in plants / soils •"vario EL II" (Elementar Analysensysteme GmbH, Hanau) for C, N, [S] in plants / soils •"vario Max" (Elementar Analysensysteme GmbH, Hanau) for C, N in soils •"CS 500" (Eltra GmbH, Neuss) for C, [S] in soils Sum Parameter •"high TOC" (Elementar Analysensysteme GmbH, Hanau) for DOC / TOC, DIC / TIC in water samples / extracts •"vario TOC cube" (Elementar Analysensysteme GmbH, Hanau) for DOC / TOC, DIC / TIC in water samples / extracts •"TN-100" (a1 envirotech Düsseldorf) for TNb in water samples / extracts Flow Injection Analysis •"Quikchem QC85S5" (Lachat Instruments, Hach Company, Loveland CO, USA) for NH4+-N, NO2--N, NO3--N, PO43--P, SO42- in water samples / extracts Ion Chromatography •"DX 500" (Thermo Fisher Scientific GmbH, Idstein) for F -, Cl -, Br -, NO2-, NO3-, PO43-, SO42- in water samples / extracts •"ICS-5000" (Thermo Fisher Scientific GmbH, Idstein) for Li+, Na+, NH4+, K+, Mg2+, Ca2+ in water samples


RoMA – Analytical Approaches 12.011

6 2.5

C -4, 2, 4 He 2s2 2p2

Carbon (solid samples) Elemental Analysis (high temperature combustion, 1150°C): total carbon content in soils, sediments, rocks, litter, plants, other solid

materials

vario MAX vario EL thermal treatment of soil samples

4 M HCl

acidification of soil samples

Thermal or Acid pre-treatment of samples: separation of inorganic and organic carbon

• effects of land use, management, and biodiversity on SOC • variability and changes of SOC stocks • effects of neighboring plants on biomass production ……

to study



6 2.5

C -4, 2, 4 He 2s2 2p2

Carbon (liquid samples)

Sum Parameter Analysis (high temperature combustion, 1050°C) dissolved inorganic (DIC) and organic carbon (DOC) in water samples, soil

solution extractable organic carbon in water, KCl- solution, K2SO4 -solution

sample preparation and instrument maintenance

high TOC

• fluxes of DIC / DOC • mobile and easily available C fractions • microbial carbon ……

to investigate



6 2.5

C -4, 2, 4 He 2s2 2p2

Carbon (liquid samples)

Sum Parameter Analysis (high temperature combustion, 850°C) dissolved inorganic (DIC) or organic carbon (DOC) in water samples extractable organic carbon in KCl-solution, K2SO4 -solution samples with little volume

sample preparation and instrument maintenance

high TOC

• fluxes of DIC / DOC • mobile and easily available C fractions • microbial carbon ……

to investigate


RoMA – Analytical Approaches

Nitrogen (solid samples)

Elemental Analysis (high temperature combustion, 1150°C): total nitrogen content in soils, sediments, litter, plants, other solid

materials

• data of carbon and nitrogen determination can be used to estimate the degradabiltiy of soil organic matter

• the additional measurement of hydrogen and sulfur provides information on the chemical composition of organic substances

14.007

7 3.1

N -3, 2, 3, 4, 5 He 2s2 2p3

vario MAX vario EL



Nitrogen (liquid samples)

14.007

7 3.1

N -3, 2, 3, 4, 5 He 2s2 2p3

Sum Parameter Analysis (high temperature combustion, 800°C)

total nitrogen (TNb) in water samples, soil solution extractable nitrogen in water, KCl-solution, CaCl2-solution, K2SO4-solution

TNb [mg/L]

equimolar mixture according DIN-standard EN 12260

0 2 4 6 8 10 12 14 16

units

of a

rea

20

40

60

80

100 NO3

--N

NH4+-N + NO3

--N organic N NH4

+-N

high TOC

units

of a

rea

TN-100 TNb [mg/L]

