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INTRODUCTION
Research associated with the development of new crop protection
chemicals centers around the design of products that provide highly
effective and specific action towards the target organism with
reduced application rates. It is estimated that 25-30% of the
pesticides on the market today have optical isomers. The desired
activities often result from a single enantiomer in the optical isomer
mixtures. It is therefore important to assess the enantiomeric purity
of the chiral active ingredients in the formulation. In addition, the
detection, characterisation and quantitation of the other components
in the formulation are necessary to support product registration.1
There has been an increasing adoption of supercritical fluid
chromatography (SFC) on chiral stationary phases for chiral
separation. The properties of a supercritical fluid, its high diffusivity
and low viscosity in particular, enable high efficiency chiral
separations with shorter run times. UltraPerformance Convergence
Chromatography (UPC2) applies the performance advantages of
UPLC® to SFC, combining the use of supercritical CO2 with sub-2-μm
particle columns. UPC2 is an orthogonal analytical technique to
reversed-phase LC and can be used to solve complex separations
challenges.
In this study the achiral screen of a formulated pesticide product
using UPC2 showed that the minor components detected using UV
and mass detection had similar structural characteristics to the
active ingredient (AI), propiconazole, a triazole fungicide with two
chiral centers (Figure 2). The minor components had the same m/z
and shared the same isotopic pattern as the AI. Subsequent chiral
resolution of the propiconazole in the formulation in combination
with simultaneous UV and mass detection provided valuable spectral
information which allowed the minor components to be characterised
as probable stereoisomers.1
Chiral and Achiral Profiling of a Pesticide Formulation
using UltraPerformance Convergence Chromatography
(UPC2) with PDA and Mass Detection
Marian Twohig,1 Jane Cooper,2 Hélène Boiteux,3 John McCauley4 1Waters Corporation, Milford, MA, USA; 2Waters Corporation, Wilmslow, UK; 3Waters Corporation, 5 rue Jacques Monod, 78280 Guyancourt, France. 4Waters Corporation, New Castle, DE, USA.
PDA
QDa
Figure 1. Waters® ACQUITY QDa Detector is a novel mass
detector that can be integrated into existing liquid chromatography configurations in order to increase sensitivity
and complement the results obtained using UV detectors.
Table 1. Summary of the analysis conditions.
RESULTS AND DISCUSSION Achiral Separation
ACQUITY UPC2 chromatograms (Figure 2) of the
propiconazole standard (lower trace) and the formulation
sample (top trace) obtained using an ACQUITY UPC2 BEH
column.
The retention times of peaks 1 and 2 (propiconazole
diastereomers) in the formulation sample matched those of
the propiconazole standard.
Two minor peaks (peaks 3 and 4) were observed in the
formulation sample with retention times (tR) of 2.22 min and
tR 2.26 min, respectively.
The UV spectra of peaks 3 and 4 resemble those for peaks 1
and 2 (Figure 2), indicating their structural similarity. In
addition, the four peaks resulted in identical mass spectra
with base peaks at m/z 342 and an isotopic pattern
characteristic of dichlorinated compounds. The m/z matched
the protonated propiconazole.
Figure 2. ACQUITY UPC2 UV achiral separation of the propiconazole
present in the formulation sample and propiconazole standard at 220 nm using the ACQUITY UPC2 BEH Column. The UV and MS spectra for peaks 1-
4 are also shown.
Chiral Separation
The ACQUITY UPC2 System has multi-column switching capabilities and a choice of up to four co-solvents which
allows both achiral and chiral method development and sample analysis to be performed on the same system.
Using gradient separation on an ACQUITY UPC2 Trefoil AMY1
chiral column (Figure 3). The two diastereomer peaks of propiconazole observed in Figure 2 were baseline resolved
into four individual peaks (1-4). Interestingly, the two minor isomer peaks in Figure 2 were also resolved into four peaks
(5-8) in a comparable manner, indicating a similar chirality for propiconazole and the minor components.
References
1. Twohig, M. O’Leary, M. McCauley, J.P. Chen, R. Chiral and Achiral Profiling of
a Pesticide Formulation Using the ACQUITY UPC2 System and the ACQUITY
QDa Detector. Waters application library. APNT134790013.
2. Glaser, R. Adin, I. Ovadia, D. Mendler, E. Drouin, M. (1995) Solid-state
structure determination and solution-state NMR characterization of the
(2R,4R)/2S,4S)- and (2R,4S)/(2S,4R)-diastereomers of the agricultural
fungicide propiconazole, th(2R,4S)/(2S,4R)-symmetrical triazole
constituational isomer, and a ditriazole analogue. Structural Chemistry, Vol
6, No 3. 145-156.
3. McCauley, J.P. Twohig, M. Chen, Rui. Isolating Trace Impurities for
Structural Elucidation in a Commercial Fungicide Formulation Using
Preparative SFC. Chirality 2014 Prague, Czech Republic. July 27th to 30th
2014. Waters application library PSTR134807862.
CONCLUSION The addition of mass detection as a complementary
analytical detection technique enhances confidence
in compound detection and identification.
