Jurnal Sains Kimia
Vol.8, No.1, 2004: 4-7
4
THE USE OF MIREX AS INTERNAL STANDARD AND DCBP AS
VOLUMETRIC STANDARD FOR DETERMINATION
OF ORGANOCHLORINE PESTICIDE IN SEDIMENT
USING GC-MS IN CI+ MODE
Chairuddin
Jurusan Kimia FMIPA Universitas Sumatera Utara
Jl. Bioteknologi No. 1 Kampus USU Medan 20155
Abstract
In this work, mirex was used as an internal standard for the analysis organochlorine pesticides in sediment using GC-MS. The reproducibility of relative retention time was calculated using the volumetric standard method with decachlorobiphenyl (DCBP) as reference compound. Mirex and DCBP were found to be suitable volumetric and internal standard, respectively. Mirex and DCBP did not interfere in the chromatographic separation of the target compounds.
Keyword : Organochlorine, Pesticides, Mirex
INTRODUCTION
GC-MS has become an extremely useful technique for the detection and identification organochlorine pesticide. Quantitative analysis is based on combination of internal and external standardization methods. The internal standard technique is widely used in chromatography. This method is most important analysis because data of high precision and accuracy are obtained for individual components of even complex mixtures. A carefully measured quantity of an internal standard substance is introduced to each standard and sample, and the ratio of analyte peak area to the internal standard peak area is calculated. Internal standards are required due to the potential losses during the work-up, chromatographic steps and variations in instrument response, thus reducing uncertainties. With the small samples
needed for GC-MS, these uncertainties are often a source of indeterminant error.
This study presents a mirex as internal standard in the analysis of organochlorine pesticides (aldrin, dieldrin and endrin) in sediment. Decachlorobiphenyl (DCBP) was used as a volumetric standard to correct small variation in the instrumental response and injection volume by rationing all peak measurements to that of the known amount of the volumetric standard.
MATERIAL AND METHODS
Standard and Reagents
The use of mirex as internal standard and DCBP as volumetric standard (Chairuddin)
5 8a-octahydro-6, 7-epoxy-1, 4z:5, 8
dimethanona-phthalene), mirex (dodecachloropentacyclodecane), DCBP
(decachlorobiphenyl) were purchased from British, Greyhound, Birkenhead, Merseyside, UK. All substances were of 99% purity and were used as received. Hexane was HPLC-grade. . Acetone and diethyl ether were analar-grade. Anhydrous sodium sulphate was obtained from Fisons. Aluminium oxide 90 with particle size 0.083-0.200 mm (70-230 mesh ASTM) was purchased from Merck.
Stock and Standard Solutions
The stock solution of 100 mgL-1 of each of aldrin, dieldrin, and endrin were prepared by accurately weighing the pure materials and dissolving in hexane. The stock solutions of 100 mgL-1 mirex and DCBP were also prepared in hexane. The stock solution, internal and volumetric standards were stored at 4oC and protected from the light
Recovery Studies
The spike solutions of aldrin, dieldrin, endrin and mirex were prepared in acetone.10 g clean sediment was spiked with 10 mL of 40, 100, and 400 μgL-1 of aldrin, dieldrin, endrin and mirex. Spiked sediments were agitated for three hours before proceeding with the ultrasonic extraction. The spiked sediment was sonicated with 3x30 mL hexane for 30 min. The extract solution was filtered through anhydrous sodium sulphate and evaporated to a volume of about 10 mL. The extract was concentrated by blowing with nitrogen until the volume was reduced to about 1 mL.
The clean up procedure was performed using basic/acidic alumina[1]. The extract solution was transferred onto the alumina column. The analytes were eluted with 5 mL of diethyl ether/hexane (3:7) eluant. Eluate was collected and
dried slowly on a nitrogen. 1 mL of 50 µgL-1DCBP was added as a volumetric standard. The eluate was kept in a sealed vial until injection into GC-MS.
Instrumentation GC-MS analysis was performed on a Hewlett Packard 5980 series II gas chromatography interfaced to a VG-TRIO 1000 quadrupole mass spectrometer. The GC-MS system was controlled by the LAB-BASE data processing system and it was run by an Intel 386 PC 32-bit computer. A fused-silica capillary column DB5-MS (J&W Scientific), 15 m long, 0.32 mm internal diameter and 0.25 μm film thickness, was inserted directly into the ion source using helium (CP grade, purity 99,999%) as a carrier gas.
The GC was operated in the splitless mode with the injector temperature at 270oC. 1 μL sample was injected manually. The septum purge on-time was 1.0 min. The gas chromatography oven temperature was follows: Initial ramp 100oC held for 1 min, 20oCmin-1 to 300oC held for 3 min. The total time per analysis for each samples was 14 min.