0 4 8 12 16 20

0.5e+7

1.0e+7

1.5e+7

2.0e+7

2.5e+7

organic N

NH4+-N

NO3--N

TN-100

• mobile and easily available N fractions • microbial nitrogen • organic nitrogen

to investigate




14.007

7 3.1

N -3, 2, 3, 4, 5 He 2s2 2p3

•organic nitrogen in water samples, soil solution

Norg = TNb – NH4+-N – (NO3

– -N + NO2

– -N)

Ion Chromatography System

•ammonium-nitrogen NH4+-N , (nitrate + nitrite)-nitrogen NO3–-N + NO2

–-N Flow Injection Analysis with photometric detection •ammonium NH4

+, nitrate NO3– , nitrite NO2

– Ion Chromatography with conductivity detection / NO3

– , NO2– UV detection

Flow Injection Analyzer




14.007

7 3.1

N -3, 2, 3, 4, 5 He 2s2 2p3

Norg = TNb – NH4+-N – (NO3

– -N + NO2

– -N)

222CBAD ssss ++=D = A – B – C

• deviation of each parameter is important for calculation of Norg • the analytical approach with the highest deviation determines the accuracy

of Norg

a2

b2 c2 c2 = a2 + b2

22 bac +=

a2

b2 c2

units

of a

rea

TN-100 TNb [mg/L]

0 4 8 12 16 20

0.5e+7

1.0e+7

1.5e+7

2.0e+7

2.5e+7

organic N

NH4+-N

NO3--N

TN-100



30.974 15 P

32.066 16 S

18.998 9 F

35.453 17 Cl

79.904 35 Br

total contents in soil samples, plant material EA sulfate: SO42- in water samples Ion Chromatography (IC) sulfate: SO42- in soil extracts Flow Injection Analysis (FIA)

fluoride: F- , chloride: Cl- , bromide: Br- in water samples IC

1.0079 1 H

total contents in plants and other organic materials Elemental Analysis (EA)

phosphate: PO43- in water samples IC phosphate: PO43- in soil extracts Flow Injection Analysis (FIA)



40.078 20 Ca

39.0983 19 K

54.938 25 Mn

Na+, K+, Ca2+, Mg2+, Mn2+, in water samples Ion Chromatography (IC) with conductivity detection

22.9898 11 Na

24.305 12 Mg

www.bgc-jena.mpg.de/service/chem_lab/roma/


Solid Samples: Sample Preparation

Sample preparation is an essential part of analysis and influences analysis results directly. • research objective, statistics, experimental design sample number,

sample quantity • data base, create samples & sample names, print labels, barcode • preparation of sampling: equipment and labelling • time management • check for clearness sample names (e.g. combine the sample name

project; contributor, content / description / plot name & number, - sampling date)

• do not overwrite errors! cross the mistake and add the right name • subsamples labelling • sample preservation • sample storage / archiving


Solid Samples: Elemental Analysis

Analysis: • T combustion tube, closed at the left side, containing the sample + CuO (both mixed), and KClO3 (to release O2

after separate heating [= „post-combustion“ ] / O2 as oxidizing agent and carrier gas • G „oven“ (coal) • A U-shaped tube, filled with H2SO4 -wetted CaCl2 to adsorb H2O vapour • B glass balls, containing KOH (liquid) to adsorb CO2 • C U-shaped tube, filled with KOH pellets (solid) to catch trace amounts of CO2

Quantification of C, H, O: • difference of weights before and after combustion (A as well as B and C) results in contents of H2O and CO2 (H

and C) • difference to the total sample weight results in content of O

apparatus for analysis of organic compounds (nitrogen-free) according to J. v. Liebig (1803-1873), 1831

(ref.: J. Langlebert: Manuel de Chimie. Impr. Jules Delalain et Fils. Paris 1875 (25th edition)



1) autosampler: without or with

ash removal

2) reaction: high temperature combustion oxidation / reduction catalysts

3) separation: adsorption columns

„purge & trap“

4) detection: infrared spectroscopy and / or thermal conductivity detector

vario EL vario MAX

(ref.: J. Langlebert: Manuel de Chimie. Impr. Jules Delalain et Fils. Paris 1875 (25th edition)


Elemental analysis does not just start by inserting the sample into the combustion tube! For soils: the soil skeleton, fine roots, soil animals and their remains have to be removed.

