Speciation of Individual Mineral Particles of Micrometer Size by the ...

Speciation of Individual Mineral Particles of
Micrometer Size by the Combined Use of ATR-FT-IR
Imaging and Quantitative ED-EPMA Techniques
Md Abdul Malek, Hae-Jin Jung, JiYeon Ryu, BoHwa Kim,
Young-Chul Song, HyeKyeong Kim, and Chul-Un Ro *
Department of Chemistry
Inha University, KOREA

Airborne mineral dust particles
Airborne mineral dust - the most abundant PM in coarse atmospheric aerosols
Silicate minerals constitute ~90% of the Earth crust.
Mineral dust plays multiple roles in influencing global climate (e.g., scattering and
absorbing radiations, CCN).
Heterogeneous chemical reactions can also alter the chemical balance of the
atmosphere.
Hygroscopic property of mineral dust can change their reactivity.
Arid and semi-arid areas of the Saharan desert and central China are the global
scale sources.

Characterization of standard soil minerals
Airborne mineral particles – from soil minerals
Soil minerals rarely exist in a single-phase, pure mineral form.
Bulk FT-IR technique is a common practice for mineral analysis.
Bulk analysis - not sufficient for the speciation of mixed minerals
Analysis on a single-particle level can more clearly identify different mineral types.
The combined use of ATR-FT-IR imaging and quantitative low-Z particle EPMA
techniques gives complementary information
low-Z particle EPMA on the morphology and elemental concentrations
ATR-FT-IR imaging on mineral types
The combined use of these two single-particle analytical techniques has great
potential for the characterization of airborne mineral dust particles.

Low-Z particle EPMA (Electron Probe X-ray
Microanalysis) for single particle analysis
1. SEM-EDX (Scanning Electron Microscopy –
Energy Dispersive X-ray Spectrometer)
- Individual Particle Analysis
* shape and size : secondary / backscattered electron images
* chemical compositions : X-ray spectrum
2. Ultra-thin window EDX for low-Z elements detection (e.g., C, N, O, F)
3. Metallic collecting substrates for minimizing charging effect (e.g., Ag, Al)
4. Monte Carlo calculation for Quantification
5. Chemical speciation of aerosol particles – Expert System

Monte Carlo Calculation for Quantification
Measurement
Simulation
Electron detector
Electron beam
with 10keV
X-ray detector
1000
100
C
O
Ca
CaCO3 measured data
Simulated
SEM
metal foil
Intensity(arb. units)
10
1
0.1
0.01
0 1 2 3 4 5 6 7 8 9 10
X-ray Energy (keV)
Measured and simulated spectra for a
CaCO 3
standard particle on a Be substrate

ATR-FT-IR imaging for single particle analysis
♦ ATR-FT-IR (Attenuated Total Reflectance-FT-IR Spectrometry)
- Individual Particle Analysis
* location : optical image
* functional groups, molecular species, and crystal structure : IR spectra
Dual detector
Visible radiation
d = 600 μm
▲ ATR imaging accessory
Cassegrain system
Motorized sample stage
Ge crystal – sample contact surface ▲
sample
IR radiation
◄ Ge crystal for imaging

ATR-FT-IR Imaging for Single Particle Analysis

ATR-FT-IR and XRD measurements of minerals
ATR-FT-IR measurement
Perkin Elmer Spectrum 100 FT-IR spectrometer
Spectrum Spotlight 400 FT-IR optical microscope
ATR accessory: Ge IRE crystal, diam. = 600 μm, RI = 4
A 16 x 1 pixel Mercury Cadmium Telluride (MCT) array detector
Pixel size of 1.56 μm
Spectral resolution of 4 cm -1 at the range of 720 to 4000 cm -1
Spatial resolution 3.9±0.5 µm at 1000 – 1200 cm -1
XRD measurement
Philips X’pert MPD powder X-ray diffractometer
Cu Kα radiation
Scanning range of 2θ is 3-65 o
scanning speed is 0.02 o /s, a step size of 2θ is 0.02 o

