Analysis of polyaromatic hydrocarbons in water by headspace solid phase micro-extraction coupled with capillary gas chromatography Brannigan du Preez, 1838!18 "#$ 31% &tellenbosch 'ni(ersity
)ntroduction
Headspace solid phase micro-extraction is an efficient procedure in preparing samples in laboratories or on site operations, where the analyte is required to be investigated. This process involves the dispersion the extracted phase onto a solid support which which is exposed to the sample sample for a certain period period of time. Equilibrium is reached between the solid and the extracting extracting phase, whereas whereas in pre-equilibrium extraction the amount of analyte analyte extracted from the sample can be related to time. Quantification of the extracted analyte can be performed based on the time it taes for the analyte to accumulate onto the solid fused silica coating. The above-mentioned procedure can be coupled to capillary gas chromatography, chromatography, whereby a liquid sample is in!ected into an oven, through which it vapourised to passed through a column "moving as the mobile phase by means of a carrier gas#, through which the individual compounds within the sample can be separated according to their respective affinities to the particular stationary phase used. $ chromatographic plot is constructed by the detector, usually performed by a computer, in order to indicate the retention times of each compound. The higher the retention time on the chromatogram, chromatogram, the lower the affinity the compound has for the stationary phase used. Thus, coupling of these techniques enable the anal yses of microsamples of low concentrations, through the micro-extraction of analytes from a gaseous or liquid phase using H%-%&'E( consequently, as previously mentioned, )*-chromatography )*-chromatography allows the separation of mixtures according to their affinities to a particular stationary phase, which in this experiment, are poly-aromatic hydrocarbons within water. +t is useful to be aware of the potential environmental and carcinogenic effects effects these compounds possess. possess. This experiment will enable the presence of such substances, within water, to be determined. These compounds include naphthalene, fluorine and phenanthrene using .-dimethylnaphthalene as an internal standard. H%-%&'E is a reasonably good method by which micro-extraction is performed, as it uses less solvent and it can be used to detect compounds with concentrations as small as μg/. The ob!ectives in this experiment include the extraction of analytes from calibration samples "and unnown samples using H%-%&'E# and the subsequent separation and identification of these samples using )*-analysis. $ calibration curve is drawn using the pea area of the compounds at their respective concentrations, upon which the unnown poly-aromatic hydrocarbons are quantified within the sample.
&le preparation &P$*+"
The sample preparation for %&'E is separated into two stages upon which the first, sorption, involved piercing the sample septum with the in!ector, upon which the fiber extract containing the anal yte was exposed to the headspace "by which vaporisation onto the coating could occur# upon which the fiber was retracted. The second procedure, desorption, desorption, involved the piercing of the *) septum, through the *) *) inlet, by which the fiber was was exposed to release the analyte, into the vapori0ing inlet of the -------- after which the fiber was retracted.
Procedure
$ water sample containing an unnown amount of poly-aromatic hydrocarbons were assigned to be identified, whereas an internal standard of .-dimethylnaphthalene was used. Target analytes were extracted according to %&'E within the calibration and the unnown sample, followed by capillary *)-1+2 analysis. $ calibration curve was obtained for the standards, which were used to quantify the sample.
#&-&P$*. %&'E was performed using an %&'E device, which was equipped with a 334m &2'% fiber, which was conditioned for hours at 5637) within the splitless in!ector.
The extractions were performed within a 53 ml headspace vial which was ept at room temperature. The sample was extracted for 83 minutes, whereby the sample was stirred at 333 rpm, using a magnetic stirrer and a Teflon-coated stirrer bar. ""-/)0. *)-1+2 was performed using an $gilent 69:3 *), containing a splitsplitless in!ector as well as a detector. 1or the separation process, a 83 m capillary column "with a film thicness and internal diameter of 3.56mm and 3.563 mm, respectively. Temperature programming proceeded using ;37) for one minute, increasing it to 5637) "at 67) per minute# for five minutes. The in!ector time was set to 5937) at a t wo-minute splitless time. The carrier gas, whose pressure and flow rate were 33 &a and mlminute respectively, used was helium. The 1+2 temperature was also 5937), with gas pressures of 33 &a of hydrogen and 833 &a of air containing flow rates of 86 and 863 mlminute, respectively.
esults
Concentration of Standards (ppb)
Peak 1
Peak 2
Peak 3
Peak 4
3
;6:,6
<;;85,5
56<5,6
56,6
83
;:<8,
968,9
5;;5,:
53:;,:
63
8889,;
;5,
:5,9
5886,6
<6
;:65,8
9;9;<,<
<:<;,:
633:,
63
39:;9,
68:,3
8;5<,3
9;;:,
=nnown sample
98,;
;6<3:,
89<9,:
69636,9
=nnown sample 5
3<33,<
8;66,:
5:88,9
3;33,8
=nnown sample 8
959,<
;99;,9
899:6,3
;:;8,5
able 1 represents the various pea areas of the compounds at different concentrations "in ppb#. >ote that pea 5 was used as an internal standard.
)orrected &ea $rea
"onc2 of &tandards ppb4
Pea5 1
Pea5 3
Pea5 %
3
3,38<8
3,3<5
3,356
83
3,8
3,<:8
3,39
63
3,58
3,5;38
3,:
<6
3,8<;
3,5;;
3,53:
63
3,<3;3
3,998:
3,65:
'n5nown sample 1
3,5<:5
3,693
3,9:3
'n5nown sample 6
3,56
3,6<
3,:833
'n5nown sample 3
3,5;6<
3,6;65
3,:33
Table 5 represents the corrected pea areas of the compounds at their various concentrations
/igure 6 shows the