In general: • Does the sample have acceptable homogeneity? • Is drying necessary? • Is sample wrapping necessary? • Are additives necessary or recommended? • What is the correct sample weight?


ref.: Ruppenthal, Marc (Product Manager Elemental Analysis, Elementar Analysensysteme GmbH) Sample preparation in elemental analysis. Webinar, 2016


Solid Samples: Elemental Analysis “fine soil”: soil skeleton, fine roots, soil animals and their remains have to be removed.

Differences in OC-Stock [kg m-2] and CN ratio after graduated sorting of roots from soil samples.

Carbon content data are often taken as a basis for further calculations, e.g. for estimation of mass balance as well as for modelling. Small errors can effect huge differences in total (table). For example, data of organic carbon originated from soils with different accuracy levels in root extraction can result in high valuation discrepancies of total carbon stocks.

Organic carbon data from one soil with different accuracy levels of root extraction


Does the sample have acceptable homogeneity?

Organic carbon (Corg)[%] and coefficient of variation of soil samples with and without grinding.

Visible structures of insufficiently compared to well homogenized soil.

Elemental Analysis


dry mass content [%] = sample weight, absolute dry 105°C [g] / sample weight, air dry 40°C [g] * 100% o C[%](105°C) = C[%](40°C) / (dry mass content [%])

o N[%](105°C) = N[%](40°C) / (dry mass content [%])

o S [%](105°C) = S[%](40°C) / (dry mass content [%])

Is drying necessary? • wet materials like field-fresh soils or plants need to be stabilized before further treatment to

inhibit microbial alterations • soils, in general, are dried at 40 °C [Schlichting, E. 1995], provided that microbial analyses

are not planned (“air-dry” samples, common expression in soil analysis)

• the calculation of contents, however, is usually related to “absolute dry” samples at 105°C to overcome differences in water absorption from ambient air

• moisture decreases carbon, nitrogen, sulphur concentrations, because: the results of

elemental analysis are calculated as mass %


• however: moisture (H2O) increases hydrogen and oxygen concentrations of a sample 105°C or freeze drying



Variation in absorption capacity depends on the sample matrix. Clayic materials are prone to such effects, followed by humic substrates. To handle this rarely known and never constant value, the residual water content of air-dried soil samples has to be determined at the same time of weighing for carbon- or other content analysis [Schlichting, E. 1995].

Difference of corrected and not corrected Corg [%] in relation to dry mass corrected Corg [mass%] which depends on daily shifting variables.

Difference of corrected and not corrected Corg [%] in relation to dry mass corrected Corg [mass%] which depends on sample matrix.



Is sample wrapping necessary?

Wrapping: necessary for voluminous / fluffy material (e.g. freeze dried humic substances) to eliminate the enclosed air (78,08 Vol.-% N2 !) Wrapping material: should not produce blanks! tin capsules / boats exothermic oxidation of tin locally increases the combustion temperature to ~ 1800 °C, supporting the combustion aluminum capsules / boats no exothermic reaction of aluminum inside the combustion furnace, suitable analysis of explosives silver capsules / boats absorbs halogens, recommended for samples with very high halogen content or samples with acid pretreatment; endothermic reaction additional packing with tin foil recommended




fluorine adsorption kit samples containing F / HF destroy the quartz glass in CHNS/CNS/S modes (high temperature mode), attack the SO2 purge & trap column, and can create dummy peaks of C or S 4HF + SiO2 2H 2O + SiF4 addition of MgO MgO + 2HF MgF2 + H2O use of ceramic consumables

Are additives necessary or recommended?

addition of WO3 for S analysis of soils, sulfates (up to 10:1) for adsorption of alkaline ions (1:1) not necessary for organic S

Additives improve recovery of analytes and lifetime of consumables.