The ACQUITY UPC2 System has column switching
capabilities so that both chiral and achiral columns
can be used with a choice of four co-solvents that are
compatible with MS analysis. The chiral and achiral
method development and analysis can be performed
on the same system.
The ACQUITY UPC2 System allows high efficiency
separations that can increase sample throughput
compared to traditional normal-phase separations.
The diasteromeric resolution of propiconazole using
UPC2 took place in less than 3 minutes, which is at
least 10 times faster than normal phase methods
reviewed in the literature.1
Matrix components visible in the UV chromatogram and the MS total ion chromatogram (TIC) of the formulation
sample are clearly differentiated from the isomeric peaks of interest using an extracted ion chromatogram (XIC)
(inset Figure 3).
The detection sensitivity and selectivity of the method are improved when using mass detection in combination with
UV detection which is used in order to measure the enantiomeric purity of the chiral pesticide in the
formulation.
Based on the observations, it is postulated that the minor component is a regioisomer of propiconazole. A
regioisomer of propiconazole originating from one of the
nitrogens on the triazole ring was characterised by Glaser et al.2
Further experiments to characterise and isolate this
compound for positive identification were carried out. Methods were developed to scale separations to SFC
preparative chromatography, each minor stereoisomer was isolated followed by characterisation using 1H, 13C,
2D and NOE NMR spectroscopy. These experiments revealed that the minor isomer peaks differed from
propiconazole itself by the the triazole nitrogen attachment point to the methylene group that is bridging
to the dioxolane ring. The assigned structures for the all of the isolated components were in agreement with the
information in the prior literature by Glaser et al.2,3
Figure 3. ACQUITY UPC2 UV chromatogram at 220 nm showing the chiral resolution of the propiconazole stereoisomers and unknown
chiral components in the formulation sample using the ACQUITY UPC2 Trefoil AMY1 column. The XIC of m/z 342 and the UV and MS spectra for each peak are also shown.
Reproducibility
Empower 3 can be used to assess the peak attributes with its
system suitability function. Chromatographic parameters can
be determined and statistical measurements can be made on
them. In this example the RSDs for 10 determinations of the
retention time, area, area % height and USP resolution were
< 0.61% for all of the propiconazole stereoisomers (Table 2).
Table 2. RSD for ten replicate injections of the propiconazole stereoisomers in the formulation sample.
%RSD (n=10)
PropiconazoleStereoisomers
tR Area Area % Height USP Resolution
Peak 1 0.37 0.44 0.09 0.61
Peak 2 0.33 0.39 0.05 0.52 0.43
Peak 3 0.27 0.37 0.05 0.57 0.29
Peak 4 0.22 0.37 0.04 0.61 0.21
342
344
Intensity
0.0
5.0x106
1.0x107
342
344
Intensity
0.0
5.0x106
1.0x107
342
344
Intensity
0.0
5.0x106
1.0x107
1.5x107
342
344
Intensity
0.0
5.0x106
1.0x107
1.5x107
m/z
320.00 325.00 330.00 335.00 340.00 345.00 350.00 355.00 360.00
256.9 269.9 307.9 341.0
AU
0.000
0.001
0.002
271.1 337.6
AU
0.001
0.002
219.2
269.9 307.9 327.0 338.8
AU
0.000
0.001
0.002
0.003
266.4 319.8 352.7
AU
0.000
0.001
0.002
0.003
0.004
nm
220.00 240.00 260.00 280.00 300.00 320.00 340.00 360.00
342
344
Intensity
0.0
5.0x106
1.0x107
1.5x107
342
344
Intensity
0.0
5.0x106
1.0x107
342
344
Intensity
0
2x106
4x106
6x106
342
344
Intensity
0
2x106
4x106
m/z
320.00 325.00 330.00 335.00 340.00 345.00 350.00 355.00 360.00
268.8
AU
0.00
0.10
0.20
268.8
AU
0.00
0.10
0.20
268.8
AU
0.00
0.10
0.20
0.30
268.8
AU
0.00
0.10
0.20
0.30
nm
220.00 240.00 260.00 280.00 300.00 320.00 340.00 360.00
AU
0.00
0.05
0.10
0.15
0.20
0.25
Intensity
0.0
2.0x108
4.0x108
6.0x108
8.0x108
1.0x109
1.2x109
1.4x109
1.6x109
Minutes
0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50
PDA 220 nm
XIC m/z 342
12
3 4
58
6 7
1
2
3
4
1
2
3
4
5
6
