Application of Laser Multi-Photon Ionization to Trace Detection in Chromatography
1
Application of Laser Multi- Photon Ionization to Trace Detection in Chromatography Victoria Fun-Young, Iris Litani-Barzilai, Valery Bulatov, Vladimir V. Gridin, and Israel Schechter Department of Chemistry, Technion - Israel Institute of Technology, Haifa 32000, Israel ABSTRACT Multi-photon ionization (MPI) has the potential to provide sensitive detection of a large variety of organic compounds. Coupling this technique with chromatographic methods, such as TLC and HPLC, may result in powerful analytical tools. Moreover, enhanced performance is expected when applying the resonant multi-photon ionization mode of operation. We examined the feasibility of utilizing MPI in conjunction with TLC and HPLC. The fast-conductivity method was applied, such that direct results can be obtained under ambient conditions. In particular, we focused on detection of polycyclic aromatic hydrocarbon mixtures, whereby direct MPI scanning of TLC plates were examined. HPLC detection The target The separation in Thin-Layer Chromatography is commonly observed by fluorescence or optical reflection data. The detection of non-fluorescent and/or colorless compounds is more difficult and uncertain. We suggest an alternative detection scheme, based upon the Laser induced Multiphoton Ionization (MPI) processes. Imaging Fluorescence (UV Absorbance) Detection PAH mixture solutio n TLC (HPLC) Analysis Multiphoton Ionization Fast Conductance Detection Figure 1 2 MPI-chromatogram obtained for n-hexane solutions of (a) pyrene, (b) 1-Brom-Pyrene and (c) their 1:1 mixture. Developed on Silica gel 60 precoated TLC plates by Cyclohexane for 20 min. 20000 40000 60000 80000 100000 120000 140000 160000 180000 19 21 23 distance from start,m m M PI Sign al, m V *m ksec 20000 40000 60000 80000 100000 120000 140000 160000 25 27 29 31 33 distance from start,m m M PISignal,m V *m ksec Figure 3a Figure 3b Br Experimental setup Single-trace TLC analysis Mixture separation/TLC The mixture of Benzo(e)pyrene (I), Pyrene (II) and 1- Bromopyrene (III) in n-hexane 1:1:1 was developed by cyclohexane for 25 minutes. The green line presents the fluorescence intensity along the TLC plate, obtained at 254 nm. The yellow line shows the corresponding MPI signals. Observe reliable MPI detection associated with each TLC spot-location. A simple and low cost fast-conductance technique (Fig. 2a) provides a photocurrent read-out due to the Multi-Photon Ionization of trace (Fig. 2b). -0.00 02 0.0000 0 .00 0 2 0 .00 0 4 0 .00 0 6 0 .00 0 8 0.0010 -4 -3 -2 -1 0 1 P hotocurrent/A rb.U nits Tim e /sec B enzo[e]pyrene Figure 2b Current Amplifier Storage Oscilloscope _ Power Supply + Nd-YAG 3 rd harmonic 355 nm XY- stage for TLC plate Figure 2a The same as in Fig. 4 but for a shorter (20 min) TLC development time. The MPI signal of pyrene is strong and readily observed. This demonstrates the situation where a poor fluorescing material can be detected by the MPI facility. Observe, however, that the MPI based separation of pyrene (II) and 1-Bromopyrene (III), seems incomplete. This is a result of the lower development time, since the “tale” of 1-Bromopyrene contributes to the MPI reading of the pyrene spot. benzo(e)pyrene, as a function of elution time. The HPLC results are cross- referenced with the corresponding MPI data obtained from the filter substrates. Conclusions In order to apply the MPI detection in HPLC, the effluent was transferred to glass fiber filters and the corresponding MPI-FC readings were recorded. 3.6 3.7 3.8 3.9 4.0 0 5 10 15 20 25 HPLC Absorbance /arb.units T im e /m in 3.6 3.7 3.8 3.9 4.0 0 2 4 6 8 10 12 14 M PIsignal, m V* s M PI Figure 6 Note the remarkable correspondence of the time-resolved HPLC read-outs to the MPI-FC photocharges. The molecular selectivity of the MPI detection (in its resonant mode) is exemplified: benzo(e)pyrene is resonatively ionized at 337 nm, while perylene is not. This results in huge differences in the slopes. 0 20000 40000 60000 80000 100000 120000 140000 160000 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 distan ce from start,m m M PISignal,m V*m ksec/ fluorescence intensity,arb.units Figure 4 II I I II Multi-photon ionization (MPI) has the potential to provide sensitive and material selective detection of organic compounds. Coupling this technique with chromatographic methods, such as TLC and HPLC, may result in powerful analytical tools. -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 -2 0 2 4 6 8 10 12 slope = 10.23747 benzo(e)pyrene perylene slope = 0.65486 MPI signal, mV* s Normalized Absorbance Figure 7 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000 18 20 22 24 26 28 30 32 34 36 distance from start,m m M PI sign al, m V *m klit Pyren e 1-B rom Pyren e Figure 3c 0 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000 10 12 14 16 18 20 22 24 26 28 30 32 34 distance from start, m m M PI signal,m V*m icrosec II I II I Figure 5
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Nd-YAG. 3 rd harmonic 355 nm. Imaging Fluorescence (UV Absorbance) Detection. Power Supply. PAH mixture solution. TLC (HPLC) Analysis. Multiphoton Ionization Fast Conductance Detection. Current Amplifier. XY- stage for TLC plate. - PowerPoint PPT Presentation
Transcript of Application of Laser Multi-Photon Ionization to Trace Detection in Chromatography
Application of Laser Multi-Photon Ionization to Trace Detection in Chromatography
Victoria Fun-Young, Iris Litani-Barzilai, Valery Bulatov, Vladimir V. Gridin, and Israel Schechter
Department of Chemistry, Technion - Israel Institute of Technology, Haifa 32000, Israel
ABSTRACT
Multi-photon ionization (MPI) has the potential to provide sensitive detection of a large variety of organic compounds. Coupling this technique with chromatographic methods, such as TLC and HPLC, may result in powerful analytical tools. Moreover, enhanced performance is expected when applying the resonant multi-photon ionization mode of operation.