What is the right sample weight?





Solid samples: Elemental Analysis

Please use a suitable balance. Balance and elemental analyzer represent one analytical system. If the weighing is not done carefully, the analysis will be wrong. Even with the best elemental analyzer on earth! lab / weighing room • should be as vibration-free as possible • corners are the most vibration-free areas of a building • level and adjust the balance whenever it was moved weighing bench • stable, no transfer of vibrations (no plastic or glass) • antimagnetic (no steel table) • protected against electrostatic charge positioning of the weight („corner load“) • always place samples in the center of the weighing pan temperature • indirect influence: temperature gradient between weighing sample and the surrounding

produces air-current • direct influence: temperature dependent drift of the balance • condensation of ambient humidity on the surface of the vessel





air circulation • do not place the balance in the air flow of ventilators (computer, analyzer) • do not place the balance next to a door • people who pass the working place can cause turbulence humidity • balances should never used >80 % and < 20 % air humidity light • direct sunlight radiation (heat) influences the weighing process convection • volatile or hygroscopic substances can cause a drift of the balance (evaporation of the sample or

uptake of ambient humidity) magnetism • magnetic force will be interpreted as a load by the balance (magnetic material, magnetic stirrer) electrostatic charge • materials with low electrical conductivity, glass, plastics, powder or granulates can carry

electrostatic charges, dry air (< 40 % humidity) increases the incidence of this effect • caused by handling of containers or materials

− pouring liquid or powder from one container to another, − use of gloves − wearing synthetic clothes





sample weight / quantity depends on • available sample material • type of samples • working range of the elemental analyzer Note: aggressive samples (high halogen or salt content) should be analyzed with the lowest possible weight to increase lifetime of both, consumables and instrument test measurements are recommended with low weights of some representative samples to estimate the contents of carbon, nitrogen, and other analytes in question and to determine the proper sample weights for the whole sample set

https://www.bgc-jena.mpg.de/bgp/index.php/Internal/Methods detailed information about methods of sample preparation



Analytical Principle


• various kinds of solid material, in general plant and soil samples can be measured • samples have to be weighed into special sample containers • the autosampler transfers the samples into the combustion tube filled with tungsten trioxide (WO3) and heated

to a temperature of 1150 °C (vario EL) and 1100 °C (vario MAX), respectively • when the samples are introduced, the carrier gas helium is temporarily mixed with pure oxygen • flash combustion takes place, in case of the vario EL analyzer primed by oxidation of the tin boats • quantitative oxidation is achieved by passing the gases over the catalyst, the vario MAX analyzer is additionally

equipped with a second combustion tube filled with a blend of copper oxide and platinum, and heated to a temperature of 900 °C.

• once the combustion of samples has been accomplished the gas mixture flows into a reduction tube filled with copper powder (vario EL) and tungsten (vario MAX) respectively, heated to a temperature of 850 °C (vario EL) and 830 °C (vario MAX) respectively

• …. next slide




• the excess oxygen is eliminated by the heated copper, the nitrogen oxides are reduced to nitrogen • small packing of silver wool adsorbs any halogens if present • the gases are separated by a system similar to that of gas chromatography (purge and trap). • nitrogen passes through these columns without delay and it is measured by the thermal conductivity detector

(TCD). After integration of the nitrogen signal, carbon dioxide is released from the adsorption column, passed to the TCD, and measured.

• once the instrument has been calibrated by the use of pure organic reagents, a daily factor is determined by regular re-analysis of these chemicals. The factor is determined after analysis of about every 20 samples to correct a possible drift.

