Application of internal quality control to the analysis of quaternary ammonium compounds in surface and groundwater from Andalusia (Spain) by liquid chromatography with mass spectrometry
Introduction
Herbicides and plant growth regulators are essential components of modern agriculture in developed countries and their use is increasing in the third world countries. In agricultural areas, large quantities of these compounds are used, most of them applied directly to the soil or sprayed over the crop fields. In consequence, they can enter as contaminants into natural waters, soils or food. We have focused this study in a particular group of quaternary ammonium compounds for their interest, the paraquat (PQ) and deiquat (DQ) herbicides, and the chlormequat (CQ) and mepiquat (MQ) plant growth regulators. PQ and DQ are non-selective contact herbicides used for the control of weeds and grasses in fruit orchards and for control of aquatic weeds. CQ is registered in at least 17 countries as a plant growth regulator particularly to promote sturdier growth in wheat, rye and oats and thus reduce the risk of lodging. MQ is a plant growth regulator used on cotton to inhibit sprouting [1].
Quaternary ammonium pesticides are commonly known as quats. These compounds are polar and with a high water solubility. So, it is necessary to keep in mind that some of these compounds can arrive easily until the supplies of water. Their ionic character provides them a great mobility in the environment that it is fundamental to control its possible presence in the next places to aquatic supplies. Due to the form in that these substances affect to the environment, some of them have been included on priority lists and are currently regulated in a number of countries [2]. The European Union has not regulated the levels of these compounds in drinking water and continues applying the values of 0.1 μg l−1 for individual pesticides and 0.5 μg l−1 for total pesticides [3].
The analysis of quats in water is difficult. Due to their properties, an ion-pair can be used to be determined by liquid chromatography (LC) with UV detection [4], [5]. However, in order to increase the sensitivity and selectivity, LC coupled with mass spectrometry (MS) is the preferred technique for the determination of these compounds using thermospray [6], particle beam [7], electrospray (ESI) [8], [9], [10], [11] or atmospheric pressure chemical ionization [10]. Because of the large-scale dilution of contaminants in the aquatic matrices, concentrations of many pesticides are below the detection limits of standard analytical and sampling methods. This makes necessary the use of enrichment methods to comply with the maximum legally permitted levels of quats in water samples. Solid-phase extraction (SPE) is a versatile and successfully applied technique in environmental analyses, which has often been recommended for the isolation and concentration of quaternary ammonium herbicides [12]. Cation-exchange resins [7], [13], [14], and other fases such as silica [10], [15], [16], [17] or graphitic carbon [16], [18] have been used to concentrate quats from waters.
In this work, a SPE method with silica cartridges, in combination with LC–MS, has been developed for the determination of four quaternary ammonium compounds in environmental water samples, both surface and groundwater. The methodology was applied to the analysis of real samples from Andalusia (South of Spain), in order to know the pollution levels with these compounds. The study was mainly applied to waters used in rise or olive-tree fields in which the presence of humid acids, surfactants, inorganic salts, other pesticides or related compounds such as metabolites could diminish the recovery and interfere in the instrumental step [19], [20]. Internal quality control (IQC) criteria were observed in the analysis of samples in order to ensure the reliability of the obtained results.
Section snippets
Chemicals and solvents
Chlormequat chloride (98.9%), mepiquat chloride (98.65%), paraquat dichloride hydrate (99.9%), and deiquat monohydrate were purchased from Riedel de Haen (Seelze, Gremany). All these quaternary ammonium compounds were used for preparing 200 mg l−1 stock standard solutions in water–methanol (1:1) and were prepared in plastic material to prevent adsorption and stored 4 °C in the dark. NaOH (99.5%) and HCl 37% were purchased from Panreac (Barcelona, Spain). Heptafluorobutyric acid (HFBA) was obtained
Results and discussion
Until now, some analytical methods have been published for determining quaternary ammonium herbicides in waters using silica cartridges [10], [21], [22]. Also, different LC–MS methods have been described for their analysis [8], [9], [10], [11]. However, few references have been found to the use of silica cartridges in combination with LC–ESI-MS [10]. The LC–MS method described in this work is faster (analysis time lower than 6 min) and more precise than the previously published [10]. Another
Conclusions
Off-line SPE and LC–ESI-MS using the preconcentration of 250 ml of water has been shown to be a good approach for the analysis of paraquat, diquat, chlormequat and mepiquat in water samples. Silica cartridges have showed the best results for the extraction of the target compounds. Validation parameters have shown a good accuracy, precision and lower limits to monitor quats in environmental waters. IQC were established for analysing samples. The method was applied to the analysis of 40
Acknowledgements
The authors are very grateful to Framework Agreement between the University of Almería and the Consejería de Medio Ambiente de la Junta de Andalucía, and also with the Consejería de Educación y Ciencia (Research program ORTI's, empresas andaluzas 2003) de la Junta de Andalucía.
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2016, Journal of Chromatography B: Analytical Technologies in the Biomedical and Life SciencesCitation Excerpt :Therefore, monitoring plasma and urine concentrations of PQ can help to provide valuable information for diagnosis and prognosis. Several methods have been reported for the determination of PQ in different matrices, including water [11–13], agricultural products [14,15] and biological matrices [3,16,17] with gas chromatography (GC) [18], GC-mass spectrometry (MS) [19], high performance liquid chromatography (HPLC) [20] and HPLC–MS [17]. Capillary electrophoresis (CE) [21], CE-MS [22], enzyme-linked immunosorbent assays (ELISA) [23] have also been reported for the quantification of PQ.
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2016, Forensic Science International
Presented at the 3rd Meeting of the Spanish Association of Chromatography and Related Techniques and the European Workshop: 3rd Waste Water Cluster, Aguadulce (Almeria), 19–21 November 2003.