Major minerals obtained by XRD for 24 mineral samples
Major mineral types by XRD Number of samples Source of sample
microcline (K-feldspar) 2 NIST, KIGAM
muscovite 4 KIGAM
montmorillonite 2 KIGAM
kaolinite 3 KIGAM
talc 2 KIGAM
heulandite 1 KIGAM
biotite 1 KIGAM
Mg-vermiculite 1 KIGAM
pyrophyllite 1 KIGAM
cristobalite (SiO 2
) 1 KIGAM
quartz (SiO 2
) 1 Aldrich
apatite 1 Aldrich
calcite 1 Aldrich
gypsum 1 Aldrich
anhydrous CaSO 4
1 Aldrich
magnesiumhydroxycarbonate hydrate 1 Aldrich
Total 24
NIST : National Institute of Standards and Technology, USA
KIGAM : Korea Institute of Geoscience and Mineral Resources

1500
1200
*
Major
* microcline (K-feldspar (KAlSi 3 O 8 ) )
XRD spectrum of K-feldspar
NIST SRM mineral sample.
counts/s
900
600
Minors
▼albite (Na-feldspar (NaAlSi 3 O 8 ) )
◊quartz (SiO 2 )
counts/s
300
0
* * *
*
▼▼* **
◊*
*
*
* *
*
* * * *
0 5 10 15 20 25 30 35 40 45 50 55 60
▼
65
▼▼
1200
1000
800
600
400
200
0
+ +
*
*
↓
◊↓
+▼
2θ
***
*
▼▼▼ *▼
▼ ▼▼▼ ▼ ♦ ◊
0 5 10 15 20 25 30 35 40 45 50 55 60 65
2θ
Majors
▼muscovite (KAl 2 (Si 3 Al)O 10 (OH,F) 2 )
* quartz (SiO 2 )
Minors
+ montmorillonite
((0.5Ca,Na) 0.7 (Al,Mg,Fe) 4 [(Si,Al) 8 O 20 ]
(OH) 4. nH 2 O)
♦albite (Na-feldspar (NaAlSi 3 O 8 ))
↓ orthoclase (K-feldspar (KAlSi 3 O 8 ))
◊kaolinite (Al 2 Si 2 O 5 (OH) 4 )
* *
*
*
*
*
*
*
*
XRD spectrum of a mineral
sample of muscovite and
quartz.

SE images (A) before and (B) after ATR-FT-IR measurement and ATR-FT-IR images
obtained (C) by a PCA analysis and (D) for transmittance signal at 1000 cm -1
(K-feldspar SRM mineral on Ag foil)
(A)
4
5 6
7
1 2 3
(B)
4 5
6
(1) 1 2 3
7
8
14 15
9 10
11
12 13
16
8
14 15
9 10
11
12
13
16
20
21
22
23 24
17 18 19
26
28
27
Δ
20
21
Δ Δ
22
23 24
17
26
28
18
27
19
1
3
25
29
25
29
(C)
4
20
21
1 2 3
5 6 7
8
9 10
11
12 13
14 15
16
17
18
22
19
27
23 24 26 28
25
29
(D)
4 5 6
20
21
8
22
7
1 2 3
9
10
11
12 13
14 15 16
23
24
17
25
26
28
18
27
29
19

Typical X-ray spectra and elemental concentrations of different feldspars
observed in K-feldspar SRM mineral sample
Intensity
1000
100
(A)
C
O
Al
Si
K
Ag
particle #5 (K-feldspar)
Diameter: 5.46 µm
Elemental concentration in at. %
C 3.8 O 54.0
Al 8.5 Si 26.2
K 7.5
1000
100
Intensity
(B)
C
O
Na Al Si
Ag
particle #2 (Na-feldspar)
Diameter: 3.63 µm
Elemental concentration in at. %
C 3.5 O 50.8
Na 8.2 Al 9.5
Si 28.0
10
10
Intensity
1
1000
100
10
0 1 2 3 4 5 6 7 8 9 10
keV
(C)
C
O
Na
Al
Si
Ag
K
particle #22 ((Na, K)-feldspar)
Diameter: 2.2 µm
Elemental concentration in at. %
C 1.0 O 57.6
Na 2.9 Al 9.0
Si 25.6 K 3.9
Intensity
1
1000
100
10
0 1 2 3 4 5 6 7 8 9 10
keV
(D)
C
O
Fe
Si
Al
Ag
K
particle #9 ((K, Fe)-feldspar)
Diameter: 1.79 µm
Elemental concentration in at. %
C 2.1 O 51.4
Al 15.0 Si 23.7
K 4.4 Fe 3.4
Fe
1
0 1 2 3 4 5 6 7 8 9 10
keV
1
0 1 2 3 4 5 6 7 8 9 10
keV