• to prove the accuracy and reliability of the results, reference materials are analyzed on a regular basis. • one analysis lasts 12 - 15 min depending on the C and N content of the measured samples.


Separation of total organic carbon (TOC) and total inorganic carbon (TIC)


Basic steps for analytical determination of the carbon sum parameters

separation of the sum parameters can be carried out in a • chemical or • thermal pretreatment step

In both cases, the treated sum parameter will be destroyed, i.e. it will be converted to CO2. For some applications, the conversion product can be used directly for subsequent quantification. Both techniques, chemical and thermal pretreatment, allow direct or indirect quantification of TOC and / or TIC.

sampleTC

CnHm & CaCO3

chemical pretreatment:sample + diluted mineral acid

thermal pretreatment:sample + defined temperature

(¼ m+n)O2 + CnHm & CaCO3nCO2 + ½ mH2O + CaCO3

2HCl + CnHm & CaCO3 CO2 + H2O + CaCl2 + CnHm

detection: TIC

conversion to CO2

detection:TOC

detection:TOC

detection: TIC

conversion to CO2(3)

(4)(2)

(1)


Separation of total organic carbon (TOC) and total inorganic carbon (TIC)

Solid samples: Elemental Analysis

Flow chart summarizing analytical procedures to separate the sum parameters TOC und TIC from TC in samples containing organic compounds and carbonates


Separation of total TOC and TIC – Acid pretreatment [Bisutti, I. 2004, Brodie, C.R. 2011, Schlichting, E. 1995, chapter 5.5.4]


HCl in general used to quantify TIC in soils (DIN ISO 10693), as well as pretreatment agent for subsequent TOC measurements (DIN ISO 10694, DIN EN 13639), but also for sum parameter quantification of carbon in liquid samples (+) quantitative reaction with many carbonates (except siderite), variable in application (e.g. HCl concentration, techniques incl. time, temperature) (–) a) in situ-technique: possible overflow of material, CaCl2 and / or HCl residues in the sample containers, risk of hydrolysis and CaCl2-coating, high potential to damage components of analytical instruments (–) b) rinsing-technique: loss of soil organic matter (SOM), depending on acid concentration, heating (–) c) fumigation: like in situ-technique, and inefficient TIC removal H2SO3 used for soil treatment, particularly for sample pretreatment in δ 13C analysis as alternative to HCl (+) no or only small impact on SOM compared to HCl techniques (–) if heating is applied, decarboxylation can take place (–) not usable for samples containing dolomite or siderite, incomplete reaction (–) in situ-technique: overflow of material, hydrolysis, formation of SO2 during subsequent elemental analysis (–) can be a source of TOC contamination H3PO4 preferred in water analysis as alternative to HCl to remove inorganic carbon and to determine NPOC subsequently (DIN EN 1484:1997-08) (+) limits the risk of material damage, in soil analysis applied with heat (+) formation of sparingly soluble calcium phosphate can promote the reaction HNO3, H2SO4: not recommended, because of their oxidation potential; H2SO4 with FeSO4: FeSO4 is added to minimize oxidation and decarboxylation of organic matter HClO4: only for liquid samples. No heating! Otherwise oxidation of SOM, formation of perchlorates.


Separation of total TOC and TIC – Thermal pretreatment


Temperature [°C]200 300 400 500 600 700 800 900 1000

Rec

over

y ra

te o

f car

bon

[%]

-20

0

20

40

60

80

100

CalciteDolomite MagnesiteCelluloseWood Humic acid (peat)Humic acid (lignite)Coal (lignite)Coal (hard-coal)

Combustion and decomposition temperatures of different organic and inorganic carbon compounds [Bisutti, I. 2007]




sandy soils 550 °C for 4 hours arid zone soils 400 °C for 8 hours mineral soils 450 °C for 12 hours forest floor 450 °C for 12 hours different loams 450 °C for 4 hours sediments 450 +- 10 °C for 16 hours; 475 - 500 °C for 4-6 hours particulate carbon 500 °C for 4 hours

