Supplemental Information
Pyroelectricity
Assisted
Infrared-Laser
Desorption
Ionization
(PAI-LDI)
for
Atmospheric Pressure Mass Spectrometry
Yanyan Li,1 Xiaoxiao Ma,2 Zhenwei Wei,1 Xiaoyun Gong,1 Chengdui Yang,1 Sichun Zhang,1*
Xinrong Zhang1
1
Department of Chemistry, Beijing Key Laboratory for Microanalytical Methods and
Instrumentation, Tsinghua University, Beijing, 100084, P. R. China
2
Department of Chemistry, Purdue University, West Lafayette, IN 47907-2084, United States
Address reprint requests to: Sichun Zhang
Address: Department of Chemistry, Beijing Key Laboratory for Microanalytical Methods and
Instrumentation, Tsinghua University, Beijing, 100084, P. R. China
Tel: +086-10-62787678
Fax: +086-10-62782485
E-mail: sczhang@mail.tsinghua.edu.cn
1
Supplemental Information
1. Information of Materials and Chemicals.
Table S1. Standard Compounds Information for method establishment
Mark
Sample
Number name
S1
1-Acetamidoadaman
tane
Molecula Structure
r weight formula
193.29
CAS
number
880-524
Compoun
d type
Amide
S2
Acetanilide
135.16
103-844
Amide
S3
2-Aminopyrimidine
95.10
109-126
Amine
S4
1-Adamantylamine
151.25
768-945
Amine
S5
Spermine
202.34
71-44-3
Aliphatic
Diamine
S6
2-Aminobenzamide
136.15
88-68-6
Aromatic
Amide
2
Table S2. Saccharide Substances Information
Mark
number
S7
Sample name
S8
D-(+)-Maltose·H2O 360.31
69-79-4
S9
Maltotriose
1109-28-0
D-(+)-Glucose
Molecular
weight
180.16
Structure formula
CAS
number
50-99-7
504.44
Table S3. Substrates Material Information
Category
Substrate
Dimensions (L×W×H)
Functional Materials Lithium Niobate (LiNbO3) 15.0 mm×15.0 mm×0.5 mm
Metal
Copper (Cu)
15.0 mm×15.0 mm×0.2 mm
Organic Materials
Quantitative Filter Paper
([C6H10O5]n)
15.0 mm×15.0 mm×0.05 mm
Inorganic Salt
Microslide
(Borosilicate Glass)
25.4 mm×76.2 mm×1.0 mm
Table S4. Property about Lithium Niobate (LiNbO3) (Reference: PubChem and Ref 13 in
manuscript)
Property
Parameter value
Property
Parameter value
Molecular
LiNbO3
Functional
Pyroelectricity,
performance
Piezoelectricity etc.
PubChem
159404
Molecular weight 147.8456g/mol
Pyroelectric coefficient
70μC/(m2 K)
Crystal orientation z-cut
Crystal
Fine grinding
Melting point
1255±5℃
Curie temerature
1140±5℃
Density
4.644g/cm3 @20℃ Thermal conducitivity
Moh’s hardness
~5
formula
CAS number
12031-63-9
4.0W/m/K@25℃
Refractive indices@1064nmno=2.232
3
2. Complement for Mass Spectra
Figure S1.Mass spectra of mixed compounds obtained on different substrates
The mixed solution included three compounds: 2-aminopyrimidine ([M+H]+, 96.1),
1-acetamidoadamantane ([M+H]+, 194.3) and acetanilide ([M+H]+, 136.2).
Figure S2.PAI-LDI Mass spectra of standard saccharide substances on LiNbO3substrate
a, D-(+)-Glucose; b, D-(+)-Maltose·H2O; c, Maltotriose. The mass spectra were used to assist
in components identification of Onion juice.
4
Figures S3. The mass spectrum of urine sample showing the whole mass range including
spiked 1-adamantylamine and urine native creatinine
Figures S4. The mass spectra of analyte using different pyroelectric material as the substrate
of PAI-LDI
3. The explanation of parameters selection for the ion source.
The distance between the sample spot center and MS inlet have been optimized. The
distance of ~10mm, 8mm, 6mm were respectively examined in preliminary experiments. We
found that ~6mm was the most appropriate distance. Higher than ~6mm causes the decrease
on the MS signals. Lower than ~6mm was not examined because there was no enough free
space for laser focus adjustment, due to our instrumental structure limitation. Therefore
~6mm was selected as the distance from sample spot center to MS inlet in following
experiments. Laser wavelength was 1064 nm, which is commercial available with fixed
single wavelength. The laser frequency was also commercial available equipped with four
variable values including 10Hz, 20Hz, 30Hz, 40Hz, which were respectively examined in our
preliminary experiments. We found that 20Hz was the most appropriate frequency. Higher or
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lower than 20Hz would cause decrease on the MS signals, especially, higher than 20Hz
would seriously damage pyroelectric substrate. The ~45° incidence angle to the distal end of
MS orifice was selected to maximize introduction of ions into MS orifice as well, which is
consistent with existing studies [1,2]. The distance from laser facula to sample spot center
was about 2mm.
