Microwave Sample
Preparation
Sample Preparation Objectives
(AAS and AES)
The ideal sample preparation would do the following:
Convert solid and liquid samples to aqueous solutions
Destroy all organic matter
Retain all analytes of interest in solution at detectable
concentrations
Add no interfering ions
Adjust sample viscosity and solids to the optimum for
analysis
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Classical Digestion Approaches
Open Vessel on Hot Plate
• 전처리가 쉽다
• 비용이 저렴하다
• 처리속도가 느리다
• 수동적이다
• 오염이 쉽다
• 저온, 온도조절
. .. .
. .
.
Pressure Decomposition Vessel
Screw Cap
Seal
Vessel
Liner
Vent
Today’s analytical instrument places
demands on the chemist to choose a
sample preparation method which is:
신속성(Rapid)
정확성(Reproducible)
신뢰성(Reliable)
안전성(Safe)
Microwave Sample Preparation Techniques
AA 및 ICP분석을 위한
시료 분해
LC 및 GC용
용매추출
아미노산분석을 위한
펩타이드 및 단백질의
수소화
시료건조
GPC분석을 위한 고분자 희석
유기합성반응
고밀도 관학물질 및 건축자재 분해
회화
Why Microwave Decomposition?
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시료에 직접 에너지 전달 (heat is a by-product)
에너지 조절 = 분해조건 재현성
전통적인 방법 병행
신속함으로 저비용
정확한 분해가 가능
사용되는 산이 소량이다
휘발성물질 분해가 가능하다
저농도에서 오염이 적다
폐쇄형 용기 대기압 하에서 사용이 불가하며, 온도를
점차로 증가하여 사용
A Microwave

c
H

 = electric field
H = magnetic field
 = wavelength (12.2 cm for 2450 MHz)
c = speed of light (300,000 km/s)
X-Rays
Ultraviolet
Visible
Electromagnetic Spectrum
Infrared
Microwaves Radiowaves
Laser Radiation
10-10 10-9 10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
Wave Length (meters)
3x1012
3x1010
3x108
3x106
3x104
3x102
Frequency (MHz)
Inner-shell
electrons Outer-shell
(valence)
electrons
Molecular
vibrations
Molecular rotations
액체(mineral acids) 의 경우 마이크로
에너지가 노출되었을 때 빠르게
가열된다. 마이크로에너지는 다음 두
경우에 흡착이 일어난다.
Dipole Rotation(쌍극자 회전)
Ionic Conduction(이온의 유도작용)
Dipole Rotation쌍극자 회전)
Microwave Electric Field Interaction with Water Molecule
+
물분자의 쌍극자(dipole) 열적 혼잡도 유발(field
off)
0


H
O
물분자의 쌍극자(dipole) 필드상에서
정열 (field on).
+
Electric Field
H
0


O
H

H
+
0
물분자의 쌍극자 열적혼잡도 재
유발 (field off)