Examples for thermal pretreatment of solid samples [Bisutti, I. 2004]

samples temperature and time to remove TOC




TOC, directly, via HCl MethodCarbon content [%]

1.0 1.5 2.0 2.5 3.0

TOC

, ind

irect

ly, v

ia M

FMC

arbo

n co

nten

t [%

]

1.0

1.5

2.0

2.5

3.0

y = 0.9935 x + 0.0336r2 = 0.9983

Correlation between TOC determined directly (following DIN ISO 10694, HCl Method) and indirectly (Muffle Furnace Method, MFM) in samples from a calcareous soil profile containing < 4.5 % TIC in subsoil.




0 10 20 30 40 50 60 70 800

2

4

6

8

10

Car

bon

cont

ent [

%]

Soil depth [cm]

TOC, directly, via HCl MethodTOC, indirectly, via MFMTC, via Elemental AnalysisTIC, directly, via MFM

TIC, directly, via MFMCarbon content [%]

0 2 4 6 8 10

∆ TO

C(H

Cl M

etho

d - M

FM) /

HC

l Met

hod

[%]

0

20

40

60

80

∆ TOC = 0

TOC, TIC and TC from a calcareous soil profile with high TIC amounts.

Difference of TOC expressed as percentage in relation to TIC contents. Solid line represents the target: Δ TOC = 0; no deviation between the methods.

TOC is determined directly (following DIN ISO 10694, HCl Method) and indirectly (Muffle Furnace Method, MFM). Results derived from samples of a calcareous soil profile with high TIC amounts in subsoil. Solid line represents the target: Δ TOC = 0; no deviation between the methods.


Separation of total TOC and TIC – conclusion


Because the HCl Method can overestimate the TOC contents in soils containing higher amounts of carbonate (> 4 % TIC), the MFM should be applied as method of choice. The MFM provides reliable and precise results, although it needs two measurements for calculating the TOC: TOC = TC – TIC, compared to the HCl Method with a single, direct TOC determination. However, to test unknown samples, a reference method like an acid pretreatment should be used in addition in order to check whether the organic matter has been decomposed completely and to ensure that thermally instable carbonates are not present.

detailed description: General principles for the quantification of Total Organic Carbon (TOC) in environmental solid and liquid samples. I. Hilke https://www.bgc-jena.mpg.de/uploads/Publications/TechnicalReports/30_2015_TechnicalReport_Hilke.pdf


Liquid Samples: Sample Preparation

alteration of liquid samples: • microbial activities • oxidation caused by O2 from air • precipitation

stabilization / preservation: • physical methods and / or • chemical methods

sampling • exclusion of O2 • choice of the most suitable container material: glass? polyethylene? • storage: cool (2-5°C), dark, for longer periods: frozen (-18°C)

chemical methods change of the pH (addition of acids for cations, addition of NaOH for anions); other chemicals

physical methods particle filtration (< 0.45 µm), steril filtration (< 0.22 µm)

ref.: http://www.fachdokumente.lubw.baden-wuerttemberg.de/servlet/is/10115/s_26_LitStudieGW.pdf?command=downloadContent&filename=s_26_LitStudieGW.pdf&FIS=161


Liquid Samples: Sample Preparation chemical methods shift of the pH (e.g. addition of acids for cations, addition of NaOH for anions); addition of other chemicals

SO42-, Cl-, Br- g, pe 2 – 5 °C F - pe 2 – 5 °C NH 4+ g, pe 2 – 5 °C, dark, pH < 2 (+ H2SO4) NO2- g, pe 2 – 5 °C, instable, current amount: < 2 h S2O32- instable, NaOH, current amount: < 1 day

