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Chlormequat & Mepiquat
Plant Growth Regulators
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printable Application Sheet
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Notes: Chlormequat and mepiquat are quaternary ammonium compounds (quats) which are used as plant growth control regulators to
reduce unwanted shoot growth without lowering plant productivity. CQ and MQ are used on fruits, vegetables and on food crops,
which are used for making cereals. The compounds are considered by World Health Organization (WHO) as hazardous and their
maximum residue levels (MRLs) have been established and regulated. For example in cereals, MRLs range from 0.5 to 5 mg per kg
for both compounds.
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Method Conditions
| Column |
Cogent Diamond Hydride™, 4µm, 100A |
| Catalog No. |
70000-15P-2 |
| Dimensions |
2.1 x 150 mm |
| Solvents |
A: DI water + 20 mM ammonium ascetate, pH adjusted to pH 3.3 with
formic acid
B: Acetonitrile |
| Mobile Phase |
70%A |
| Post time |
5 min |
| Flow rate |
0.5 mL/min. |
| Sample Peaks |
1. Chlormequat (CQ) 122.0737 m/z (M)+
2. Mepiquat (MQ) 114.1277 m/z (M)+
Sample stock solutions were purchased from Sigma. Samples for injection were
diluted 1:1000 in the mobile phase.
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| Detection |
ESI – pos. - Agilent 6210 MSD TOF mass spectrometer.
CQ and MQ are already charged in solution and under ESI conditions the mass spectra show abundant molecular ion (M)+. |
Discussion
Analysis of CQ and MQ can be challenging since they are extremely hydrophilic and are only weakly retained in reversed-phase HPLC
which makes their separation impossible. In addition these compounds are retained too strongly in normal phase (non polar solvents)
chromatography Due to this situation the preferred method of analysis for these compounds was ion-pair chromatography using high ionic
strength (> 150 mM) ion-pair reagents. Buffers used are at very high concentration which makes coupling with MS very difficult if
not impossible (source contamination). This note shows a new, sensitive and selective LC-MS method with low ionic strength mobile
phase for the analysis of CQ and MQ residues. The method can be used in analysis of many samples including food. The selectivity and
sensitivity of the method can be increased by using LC-MS-MS instrument and adequate product ions (CQ 122 m/z to 58 m/z and 63 m/z, MQ
114m/z to 98 m/z and 58 m/z). This method has high repeatability (precision) and reliability of the results.
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