7
5
6
7
8 8
12
3 4
5 86 7
AU
-0.010
0.000
0.010
0.020
0.030
0.040
Intensity
-5.0x107
0.0
5.0x107
1.0x108
1.5x108
2.0x108
2.5x108
Minutes
4.00 5.00
AU
-0.010
0.000
0.010
0.020
0.030
0.040
Intensity
-5.0x107
0.0
5.0x107
1.0x108
1.5x108
2.0x108
2.5x108
Minutes
4.00 5.00
AU
-0.010
0.000
0.010
0.020
0.030
0.040
Intensity
-5.0x107
0.0
5.0x107
1.0x108
1.5x108
2.0x108
2.5x108
Minutes
4.00 5.00
PDA 220 nm
XIC m/z 342
5 86 7
AU
-0.010
0.000
0.010
0.020
0.030
0.040
Intensity
-5.0x107
0.0
5.0x107
1.0x108
1.5x108
2.0x108
2.5x108
Minutes
4.00 5.00
AU
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Intensity
0.0
2.0x108
4.0x108
6.0x108
8.0x108
1.0x109
1.2x109
1.4x109
Minutes
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 3.40 3.60 3.80 4.00 4.20 4.40 4.60 4.80 5.00 5.20 5.40 5.60 5.80 6.00 6.20
1 2
3 4
1 2 3 4
5 6 7 8
AU
-0.010
-0.008
-0.006
-0.004
-0.002
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
Intensity
-6.0x107
-4.0x107
-2.0x107
0.0
2.0x107
4.0x107
6.0x107
8.0x107
1.0x108
1.2x108
1.4x108
1.6x108
1.8x108
2.0x108
2.2x108
2.4x108
Minutes
4.60 4.80 5.00 5.20 5.40 5.60 5.80 6.00
AU
-0.010
-0.008
-0.006
-0.004
-0.002
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
Intensity
-6.0x107
-4.0x107
-2.0x107
0.0
2.0x107
4.0x107
6.0x107
8.0x107
1.0x108
1.2x108
1.4x108
1.6x108
1.8x108
2.0x108
2.2x108
2.4x108
Minutes
4.60 4.80 5.00 5.20 5.40 5.60 5.80 6.00
AU
-0.010
-0.008
-0.006
-0.004
-0.002
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
Intensity
-6.0x107
-4.0x107
-2.0x107
0.0
2.0x107
4.0x107
6.0x107
8.0x107
1.0x108
1.2x108
1.4x108
1.6x108
1.8x108
2.0x108
2.2x108
2.4x108
Minutes
4.60 4.80 5.00 5.20 5.40 5.60 5.80 6.00
AU
-0.010
-0.008
-0.006
-0.004
-0.002
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
Intensity
-6.0x107
-4.0x107
-2.0x107
0.0
2.0x107
4.0x107
6.0x107
8.0x107
1.0x108
1.2x108
1.4x108
1.6x108
1.8x108
2.0x108
2.2x108
2.4x108
Minutes
4.60 4.80 5.00 5.20 5.40 5.60 5.80 6.00
PDA 220 nm
5 6 7 8
XIC m/z 342
5 6 7 8
PDA 220 nm
QDa XIC m/z 342
Rs1,2 = 2.42Rs2,3 = 2.28Rs3,4 = 2.40
METHODS Achiral Gradient Conditions:
0 min 3% B, 4 min 30% B, 6 min 30% B, return to initial
conditions.
Chiral Gradient Conditions:
0 min 7% B, 3 min 11% B, 6 min 17% B, 7 min 40% B, return to
initial conditions.
Mass Detector Conditions
MS system: ACQUITY QDa Detector
Ionization mode: ESI+ ; Capillary voltage: 1.0 kV
Desolvation temp.: 600 °C ; Source temp.: 150 °C
Cone voltage: 10 V; Sampling rate: 5 Hz
MS scan range: 100 to 600 m/z
Empower 3 FR2 Software was used for data acquisition and
chromatographic data processing.
342
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Intensity
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1.0x107
1.5x107
342
344
Intensity
0.0
5.0x106
1.0x107
342
344
Intensity
0
2x106
4x106
6x106
342
344
Intensity
0
2x106
4x106
m/z
320.00 325.00 330.00 335.00 340.00 345.00 350.00 355.00 360.00
268.8
AU
0.00
0.20
0.40
0.60
0.80
268.8
AU
0.00
0.20
0.40
0.60
0.80
313.9 343.3
AU
0.000
0.010
0.020
268.8 327.0 339.9
AU
0.000
0.005
0.010
0.015
nm
220.00 240.00 260.00 280.00 300.00 320.00 340.00 360.00
AU
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
AU
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Minutes
0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00
AU
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
AU
-0.006
-0.004
-0.002
0.000
0.002
0.004
0.006
0.008
Minutes
2.20 2.40
12
12
Formulation
sample
Propiconazole standard
3
4
1
2
3
4
1
2
3
4
34
(2R,4R)-propiconazole
(2R,4S)-propiconazole
(2S,4S)-propiconazole
(2S,4R)-propiconazole
UV SpectraPDA 220 nm MS Spectra
Achiral Chiral
Separation mode Gradient Gradient
Column ACQUITY UPC2 BEH, 3.0 x 100 mm, 1.7-μm
ACQUITY UPC2 Trefoil AMY1 3.0 x 150 mm, 2.5-µm
Co-solvent (B) Methanol 50:502-propanol/ethanol
ABPR 1990 psi/137 bar 3000 psi/207 bar
Flow rate 1.5 mL/min 1.5 mL/min
UV detection 220 nm 220 nm
Column temp. 35 °C 20 °C
Injection volume 0.5 µL 0.5 µL
Make-up solvent 98:2 methanol:water with 0.1% ammonium hydroxide at 0.3 mL/min