NO3- g, pe 2 – 5 °C, dark, pH > 10 (+ NaOH) PO43- g 2 – 5 °C TOC, DOC g 2 – 5 °C, dark, pH < 3 (+ HNO3 / HCl / H3PO4) Na+, K+ pe 2 – 5 °C Ca2+, Mg2+, Mn2+ pe pH < 2 (+ HNO3 suprapure)

parameter container stabilization g = glass, pe = polyethylene

ref.: http://www.fachdokumente.lubw.baden-wuerttemberg.de/servlet/is/10115/s_26_LitStudieGW.pdf?command=downloadContent&filename=s_26_LitStudieGW.pdf&FIS=161


Liquid Samples: Sum Parameter Carbon

TOC determination in liquid samples can be carried out in two ways: 1. directly 2. as difference 1. Direct Mode (TIC & NPOC), from one sample • the sample is automatically transferred into a special glass vessel (sparger), and a certain amount of HCl 1.6%

is added to remove TIC; the evolved CO2 is carried to the infrared (IR) detector and quantified • non-volatile carbon compounds remain in the sparger and are consecutively submitted to catalytic high-

temperature combustion at 1050 °C. The CO2 produced by combustion is, again, quantified by the IR detector. 2. Difference Mode (TIC & TC), from two aliquots of the sample • first aliquot TC ; total carbon is converted into CO2 by catalytic high-temperature combustion at 1050 °C

and quantified by the IR detector • second aliquot transferred into the sparger, automatically acidified with HCl 1.6 % to remove the TIC; the

evolved CO2 is carried to the IR detector and quantified. The TOC is finally calculated: TOC = TC - TIC


TC / DC; TOC / DOC; TIC / DIC; NPOC; VOC

TC = TOC + TIC TOC = NPOC + VOC TC = PC (<0.45µm) + DC (<0.45µm)

1) autosampler: with or without

purging

3) reaction: high temperature combustion

oxidation catalysts

2) separation: of inorganic and organic carbon

addition of acid

4) detection: of CO2

infrared spectroscopy


Liquid Samples: Sum Parameter Nitrogen

• 100 mL syringe injects a selectable sample volume (e.g. 30 µL] into a reaction tube which is filled with a platinum catalyst. The sample is combusted at 800 - 900°C in pure oxygen; the oxygen is used as carrier gas as well

• all bound nitrogen compounds in the sample are oxidized to NOX and converted subsequently into NO • an electrical dehumidifier eliminates the moistness from the resulting NO gas. • after this, NO reacts with ozon in the chemiluminiscence cell according to the following oxidation reaction: NO + O3 NO 2* + O2 NO2* NO 2 + hν

• a generally emitted wavelength of light (590-2500 nm) is possible during this reaction • the intensity of the emitted light is proportional to NO concentration • detection is carried out by a photomultiplier tube; for quantification the light is converted into an area value

after waveform processing


TNb; TN / DN; TON / DON; (TIN / DIN); Nmin TNb = Norg + Nmin TNb = Norg + NO3- + NO2- + NH4+

TN = PN (<0.45µm) + DN (<0.45µm)

1) autosampler: 2) reaction: high temperature combustion

O2, Pt

3) detection: of NO

chemiluminescence

TON = TN -TIN TNb = total bound N (without N2)


Liquid Samples: Automated Chemistry Analyzers

SFA, FIA, FIA/SFA Analyzes a wide range of concentrations: ppt, ppb, ppm, and percent. Accomodates on-line distillation, dialysis, digest extraction, and separation Discrete/Robotic New technology in environmental analysis with superior ease of use

What is FIA/SFA Technology? • FIA involves injecting small segments of sample solution into a flowing carrier stream. • The sample stream merges into the reagent stream to produce a compound that can be determined in a flow-through

detector, typically a photometric or amperometric detector. • SFA measures analyte quantities in a continuously flowing stream of sample or sample wash. • Bubbles injected consistently throughout the stream ensure complete mixing and minimize sample band dispersion. • FIA/SFA is the instrument that combines FIA and SFA processes into one system, gaining advantages from both

technologies.

