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Advanced Sample PreparationTechniques

G. KnappGraz University of Technology October 2004 1

Günter KnappInstitute for Analytical Chemistry and Radiochemistry

Graz University of TechnologyAustria

[email protected]

High Performance Sample Digestion


•Losses of elements ?•Contamination ?•Interferences with residual organic compounds ?

• Wet digestion– in closed pressurized vessels– in open pressurized vessel– with microwave boosted UV-lamps

• Combustion

Nitric Acid –Optimum Reagent for Wet Digestion


• Ultra pure after subboiling distillation

• Little interferences with subsequent measurement methods– Atomic absorption– ICP – OES– ICP – MS

Subboiling Distillation Apparatus


Teflon IR heated subboilingstill in class-100 clean air hoodwith leveling reservoirconstructed from modular Teflon PFA segments.

PFA Labware Catalog; Savillex Corp.: Minnetonka, MN, 1995

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Oxidation Efficiency ofPressure Decomposition with HNO3 (65%)

Ref.: P. Fecher, CLUA Erlangen, Germany

02468

1012

150 °C 200 °C 250 °C 300 °C

30%% C

Milk PowderCitrus LeavesFish TissueBovine LiverMargarine


Pine Needles Milk Powder Bovine Liver Polyethylene Crude Oil0

5

10

15

20

25

Pine Needles Milk Powder Bovine Liver Polyethylene Crude Oil

LP-Microwave HP-Microwave HPA-S

% C > 30 % , not mineralized X X

Oxidation Efficiency –Comparison of Commercial Equipments


High Temperature Wet Digestion (320°C)High Pressure Asher HPA-S

HPA-SAnton Paar, Graz, Austria; www.anton-paar.com/ap/


Wet Digestion at High TemperaturePressurized Digestion in Closed Vessels

Tem

pera

ture

[°C

]

240

220

200

180

160

140

Res

idua

l Car

bon

Con

tent

[%]

2,5

2,0

1,5

1,0

0,5

0,2 0,4 0,6 0,8 1,0 1,2Sample Weight [g]

Temp TOC

ptotal = pCO2 + pHNO3 + pNOx

pHNO3 ≈ T pCO2 ≈ sample weight &

vessel volumepmax depends on the

digestion system

Resultincreasing sample weightdecreasing digestion temperatureincreasing organic residue


Design of Pressure Vesselsfor Microwave Assisted Wet Digestion

SCREW FASTENED LID SPRING FASTENED LID PISTON TYPE LID

Coolingair

Stopper withrupture discand sealing

Screw cap

Digestionvessel

Vesseljacket

Screw

Spring

Adapterplate

Lid

Liner

Jacket

Rotor

Vent stem

Rupturedisc

Lid

Screw cap

Liner

Jacket

Cooling air

Simultaneous Pressure Measurement


M. Zischka, P. Kettisch, A. Schalk, G. Knapp; Fresenius J. Anal. Chem. 361 (1998) 90

decompositionvessel

vessel jacket

screw cap

lid

cooling air

cooling air

cooling airpiston


Simultaneous Pressure MeasurementRotor-System

M. Zischka, P. Kettisch, A. Schalk, G. Knapp; Fresenius J. Anal. Chem. 361 (1998) 90

1

2

3

45

67

8

9 9

1 pressure vessel2 vessel jacket3 piston type lid4 piston5 hydraulic fluid6 pressure transducer7 IR pressure signal8 Cooling air9 IR temperature signal


Simultaneous Pressure MeasurementRotor MULTIWAVE 3000Anton Paar, Graz, Austria; www.anton-paar.com/ap/


Simultaneous Pressure MeasurementMULTIWAVE 3000

Anton Paar, Graz, Austria; www.anton-paar.com/ap/


Multiwave 3000High Performance Sample Decomposition

Digestion of 0,3 g polyethylenewith 5 ml conc. nitric acidin a 80 ml quartz vesselat 250°C and 80 bar


Multiwave 3000High Safety Standards

Explosion of an overloaded vesselDigestion of 0.5 g polypropylenewith 5 ml conc. nitric acidin a 80 ml quartz vesselat 250°C and 80 bar


Wet Digestion at High TemperaturePressurized Digestion in Open Vessels

Advantage•Quasi infinite vessel volume

•Maximum possible temperature depends

only from applied pressure

•Simple digestion vessels



HPA-S®

(Anton Paar Comp., Graz, Austria)

1 Autoclave2 Lid of the autoclave3 Ring retainer4 Rupture disc5 PTFE liner6 Heating element7 Thermocouple8 Water bath9 Quartz vessel

10 PFA vessel11 PTFE lid for digestion vessel12 Vessel rack made of titanium

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B. Maichin, M. Zischka, G. Knapp; Pressurized Wet Digestion in Open Vessels, J. Anal. Bioanal. Chem. 2003 in press



HPA-S



Quatz Vessels50 mL

PFA Vessels25 mL

AutosamplerCups (PFA)

1.5 mL

Sampleamount 1.0 g 0.5 g 50 mg

Digestionmixture

5.0 mL HNO3 +0.2 mL HCl

5.0 mL HNO3 +0.2 mL HCl

0.2 mL HNO3 +0.5 mL H2O +0.2 mL H2O2



• Digested Materials:• Cocoa, pumkin seeds, lubrication oil, polyethylene, polypropylene,

bovine liver, sunflower oil,

• Digestion program• Linear temperature ramp up to 250°C (270°C) within 90 min.• Hold 250°C (270°C) 30 min. ( 270°C - temperature for quartz vessels)• Cooling time 30 min.

