Pre-concentration of pesticides in water using isophorone diamine multiwalled carbon nanotubes-based solid-phase extraction technique and analysis by gas chromatography–mass spectrometry

The existence of pesticides in water at ultra-trace levels necessitates the use of a suitable pre-concentration method for their detection. The objective of this study was to develop an ultra-synthetic adsorbent to extract chlorpyrifos (CPF) and imazalil (IMA) pesticides in water. X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy confirm that both oxidised and isophorone diamine multiwalled carbon nanotubes (IPD-MWCNTs) were successfully prepared with an intact structure; which was further confirmed by transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). The Brunauer–Emmet–Teller (BET) showed a high surface area of both oxidised and IPD-MWCNTs, which is linked to the formation of additional active sites. TGA further showed that the nanocomposites were highly stable within the pesticides quantification operating temperature. CPF and IMA were recovered using a low dosage of IPD-MWCNTs adsorbent (0.030 g) and eluted by a combined solvent (ethanol and chloroform (50:50, v/v)). The adsorbent was reusable over seven repeated cycles, with an acceptable percentage relative standard deviation (%RSD) ranging from 3 to 8%. The IPD-MWCNTs adsorption sites are highly stable and cannot be easily fouled, as compared to that of oxidised MWCNTs. Lower limits of detection (LOD) and quantification (LOQ) for CPF (0.026 and 0.078 µg.L⁻¹) and IMA (0.033 and 0.100 µg.L⁻¹) were achieved. Better recoveries for both analytes at low and high concentrations (as well as in real water samples) were obtained by IPD-MWCNTs whereas a conventional adsorbent (i.e. polymeric reverse phase) can only achieve better recoveries at high concentrations.