Typical ATR-FT-IR spectra of different feldspars observed in K-feldspar SRM mineral
sample.
(Conventional transmission FT-IR spectra of K- and Na-feldspar bulk samples reported
by the other study and an ATR-FT-IR spectrum obtained from bulk K-feldspar SRM
mineral powder are also shown in an inset.)
A
0.32
0.28
0.24
0.2
0.16
A
1
0.8
0.6
0.4
0.2
0
1720
transmission FT-IR
spectrum of Na-feldspar
transmission FT-IR
spectrum of K-feldspar
1520
1145:Si-O
1163:Si-O
ATR-FT-IR spectrum
of K-feldspar SRM Mineral
1320
1047:Si(Al)-O
1109: Si-O
1144
1120
1058
995
1018
1133
1088
1018:Si(Al)-O
1001:Si(Al)-O
1048
920
Matteson et. al., J. Sediment.
Petrol. 1993, 63, 1144-1148
760: Si-Si
788: Si-Si 747: Si-(Al)Si
725: Si-(Al)Si
775 735
725
769
720
1037:Si(Al)-O
1039:Si(Al)-O
1133: Si-O
1116:Si-O
1133:Si-O
1003:Si(Al)-O
1016:Si(Al)-O
770: Si-Si
729:
Si-(Al)Si
0.12
0.08
wavenumber, cm -1
particle #5 (K-feldspar)
particle #22 ((Na, K)-feldspar)
1153
1029
1097 1130
1002
774
732
0.04
0
particle #2 (Na-feldspar)
particle #9 ((K, Fe)-feldspar)
1126
1021
762
788
809
760
744
727
3720
3220
2720
2220
1720
1220
720
wavenumber, cm -1

SEIs SEM (A) before and (B) after ATR-FT-IR measurement and ATR-FT-IR images obtained (C) by a
PCA analysis and (D) for transmittance signal at 1030 cm -1 of a muscovite mineral sample on Ag foil.
(A)
12
14*
13
20
1
14
22
4
21
5
9
15
2
16
6
7
8
3
10
17
11
24
18
19
23
(B)
1 (K-F)
4 (K-F)
2 (MUS)
5 (Q)
6 (K-F)
3 (MON)
7 (MUS)
8 (Na-F)
9 (Q)
12 (MON)
10 (MUS)
13 (Q)
11 (MUS)
16 (MON)
18 (MON)
15 (K-F)
14 (K-F)
17 (MUS)
19 (Q)
20*
21 (Na-F)
14* (MON)
23 (Q)
22 (K-F)
*
24 (KAO)
(C)
1
4
12
13
14
14*
20
22
21
2
6
3
5
7
8
9 10
15
16
17
11
18
19
24
23
(D)
12
14*
2
1
6
4 5
8
3
7
13
9 10
16
17
15
14
*20
21
22
11
18
19
24
23
* (MON: montmorillonite, MUS: muscovite, Q: quartz, Na-F: albite, K-F: orthoclase (K-feldspar), KAO: kaolinite)