We examined the feasibility of utilizing MPI in conjunction with TLC and HPLC. The fast-conductivity method was applied, such that direct results can be obtained under ambient conditions. In particular, we focused on detection of polycyclic aromatic hydrocarbon mixtures, whereby direct MPI scanning of TLC plates were examined.
HPLC detection
The targetThe separation in Thin-Layer Chromatography is commonly observed by fluorescence or optical reflection data. The detection of non-fluorescent and/or colorless compounds is more difficult and uncertain. We suggest an alternative detection scheme, based upon the Laser induced Multiphoton Ionization (MPI) processes.
Imaging Fluorescence (UV Absorbance)
Detection
PAH mixture solutio
n
TLC (HPLC)
Analysis
Multiphoton IonizationFast Conductance
Detection
Figure 1
2
MPI-chromatogram obtained for n-hexane solutions of (a) pyrene, (b) 1-Brom-Pyrene and (c) their 1:1 mixture. Developed on Silica gel 60 precoated TLC plates by Cyclohexane for 20 min.
20000
40000
60000
80000
100000
120000
140000
160000
180000
19 21 23
distance from start, mm
MPI
Sig
nal
, m
V*m
kse
c
20000
40000
60000
80000
100000
120000
140000
160000
25 27 29 31 33
distance from start, mm
MPI Sig
nal
, m
V*m
kse
c
Figure 3a
Figure 3b
Br
Experimental setup
Single-trace TLC analysis
Mixture separation/TLC
The mixture of Benzo(e)pyrene (I), Pyrene (II) and 1-Bromopyrene (III) in n-hexane 1:1:1 was developed by cyclohexane for 25 minutes. The green line presents the fluorescence intensity along the TLC plate, obtained at 254 nm. The yellow line shows the corresponding MPI signals. Observe reliable MPI detection associated with each TLC spot-location.
A simple and low costfast-conductancetechnique (Fig. 2a) provides aphotocurrent read-outdue to the Multi-Photon
Ionization of trace
compounds (Fig. 2b).
-0.0002 0.0000 0.0002 0.0004 0.0006 0.0008 0.0010-4
-3
-2
-1
0
1
Pho
tocu
rren
t / A
rb. U
nits
Time / sec
Benzo[e]pyrene
Figure 2b
Current Amplifier
Storage Oscilloscope
_
Power Supply
+
Nd-YAG
3rd harmonic355 nm
XY- stage for TLC plate
Figure 2a
The same as in Fig. 4 but for a shorter (20 min) TLC development time. The MPI signal of pyrene is strong and readily observed. This demonstrates the situation where a poor fluorescing material can be detected by the MPI facility.
Observe, however, that the MPI based separation of pyrene (II) and 1-Bromopyrene (III), seems incomplete. This is a result of the lower development time, since the “tale” of 1-Bromopyrene contributes to the MPI reading of the pyrene spot.
MPI-FC and HPLC data of benzo(e)pyrene, as a function of elution time. The HPLC results are cross-referenced with the corresponding MPI data obtained from the filter substrates.
Conclusions
In order to apply the MPI detection in HPLC, the effluent was transferred to glass fiber filters and the corresponding MPI-FC readings were recorded.
3.6 3.7 3.8 3.9 4.0
0
5
10
15
20
25
HPLC
Abso
rban
ce /
arb.
units
Time / min
3.6 3.7 3.8 3.9 4.0
0
2
4
6
8
10
12
14
MPI
sign
al, m
V*s
MPI
Figure 6
Note the remarkable correspondence of the time-resolved HPLC read-outs to the MPI-FC photocharges.
The molecular selectivity of the MPI detection (in its resonant mode) is exemplified: benzo(e)pyrene is resonatively ionized at 337 nm, while perylene is not. This results in huge differences in the slopes.
0
20000
40000
60000
80000
100000
120000
140000
160000
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
distance from start, mm
MPI
Sig
nal,
mV
*mks
ec/
fluo
resc
ence
inte
nsit
y, a
rb. u
nits
Figure 4
IIII II
Multi-photon ionization (MPI) has the potential to provide sensitive and material selective detection of organic compounds.
Coupling this technique with chromatographic methods, such as TLC and HPLC, may result in powerful analytical tools.
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
-2
0
2
4
6
8
10
12
slope = 10.23747benzo(e)pyrene
perylene
slope = 0.65486
MP
I si
gna
l, m
V* s
Normalized Absorbance
Figure 7
20000
40000
60000
80000
100000
120000
140000
160000
180000
200000
18 20 22 24 26 28 30 32 34 36
distance from start, mm
MPI
sign
al,
mV
*mkli
t
Pyrene 1-BromPyrene
Figure 3c
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
200000
10 12 14 16 18 20 22 24 26 28 30 32 34
distance from start, mm
MPI
sign
al,
mV
*mic
rose
c
IIIIII
Figure 5