What is a Discrete Automatic Chemistry Analyzer? • A discrete analyzer automatically adds sample and reagent to a small cell, i.e. cuvette. • It measures a reaction product while still in the cell or transfers it into a flow cell. It processes the sample in batches

or individually. • Key advantages include speed and use of only microliter amounts of sample and reagent. • It exactly mimics the operations of traditional manual wet chemistry methods.

ref.: Application Note 22350205, O-I Analytical, http://www.oico.com/default.aspx?id=appcenter


Liquid Samples: Automated Chemistry Analyzers

Advantages of Using Discrete Automatic Chemistry Analysis for Wet Chemistry Analysis • Much less sample volume than any other method, benefiting laboratories with small sample volumes (soil paste extracts) • Low reagent consumption (about 3,000 tests per 25 mL for the nitrite method); only uses the exact reagent amount required for each test compared to a continuously-flowing system; generates less waste • Automatic dilutions without added hardware • No baselines to watch, no air bubbles to add, no peak shapes or flows to monitor • No bubble formation in the flow cell • No pump tubes to change or maintain • Switch methods automatically without changing hardware • True “walk away” capability • Enormous improvements in setup, operational time, and ease of use • Stable calibration curves over long periods of time Disadvantages of Using Discrete Automatic Chemistry Analysis for Wet Chemistry Analysis • Presently, discrete analyzers can only do simple colorimetric chemistries • Cannot achieve ultralow detection limits • Time-consuming sample preparation steps such as distillations, digestions, and matrix removal or enhancement performed manually before testing by a discrete analyzer. • Cannot perform complex chemistries such as on-line gas diffusion, dialysis, distillations, extractions, and digestions

ref.: Application Note 22350205, O-I Analytical, http://www.oico.com/default.aspx?id=appcenter


Liquid Samples: Flow Injection Analysis

scheme FIA Quikchem



NH4+ – N:

Ammonia in Surface Water, Wastewater (Gas Diffusion) 0.05 to 5.00 mg N/L as NH3 – Principle –

– Interferences –

discussion in the lab



NO3- – N, NO2

- – N :

Nitrate and Nitrite in Surface Water, Wastewater 0.05 to 10.00 mg N/L as NO3 and NO2 Nitrite in Surface Water 0.004 – 0.400 mg N/L as NO2 – Principle – – Interferences –




PO43- – P

Orthophosphate in Waters, 0.01 to 2.00 mg P/L – Principle – – Interferences –




SO42-

Sulfate in Waters 1.0 to 50.0 mg SO42-/L – Principle – – Interferences –



Liquid Samples: Ion Chromatography

DX-500 - Anions

The Dionex DX-500 system is equipped with a gradient pumping module, a conductivity detector and an UV detector for the determination of fluoride, chloride, nitrate, nitrite, phosphate and sulphate in water samples and soil extracts (nitrate only). The sample is injected onto an ion-exchange column and eluted with a carbonate / bicarbonate buffer solution. Due to different retention times of the ions on the column, they are effectively separated and transported to the conductivity detector used in ion chromatography. It is possible to determine minute concentrations of nitrate in 1 M KCl extracts using an UV detector by a method developed in-house. The sample to be analyzed is spiked with 50 μL of a 50 ppm nitrate solution. This method is applicable in the range from 50 - 500 ppb nitrate.



ICS-5000 – Cations, “non-routine” Anions

The Dionex ICS-5000 system holds two IC cube modules, making dual channel analysis possible. The system is equipped with an eluent generator module using the benefits of an RFIC-EG (reagent free ion chromatography-eluent generation) in a dual system format, an pumping module holding two isocratic pumps, and a detector compartment with two conductivity detectors. For one of the both channels, an UV detector is additionally available. Via autosampler, the samples are injected onto the ion-exchange columns and eluted with a KOH solution in case of anions, and with MSA in case of cations. Due to different retention times of the ions on the column, they are effectively separated and transported to the detector compartment.



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