Wan Mohd Afiq Wan Mohd Khalik

Determination of pesticide residues in leafy vegetables at parts per billion levels by a chemometric study using GC-ECD in Cameron Highlands, Malaysia

A simple and sensitive analytical method has been developed employing gas chromatography coupled with electron capture detector (GC-ECD), and validated for screening and quantification of 15 pesticide residues at trace levels in cabbage, broccoli, cauliflower, lettuce, celery, spinach, and mustard. The method consists of two steps, first, to determine the significance of each factor by Pareto chart followed by optimization of these significant factors using central composite design (CCD). Minitab statistical software was used for these multivariate experiments for the generation of 24-1 design and CCD matrices. The method evaluation was done by external standard calibration with linearity range between 0.5 and 3mg/kg, with correlation coefficient 0.99, limit of detection (LOD) ranges between 0.02 and 4.5ng/g, and limit of quantification (LOQ) ranges between 0.2 and 45ng/g. The average recovery was between 60% and 128%, with RSD 0.2-19.8%. The method was applied on real vegetable samples from Cameron Highlands.

Penilaian pengekstrakan erapan bar untuk pengekstrakan herbisid triazin menggunakan pendekatan reka bentuk komposit berpusat

A (PDMS)-coated stir bar was prepared for a glass jacket-free stir bar sorptive extraction (SBSE) configuration by adhesion technique for the extraction of triazine herbicides prior to quantification using a gas chromatography-flame ionization detector (GC-FID). A central composite design (CCD) was used in the optimization of extraction and desorption conditions. At optimum conditions, values of factors were set as pH 8.5, with no addition of NaCl, for 25 minutes of extraction time, and 24 minutes of desorption time. Under optimal experimental conditions, the proposed method has linear ranges at 0.1 – 100 µgL-1 with correlation of determination (R2), ranging from 0.9991 – 0.9995, respectively. The limit of detection (LODs) and limit of quantification (LOQs) of three triazines were found to be ranging from 0.015 – 0.023 µgL-1 and 0.047 – 0.060 µgL-1, respectively.

Development of extraction procedure for determination of mercury species using SPME-assisted dispersive derivative agent

The extraction procedure for determination of low level mercury using solid phase microextraction was successfully carried out. Design of experimental works using factorial design and central composite design were applied to screen and predict the optimum condition for extraction step. In this study, variables namely concentration level (5 % m/v) and volume of derivatization solution (150 µL) has depicted as main effect for controlling the suitability of derivative reagent condition. Maximum of signal response (account as total peak areas for mercury species) was obtained when extraction procedure was set up at pH of water sample (5.8), extraction time (14 min), extraction temperature (43 °C) and stirring rate (450 rpm). Reducing time required to reach equilibrium is new improvement achieved in this study. Detection limit for each species (MeHg 26.17 ngL−1; EtHg 48.84 ngL−1 and IHg 14.11 ngL−1) was calculated lower than our previous work. Recovery, repeatability and reproducibility trial were recorded var...

Characterization of spatial and temporal variability in hydrochemistry of Johor Straits, Malaysia.

Characterization of hydrochemistry changes in Johor Straits within 5 years of monitoring works was successfully carried out. Water quality data sets (27 stations and 19 parameters) collected in this area were interpreted subject to multivariate statistical analysis. Cluster analysis grouped all the stations into four clusters ((Dlink/Dmax) × 100<90) and two clusters ((Dlink/Dmax) × 100<80) for site and period similarities. Principal component analysis rendered six significant components (eigenvalue>1) that explained 82.6% of the total variance of the data set. Classification matrix of discriminant analysis assigned 88.9-92.6% and 83.3-100% correctness in spatial and temporal variability, respectively. Times series analysis then confirmed that only four parameters were not significant over time change. Therefore, it is imperative that the environmental impact of reclamation and dredging works, municipal or industrial discharge, marine aquaculture and shipping activities in this area be effectively controlled and managed.