Typical X-ray spectra and elemental concentrations of different minerals
observed in a muscovite sample.
10000
1000
Intensity
100
10
(A)
C
O
Si
Al
Ag
K
particle #1 (K-feldspar)
Diameter: 3.85 µm
Elemental concentration in at. %
C 1.9 O 46.4
Al 11.5 Si 30.8
K 8.8
Intensity
10000
1000
C
100
10
(B)
O
Al Si
Mg
Ag
K
particle #2 (muscovite)
Diameter: 4.4 µm
Elemental concentration in at. %
C 3.6 O 59.6 Mg 0.5
Al 14.8 Si 17.8 K 1.5
Fe 2.1
Fe
Intensity
1
10000
1000
100
0 1 2 3 4 5 6 7 8 9 10
keV
(C)
C
O
Al Si
Mg
Ag
particle #3 (montmorillonite)
Diameter: 2.06 µm
Elemental concentration in at. %
C 4.6 O 60.2 Mg 1.4
Al 13.3 Si 17.8 Fe 2.7
Intensity
1
0 1 2 3 4 5 6 7 8 9 10
10000
keV
1000
100
(D)
C
O
Al
Si
Ag
particle #13 (quartz)
Diameter: 4.4 µm
Elemental concentration in at. %
C 1.2 O 62.8
Al 0.6 Si 35.4
10
Fe
10
Intensity
10000
1000
1
0 1 2 3 4 5 6 7 8 9 10
100
10
(E)
C
O Si
Al
Na
Ag
keV
particle #21 (Na-feldspar)
Diameter: 2.61 µm
Elemental concentration in at. %
C 2.9 O 50.8
Na 5.8 Al 11.4
Si 29.27
Intensity
1
10000
0 1 2 3 4 5 6 7 8 9 10
keV
1000
100
10
(F)
C
O
Al Si
Mg
Ag
particle #24 (kaolinite)
Diameter: 3.82 µm
Elemental concentration in at. %
C 0.5 O 60.9 Mg 1.2
Al 14.8 Si 20.0 Fe 2.6
Fe
1
0 1 2 3 4 5 6 7 8 9 10
keV
1
0 1 2 3 4 5 6 7 8 9 10
keV

Typical ATR-FT-IR spectra of different minerals observed in a muscovite mineral sample.
(An ATR-FT-IR spectrum obtained from bulk powder of this sample is also shown in an
inset.)
% T
100
90
80
70
60
50
40
30
20
10
0
% T
100
85
70
55
40
25
3687 3646
3626
3620
3695: -OH
3620: -OH
3720
3220
2720 2220
wavenumber, cm -1
1638: H 2 O
997: Si-O (MON, KAO, MUS)
Si(Al)-O (feldspar)
1720
particle #21 (Na-feldspar)
particle #1 (K-feldspar)
particle #24 (kaolinite)
particle #3 (montmorillonite)
particle #2 (muscovite)
particle #13 (quartz)
1220
795 & 777:
Si-O (Q, KAO); Si-Si (feldspar)
908: AlAl-OH (MON, KAO, MUS)
720
1651
1646
1653
1454
1456
1161
1163: Si-O
1046: Si-O
1135
1089
1034
988
1097
102
989: Si-O
994
999
998
913
917
917: AlAl-OH
782
778
755
791
825
756
824
720
721
747
755
747
775: Si-O
793: Si-O
3720
3220
2720
2220
1720
1220
720
wavenumber, cm -1
* (MON: montmorillonite, MUS: muscovite, KAO: kaolinite, Q: quartz)

Summary
Total samples analyzed: 24
Data presented herein: 2 samples
K-feldspar SRM sample
According to NIST specification, K-feldspar SRM sample consists of 80~85 % microcline, and 10~15 % albite
Based on X-ray and ATR-FT-IR spectral data of 29 individual particles,
15 particles were identified as K-feldspar
5 particles as Na-feldspar
8 particles as (Na,K)-feldspar, and 1 particle as (K,Fe)-feldspar
Muscovite and quartz sample
For the muscovite and quartz sample, among 24 individual particles
6 particles are observed as muscovite 5 particles as quartz
5 particles as K-feldspar 5 particles as montmorillonite
2 particles as Na-feldspar 1 particle as kaolinite
Different types of minerals were observed in the remaining 22 samples except samples
collected from Aldrich
A manuscript was submitted to Anal. Chem., where data for 22 mineral samples can be found.
Soil samples collected from various arid areas in China, and ambient aerosol samples
are under investigation.

Conclusions
The combined use of ATR-FT-IR imaging and low-Z particle EPMA
allows unambiguous identification of different minerals.
ATR-FT-IR imaging provides information on molecular and crystal
structure, functional group, and physical state.
Low-Z particle EPMA gives information on morphology and quantitative elemental
concentrations.
Analysis on single particle basis gives more detailed information than
bulk analysis.
It has great potential in elucidating the characteristics of soil-derived individual
airborne particles.
Our future project is to build up a good archive of mineral’s FT-IR spectra
for the facile assignment of soil-derived individual airborne particles.
(For low-Z particle EPMA, a library building is not necessary for X-ray spectra,
which is an advantage over FT-IR technique.)