H
O
H
Schematic of Dipole Rotation in a Magnetic Field
+
H+ H+ H+ H+ H+ H+
-O -O -O -O -O -O
H+ H+ H+ H+ H+ H+
Field on
H+
-O
H+
H+
-O
Field off (thermally induced disorder)
H+
-
Ionic Conduction
- -- -+ -
Asymmetric
Effect
전자기장상에 전자구름 과 양이온 대칭
Electrophoretic
Effect
- -- - -- --+---- -- - ---+---- - - -- - - -- - - - --- ----- ---+---- -- --- -+- -- --
+
--+ --
전자기장에 이온구름이 존재
+
+
Solvated central ion moving against the crowd of solvated counter ions
Material Interaction With Microwaves
Reflective
Conductor
(전도체)
마이크로에너지 물질에 반사
가열안됨
Transparent
많은 물질은 마이크로 에너지를
투과하나 좋은 절연체를 사용하지
않으면 가열 안됨.
Insulator
(절연체)
Dielectric
(유전체)
. ....
.
Absorptive
마이크로 에너지가 물질에 흡착되어
가열
MARS 5X Cavity, Vessels and Exhaust System
Exhaust
Fan
Microwave
Cavity
Solvent
Detector
Extraction
Vessel
Air Flow
Switch
Sample Heating by Microwaves
Sample-acid mixture
(absorbs microwave
energy)
Liner, sleeve & frame
transparent to MW
energy
Gas
Vapor
Microwaves
Vessel Body
Liquid
Localized
superheating
Technologically Advanced Features
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1200 watts of microwave power
Continuous power at 300, 600 and 1200 watts
“Auto Load” power sensing
Variable Speed Stirring of all samples
Operates stand alone or Marslink PC Package
Solid Steel Flex & Seal Door with Window
Calibrated IR Sensor Monitors All Vessels
Power
Auto Load Sensing
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The appropriate continuos power level is
selected (300, 600, 1200 watts)
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Computer collects data from temperature
and pressure sensors
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Automatically adjust the output of the
magnetron within the power level selected
MARS Plus Control Vessel
RTP Plus and TempGuard Temperature Controls
Insitu Temperature
via EST Plus
External
Temperature via IR
Microwave
Controller Compares
External to Insitu
Measurement and
calibrates the IR
sensor once each 7
seconds
Temperature/Pressure Control System
Schematic for the MARS Series Units
MARS 5
VERSION 12345
COPYRIGHT
CEM CORPORATION
BACK
NEXT
SCREEN
HOME
SELECT
SETUP
PRINT
START
PAUSE
STOP
IR
Actual
RTP
Set
P P
Actual
Set
All Vessel Variable Speed Stirring
XP 1500 Plus Control Vessel
XP 1500 Plus Control Vessel
XP 1500 Plus Control Turntable
5
6
Guidelines for Method
Development
ORGANICS
Organic Materials
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Plant and Animal Tissue
Oil and Oily Waste
Paint and Paint Chips
Foods
Polymers
Graphite Resins Composites
Things to Consider……
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Acid Type
Sample Size
Vessels
Ramping control
Pre-Digestion
Char
Acids and Acid Mixtures Useful
for Oxidation
• Nitric Acid (70%)
• Nitric acid (70%) followed by Hydrogen
Peroxide (30%)
• Sulfuric Acid (98%)-Nitric Acid (70%)
followed by Hydrogen Peroxide
General Procedure for Digestion
of Organic Material
• Acid
Nitric Acid (70%)
• Acid Volume
10 - 15 mL
• Sample Size
< 0.5 gram dry weight
350
350
300
300
250
250
200
200
150
150
100
100
50
50
.25 gram
0
0
10
20
.36 gram
30 0
10
20
Time (min.)
.46 gram
30 0
10
20
Pressure (psig)
Temperature ( o C)
Conostan Oil Nitric Acid Digestion
Sample Size Pressure-Temperature Comparison
0
30
Pressure
Temperature
6 vessels
10 mL HNO3
MDS-2000, 620 watts
Choosing a Vessel for Organic
Digestions
• Low Pressure Vessel with multiple vent and
reseal steps.
• High Pressure Vessel with a single heating
step.
Predigestion
After adding acid to samples, allow vessels
to stand open in hood. This will allow the
gases from initial reactions to escape before
the vessel is capped.
Try a Char Step When...
• Digesting a sample that contains aromatic
rings
• It is necessary to digest large sample sizes
How to Char a Sample
• Add sample and 5-10 mL of Sulfuric Acid to XP1500 vessel and seal.
• Complete a program similar to the following.
After the Char Step…..
• Add 10-15 mL of Nitric Acid to the vessels
– Vessels must be cooled to room temperature
before addition of nitric acid. Acid must be
added carefully to charred sample
• Re-seal the vessel and complete a program
similar to the following.
Summary for Organic Samples
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유기물 분해시 초기에 질산 사용
유기물 분해시 최대 시료 0.5 gram (dry weight)
고압 vessel 사용
재 분해시 발열반응에 주의
시료 특성을 고려한 온도 프로그램 작성
Inorganic Materials
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Soils
Ores
Ceramics
Catalysts
Metal Alloys
Ash
Water
Things To Consider...
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Acids
Sample Matrix
Analytes of Interest
Heating Programs
Step-wise Approach
Troubleshooting and Methods
Development
Nitric Acid
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Oxidizing acid
Starting acid for organics
Most nitrates are soluble
Compatible with most analytical techniques
Can be obtained in high purity
May passivate certain metals (Al, Cr, Ti)
Hydrochloric Acid
• Complexing agent
• Forms soluble complexes with many
metal ions
• Not an oxidizing acid
• Useful for Fe, Al, In, Sb, Sn
• May interfere with GFAA and ICP/MS
Hydrofluoric Acid
• Dissolution of silicates (minerals, soils, botanicals)
• F- is a powerful complexing anion
(refractory elements)
• Volatilization of Si as SiF4
• Formation of insoluble fluorides
(Group IIA, Rare Earth elements)
• Complex with H3BO3
• Safety Hazard
• HF resistant transport systems for ICP/AA
Sulfuric Acid
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High boiling point (340°C)
Elevation of boiling point in acid mixtures
Strong dehydrating agent
Char step
Low volatility of metal sulfates
Formation of insoluble sulfates
High viscosity may cause analytical
problems
Acid Mixtures
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HCl:HNO3 (3:1) Precious metals
HNO3:H2SO4 High molecular wt. organics
HNO3:HCl:HF Alloys, ores, silicates, ash
H3PO4:H2SO4 Aluminum oxide
Soils and Sediments
• Leaching
– EPA 3051 HNO3
– EPA 3051a HNO3, HCl
• Complete Digestion
– EPA 3052 HNO3, HF
(HCl, H2O2, H2O, and H3BO3may also be added)
• High carbon content: may need pretreatment with
HNO3
• H3BO3 may be required to solubilize Group IIA
and Rare Earth fluorides
Ceramics and Catalysts
• Determine the matrix
• H3PO4:H2SO4 or HCl for Al2O3
HF for SiO2
• Step-wise approach
• Particle size is very important
Sample: Mullite
Al2O3 : SiO2 (3:2)
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Sample Preparation: Reduce particle size
Acids: H3PO4 and HF
Sample Size: 0.1 g
Digestion Approach: 2 Steps
– H3PO4 (digestion of Al2O3)
– HF (digestion of SiO2)
Water
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EPA 3015
(HNO3)
EPA 3015a (HNO3, HCl)
NPDES
(HNO3, HCl)
Beware of dissolved organics
– Alcohols
– Glycols
– Amines