The instrument settings were as follows: Ionizing voltage 70 eV, ionizing current 200 μA, ion source temperature 200oC, interface temperature 250oC, scan range 50-650 u and scan time 0.90 s with interscan 0.10 s for full scan and 0.02 u with 0.08 s dwell time for SIR.
In the analysis of spike samples, the selected ion recording (SIR) mode of operation of the mass spectrum under CI- was employed.
RESULTS AND DISCUSSION
Jurnal Sains Kimia
Vol.8, No.1, 2004: 4-7
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chemical ionization mode is shown in Figure 1.
Hexane was used as a solvent using ultrasonic extraction to investigate the recovery efficiency of the aldrin ,dieldrin, endrin, and mirex from spiked clean sediment samples.
Figure 1. Total ion chromatogram (TIC) of aldrin (5,96), dieldrin (6,99), endrin (7,18), mirex (8,68) and DCBP (9,76)
Mirex did not interfere in the chromatographic separation of aldrin, dieldrin, and endrin. This compound was chosen as an internal standard because it was not present in the samples to be analysed and had a similar analytical behaviour to aldrin, dieldrin , and endrin (cyclodiene group). The use of mirex as internal standard in sediment, moss and fish for analysis of synthetic phyretroids with the three solvent systems hexane, dichloromethane and acetone/hexane has been reported[2]. Picer and Picer[3] reported that mirex is more convenient as an internal standard because the appearance of interfering peaks at its retention time in a GC chromatogram is of a lower probability than the appearance of such peaks at the aldrin retention time. The internal standard, mirex was used in this study as a quality control and quality assurance monitor the whole analytical procedure.
The percent recovery results of aldrin, dieldrin, endrin, and mirex at the three spiked level (40, 100, and 400 μgkg-1) using ultrasonic extraction are shown in Table l. It shows that the average percentage recovery of aldrin, dieldrin, endrin and mirex from the spiked sediment in the concentration range 40-400 μgkg-1 using hexane as a solvent system in ultrasonic extraction was higher than 60%. The data indicates quite satisfactory recoveries of target analytes for the extraction of aldrin, dieldrin, and endrin from contaminated sediment.
Table 1. Recovery of aldrin, dieldrin, endrin, and mirex from spiked sediment at 40, 100 and 400 μgkg-1 with hexane as a solvent system using ultrasonic extraction Standard Deviation
n : 4
The use of mirex as internal standard and DCBP as volumetric standard (Chairuddin)
7 standard. Thereby errors in the analytical
measurement are often reduced, since any loss of sample is compensated by loss of an equivalent amount of volumetric standard. Volumetric standard can thus serve two roles, primarily to compensate for actual sample volume injected and secondly as a check on the retention times. Its retention will be sensitive to any changes due to leaking septa or temperature variation of the column. The relative retention times (RRT) of aldrin, dieldrin, endrin and mirex are shown in Table 2.
Table 2. Relative retention times (RRT) of aldrin, dieldrin, endrin, and mirex
Compound RRT SD
Aldrin Dieldrin
Endrin Mirex DCBP
0.595 0.0005 0.705 0.0033 0.725 0.0043 0.883 0.0005 1.000; tR = 9.00 min
n =14
The reproducibility of relative retention times was extremely good, with standard deviations typically less than 0.0050%. This report was calculated from a calibration curve for aldrin, dieldrin, endrin and mirex by using the volumetric standard method with DCBP as reference compound.
CONCLUSION
The recovery data for mirex illustrates its suitability as an internal standard for organochlorine pesticide monitoring in sediment and mirex can monitor the losses during the different stages of extraction.
DCBP was a suitable volumetric standard for the analysis of aldrin, dieldrin, endrin and mirex because its reproducibility of relative retention times is extremely good and it has a limited number of mass spectral fragments , above the MS background with a high electron affinity.
REFERENCES
Best, G.E. and Dawson, J.P. 1993., “Environmental analysis using gas chromatography, in Gas Chromatography; a practical approach”, edited by P.J.Baugh, The practical approach series, Oxford University Press, Oxford, 283-329.
Yasin, M, P.J.Baugh, P.Hancock, G.A.Bonwick, D.H.Davies, and R.Armitage, Rapid. Comm. 1995., “Mass Spectro”., 9 , 1411-1417
Picer,M and Picer, N. 1983., “Ocean Scie”.Eng., 8 (1), 63-69
Wells, D.E and Cowan, A.A., J. 1983., “Chromatogr”. 279, 209-218