We examined the effect of incident angle on MS response. The incident angle of 45
degree was used in this study, although the critical angel at the air/LiNbO3 interface is 27
degrees, as a result there should be laser energy loss due to reflection if a 45 degrees angle
was used. However, currently consideration, based on our equipment conditions, there was a
little difficult for laser device to combine with MS orifice at 27 degrees. According to our
experiments results, 45 degrees gives acceptable desorption/ionization efficiency and
detection sensitivity. At the same time, negative pressure near the MS orifice region plays a
role to facilitate transfer of analyte ions into MS, which would make the analysis insensitive
to the incident angle of the laser.
The distance from laser incidence to analyte spot center was within ~2 mm, which was
selected to make sure that analyte was efficiently desorbed and more ions were transferred to
MS orifice. The radius of sample spot was ~2 mm, when the laser incidence was located to
the periphery of the sample spot, thus from laser facula to sample spot center was ~2 mm.
However, the laser radiation hit the sample spot. Probably due to the coffee-ring effect [3], in
the preliminary experiments, we found that the MS signals of analytes were relatively higher
when the laser incidence was directed to the periphery of the sample spot than to the center of
sample spot. To accurately quantify, multiple points of the sample spot would be radiated by
laser and the MS signals were taken average. For imaging, experiment manipulation was
scanning the whole sample spot, thus, the image result would not be affected by the distance
between laser incidence and sample spot center.
4. Table S5. Comparing PAI-LDI to other IR-LDI methods
IR-LDI
IR-laser
wavelength
Extra
Main analyte
ionizationassisted setup
PAI-LDI
1064nm
No
LAESI
2.94μm
ESI ion source Reserpine,
Verapamil
Amine,amide,
oligosaccharides
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Concentration/
or LOD
Volume of
sample
~132fmol
or (estimated
LOD) 27fmol
25fmol
8fmol
1.5-2μL
5μL
IR-LADESI
2.94μm
ESI ion source Bovine cytochrome
c,
Ibuprofen
Acetaminophen
ESI ion source bovine ubiquitin,
or high voltage bovine myoglobin
ESI ion source Myoglobin
Human blood
Ink molecule
DART ion
Dyestuff molecules
source
2nmol
2×10-5M
20mg/mL
~100μM
IR-LDESI
10.6μm
LIAD-ESI
1064nm
PAMLDI-MS
1064nm
HALDI-MS
1064nm
High voltage
AP-IR-MALDI[4] 2.94μm
Matrix and
high voltage
Peptide,ODN,
Ibuprofen
Lipid
1-3μL
30mg/mL-1
10μM
25μM
10-5M
1μL
10μL
6mg/mL
100μL
5. LOD estimation based on the PAI-LDI response to 1-adamanylamine
1-adamantylamine (Amantadine) was successfully detected based on PAI-LDI-MS at as low as
20pg (132.2fmol) (see figure 4a), where the S/N ratio was ~15, which was much higher than value of
three.
Considering the LOD defined as 3×standard deviation of the blank (approximately
corresponding to S/N ratio of ~3). Therefore we estimate the LOD based on PAI-LDI response to
1-adamantylamine
was
~4pg
(26.4fmol),
which
is
corresponding
to
other
laser
desorption/post-ionization techniques at same order of magnitude.
References:
1.
Zhang, J., Li, Z., Zhang, C., Feng, B., Zhou, Z., Bai, Y., Liu, H.: Graphite-coated paper as substrate for high
sensitivity analysis in ambient surface-assisted laser desorption/ionization mass spectrometry. Anal Chem. 84,
3296-3301 (2012)
2.
Ren, X., Liu, J., Zhang, C., Luo, H.: Direct analysis of samples under ambient condition by
high-voltage-assisted laser desorption ionization mass spectrometry in both positive and negative ion mode.
Rapid Commun Mass Spectrom. 27, 613-620 (2013)
3.
Hu, J. B., Chen, Y. C., Urban, P. L.: Coffee-ring effects in laser desorption/ionization mass spectrometry.
Analytica Chimica Acta. 766, 77-82 (2013)
4.
Shrestha, B., Nemes, P., Nazarian, J., Hathout, Y., Hoffman, E. P., Vertes, A.: Direct analysis of lipids and
small metabolites in mouse brain tissue by AP IR-MALDI and reactive LAESI mass spectrometry. The Analyst.
135, 751 (2010)
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