(EXPERIMENT 7) ANALYSIS OF CHLORPYRIFOS IN WATER BY SOLID-PHASE EXTRACTION (SPE) AND GAS CHROMATOGRAPHY-ELECTRON CAPTURE DETECTOR (GC-ECD) NAME:
MOHAMAD NOR AMIRUL AZHAR BIN KAMIS
STUDENT ID:
2014647344
PARTNERS’ NAMES: 1.
MOHAMAD HAMIZAN BIN MOHD ISA
2.
MOHAMAD SHAFIQ BIN PARMAN
3.
MOHAMAD AZMIZAM BIN MOHAMAD NOOR
DATE OF EXPERIMENT:
17/10/2014
DATE OF SUBMISSION:
8/12/2014
INTRODUCTION:
Figure 1: chlorpyrifos Chlorpyrifos is a crystalline organophosphate insecticide that acts on the nervous system of insects by inhibiting acetylcholinesterase. Chlorpyrifos is moderately toxic to humans and the exposure will cause neurological effects such as persistent developmental disorders autoimmune disorders and children mental development retard due to the exposure during pregnancy. In agriculture, chlorpyrifos remains as one of the most widely used as the pesticide. Solid-phase extraction (SPE) is an extraction method that uses solid and liquid phase to isolate analyte from solution. It is a rapid and selective sample preparation. The purpose of using the SPE is to purify, trace enrichment, solvent exchange and derivatization. The advantages of the SPE are high recovery of analyte, concentration of analyte, ease of automation and reduction of organic solvent consumption. The general procedure of SPE is the loading of solution through SPE phase, wash away undesired components, and lastly wash off the desired analytes with other solvent into the collection tube. Steps of SPE are from column solvation and equilibration, sample loading, interference elution and lastly, the analyte elution. The objectives of this experiment are to calculate the amount of chlorpyrifos and each waste water sample and also the percentage of recovery.
EXPERIMENTAL: a. Solid-phase extraction procedure: 1. 10mL of methanol was let to be passed the C18 SPE cartridge to activate the column. 2. 6mL of deionized water was let to be passed the cartridge without applying the vacuum to remove the excess solvent prior to adding the sample. 3. The filtered water sample (50mL) was let to be passed through the preconditioned column using a vacuum manifold at about 48-55 drops/min. The column was not let dry during the sample enrichment step.
4. The column was dried by using the vacuum for 15 minutes. 5. The interference was removed by eluting the column with 10mL of deionized water and the column again was dry by using vacuum for 30 minutes. 6. The pesticide was eluted by using 5mL of hexane and then was concentrated into about 1mL by gently blowing with nitrogen. b. Instrument set-up: Injector temperature: 280°C Detector temperature: 300°C Carrier gas flow rate: 20.0mL/min (nitrogen) Column temperature: initial temperature 165°C for 3 minutes, increase to 260°C at 3°C/min with a final time of 2 minutes. c. Quantitative analysis of chlorpyrifos: 1. 1μL of sample was injected onto the column and to get the reproducible peak, the injection was repeated for each sample. 2. 1μL of standard chlorpyrifos (30ppm) was injected and the injection was repeated to get reproducible peak area. 3. By using the data from the standard solution of chlorpyrifos, the concentration of chlorpyrifos in the samples were calculated.
RESULT AND DISCUSSION: A. Comparison in retention time of standard and samples: Retention Sample Retention time of sample time of (min) standard (ppm)
6.901
Average retention time of sample (min)
1
Trial 1 6.919
Trial 2 6.919
6.919
2 3
6.917 6.920
6.917 6.920
6.917 6.920
B. Calculation of response factor for standard compound: Response Factor (RF) = = = 4.975 × 10-5ppm/Hz*s
C. Amount of chlorpyrifos in samples: Amount of chlorpyrifos in sample = RF standard × peak area sample Sample
1 2 3
Area (Hz*s)
Trial 1 270559 247838 302817
Trial 2 272510 245646 306761
Average area (Hz*s)
Amount of chlorpyrifos (ppm)
270534.5 246742 304789
13.46 12.28 15.16
Average amount of chlorphyrifos in sample = = 13.63ppm D. Percentage of recovery of samples: Percentage recovery = Amount of chlorpyrifos in standard = 30ppm sample Amount of chlorpyrifos in sample (ppm) 1 13.46 2 12.28 3 15.16
× 100% Percentage recovery (%) 44.87 40.93 50.53
Average percentage recovery of sample = = 45.44% In this analysis, GC with Electron Capture detector is used because the analyte to be analysed is halogenated compound. ECD only can detect analytes which contain electronegative functional groups that can capture electrons such as halogens, peroxides, quinones and nitro groups. The disadvantage of ECD is it involve radioactive component. The amount of chlorpyrifos in samples is calculated by using response factor calculation that base on the standard compound. The amount of chlorpyrifos in each sample does not show big different, it show that same procedure was carried out to each sample. The average amount of chlorpyrifos in the samples is 13.63ppm, that is about half from the amount of chlorpyrifos in the standard. The percentage recovery calculated is 45.44% in average. In order to get higher amount of chlorpyrifos or the percentage recovery, the SPE must be carried out carefully so it will extract more chlorpyrifos efficiently.
CONCLUSION: The average amount of chlorpyrifos in sample is 13.63ppm and the percentage recovery is 45.44%.
REFERENCES: 1. Nor’ashikin S., Ruziyati T., Mardiana S. (2012), Analytical Separation Methods Laboratory Guide (2nd edition), 3/10/2014. 2. Clorpyrifos, 30/10/2014, http://en.wikipedia.org/wiki/Chlorpyrifos. 3. Mardiana Saaid, 30/10/2014, Electron-Capture Detector (ECD) lecture notes.