• Residual carbon content• 0.2 – 2.0 %



UltraClave(Milestone)

UV – Assisted Wet Digestion


M. Kolb, P. Rach, J. Schäfer, A. Wild; Fresenius J. Anal. Chem. 342 (1992) 341G. Schwedt, J. Petri; Labor Praxis (1992) 1223

• Advantages– Very low acid concentration– Low blank levels

• Disadvantages– Long digestion time– Only for aqueous samples with low organic content

UV – Assisted Wet Digestion


Quartz Vessel

Digestion Solution

UV - Lamp

Principle of the digestionapparatus.

Very low concentrationof HNO3 and H2O2


Microwave Assisted High TemperatureUV – Sample Digestion

Dieter Florian, Günter Knapp; Anal. Chem. 2001, 73, 1515-1520G. Knapp, US Pat. 6,210,538 B1; Apr. 2001

Microwaves as energy sourcefor simultaneous heating of the reaction mixtureand for generation of UV radiation.


Microwave Boosted UV-Reactorfor Photochemical Reactions

at High Temperatures

Microwave Assisted UV Digestionof Organic Substances at High Temperatures


Advantages of Microwave AssistedUV Digestion at High Temperatures


• Acceleration of the degradation process owing to high reaction temperature (250 – 280 °C)

• Best efficiency of generated UV-radiation (immersion system)

• Enhancement of reactivity due to simultaneous microwave and UV-irradiation

• Closed system and therefore low risk of systematic errors

Microwave Assisted UV Digestion –Procedure


Equipment for high pressure microwave digestion:Multiwave 3000 (Anton Paar Comp. / Perkin Elmer)80 mL quartz vessel

MWL: Low pressure Cd-discharge lamp (Anton Paar Comp.)

Sample materials:Phenylalanine, glycine, wheat flour, bovine liver

Procedure:50 – 100 mg sample + 7 mL H2O + 1 mL H2O2 + 0.05 mL HNO3vessel pressurized with 10 bar oxygen30 Min. at 80 bar (about 250°C)

Microwave Assisted UV Digestion –Results


Comparison of sample digestion with and without MWL

Sample material Sample weight Residual carbon[mg] [%]

with lamp without lamp

Phenylalanine 50 1,9 12,3

Glycine 50 0,9 19,5

Bovine liver 100 8,2 24,6

Wheat flour 100 0,9 5,3

Combustion Systems


Combustion of organic samples in closed systemsis state of the art for the determination

of volatile nonmetals.

Combustion Systems –Oxygen Bomb


a) Steel bombb) Lid with valvec) Electrodesd) Ignition wiree) Sample holder

Combustion Systems –Oxygen Bomb


• 500 mL steel combustion bomb from Parr Instr. USA.• About 0.5 g sample material is pressed into a tablet, which is placed in a cup made of

porcelain, platinum or silica.• The bomb is filled with 25 – 50 mL of absorption solution.• The bomb is closed with the lid and filled with oxygen to the required pressure

of 25 – 40 bar.• The sample is ignited electrically by means of an iron wire.• Time for absorption (the bomb must be shaken every 15 min.):

Cl-, Br-, J-, SO42- 1 hourF- 3 hours

• Absorption solution:Cl-, F- ion chromatography eluent (CO32- / HCO3-)Br-, J-, SO42- ion chromatography eluent (CO32- / HCO3-)

or diluted NaOH + 3 drops 30% H2O2

Combustion Systems –Microwave Assisted Sample Combustion


E.M. Flores, J.N. Paniz, J.S. Barin, J.A. Medeiros; Pat. Pen.

Combustion Systems –Microwave Assisted Sample Combustion


decompositionvessel

vessel jacket

screw cap

stopperwith rupture discand sealing

cooling air

cooling air

cooling air

sample

sample holder

• MULTIWAVE 3000• 80 mL quartz vessels• 0.3-0.4 g sample depending on the

organic material• Loaded with 20 bar oxygen• Ignited with microwave power

by means of impregnated filter paper• 8 combustions simultaneously• Absorption solution mobile phase

from ion chromatography• Absorption time 1 hour• IC for Cl-, Br-, I- and S (sulfate)• Ion selective electrode for F-

Microwave Assisted Sample CombustionResults


Cl S

certified measured certified measured

BCR 60Aquatic plant

10g / kg

9.3 ± 0.8g / kg

5.2g / kg

5.0 ± 0.4g / kg

BCR 61Aquatic plant

2.3g / kg

2.3 ± 0.3g / kg

2.3g / kg

2.1 ± 0.3g / kg

BCR 63Milk powder

9.94 ± 0,3g / kg

10.1 ± 1.0g / kg

BCR 100Peach leaves

1.49 ± 0.06g / kg

1.55 ± 0.1g / kg

2.69 ± 0.04g / kg

2.7 ± 0.1g / kg

BCR 186Pig kidney

9.4g / kg

9.5 ± 0.5g / kg

Microwave Assisted Sample CombustionDemonstration


• Combustion of 0.4 g Milkpowder

• MULTIWAVE 3000

• 80 mL Quartz vessel

• Loaded with 20 bar oxygen

Trends inSample Preparation

2006


July 02th – 05th, 2006Seggau-Castle / StyriaAUSTRIA

www.analytchem.TUGraz.at/acmr/en/events/2004

Trends inSample Preparation

2006


July 2th – 5th, 2006Seggau-Castle / Austriahttp://www.analytchem.tugraz.at/acmr/en/events/

Topics:

•Inorganic analysis:drying; homogenization; wet digestion; combustion; fusion; etc.

•Organic analysis:extraction; derivatization; etc.

•Speciation analysis:extraction; derivatization; etc.

•Microwave techniques for sample preparation;

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