209 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1994 VOL. 9 Determination of Extractable Organic Chlorine by Electrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry* Pentti K. G. Manninen VTT Reacfor Laboratory P.O. Box 200 Fin42151 Espoo Finland Extractable organic chlorine (EOCI) is a sum parameter used to describe the organic chlorine concentration in solid or liquid samples that can produce injurious effects on health. In this work a new method is presented for the determination EOCI. Inductively coupled plasma mass spectrometry (ICP-MS) is not especially suitable for the determination of chlorine owing to the high ionization energy of chlorine. However when electrothermal vaporization (ETV) is compared with ICP-MS the sensitivity is high enough to facilitate sum parameter analysis from limited sample volumes.Ethyl acetate has been used as an extraction solvent. Chlorine was determined by collecting data during heating by monitoring mlz 35 using the single-ion monitoring mode. The detection limit for EOCl by ETV-ICP-MS is approximately 10 ng. Keywords Extractable organic chlorine; electrothermal vaporization ; inductively coupled plasma mass spectrometry Extractable organic chlorine ( EOCl) the lipophilic fraction of total organic chlorine (TOCl) can be characterized as that part of organically bound chlorine which can be separated from a sample matrix by using an organic water-immiscible solvent extraction procedure. In recent years several methods have been developed for the determination of EOCI especially for environmental research.lP4 Mainly because most of the known organic chlorine compounds such as chlorinated biphenyls ( PCBs) dibenzodioxins and phenols are generally considered as harmful or dangerous substances.Most of these methods use a microcoulometer or neutron activation analysis (NAA) as the detection method. Typical solvents are light petroleum (b.p. 40-60 "C) disopropyl ether pentane hexane cyclohexane and ethyl acetate. In this work a new detection method for EOCl is presented. Inductively coupled plasma mass spectrometry (ICP-MS) is not especially suitable for the determination of chlorine owing to the high ionization energy of chlorine. The detection limit for chlorine is > 10 pg 1-' compared with detection limits of < 1-10 ng 1-' for most other elements.However when electro- thermal vaporization (ETV) which was first introduced by Gray and Date,' is combined with ICP-MS the detection capability for the absolute amount of chlorine from limited sample volumes is increased. Sample introduction by ETV has several advantages over solution nebulization:6 for example a reduction in matrix and spectral interferences higher analyte transport efficiency because all of the vaporized sample is transported to the plasma small sample volume requirement and most importantly here the ability to analyse organic solvents directly. Recently Richner and Wunderli7 used the ETV-ICP-MS technique for determining polychlorinated biphenyls (PCBs) in oil. They have shown that it is possible to separate organic and inorganic chlorine by modifying the heating profile and even separate PCB isomers to some extent. Experiment a1 Equipment A Fisons PlasmaQuad PQ 11+ with a Fisons ElectroThermal Vaporizer ETV Mk I11 were used in this work.The operating conditions are listed in Table 1. The pyrolytic graphite coated graphite furnace tubes were from Ringsdorf-Werke The graphite furnace and the plasma torch were connected with clear nylon tubing (80 x 0.4 cm). Mass calibration and response * Presented at the XXVTII Colloquium Spectroscopicum Internationale (CSI) York UK June 29-July 4 1993. Table 1 Operating conditions Parameter R.f. power/W Outer gas flow rate1 min-' Intermediate gas flow rate/l min- Nebulizer gas flow rate/l min-' Dwell time per channel/ms Acquisition time/s Single-ion monitoring mode m/z Heating programme Time/s 0-60 60-65 65-80 80-90 Value 14 1 350- 1450 0.9 0.5-0.6 50 60 35 Temperature/"C 20- 100 100- 1000 1000-2600 2600 calibration were carried out by introducing a 100 pg I-' solu- tion (Be Co In La Pb Bi U) by the conventional solution nebulizing system consisting of a Gilson Minipuls 3 peristaltic pump V-groove De Galan nebulizer a Scott-type quartz spray chamber and a Fassel-type quartz torch.After tuning the nylon tube was connected between the torch and the graphite furnace and the torch position was re-checked by injecting a 10 mg 1-' solution of Hg into the furnace and monitoring the '"Hg signal without heating. Usually only a slight adjustment of the position of the torch was needed. Portions (10-50 pl) of sample solution were injected manually into the graphite tube and the dosing hole was closed with a carbon rod before the heating sequence was started.The data were collected by monitoring m/z 35 using the single-ion monitoring (SIM) mode during heating. The typical heating profile and acquiring time are presented in Fig. 1. Data were also collected at least once in every working period by scanning the mass range m/z 34-36 to check that the mass calibration which must be very precise in the SIM mode was stable. The EOCl results obtained by ETV-ICP-MS were compared with those obtained by NAA which was used for chlorine determination during the extraction procedure. Samples were irradiated in the Triga Mark I1 reactor in the 4 x 10'' n cm-2 s-' neutron flux using sealed polyethene cap- sules which were transferred to the reactor by a pneumatic transfer system.Chlorine was analysed by measuring a photo- peak at 1642 keV using a Ge(Li) detector and a Canberra MCA 40 multichannel analyser. A more detailed description of the method is published210 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1994 VOL. 9 400 ,K! 300 8 3 0 5 200 or 100 1000 2600 20 4000 3000 2000 1000 0 Heating te m pe ra t u re/" C Fig. 1 Signal from (a) an ethyl acetate blank (b.p. 77 "C) and (b) a TCA standard (8 mg l-' b.p. 198 "C). Injection volume 20 p1 Reagents Analytical-reagent grade ethyl acetate (Baker) was used. Organic chlorine compounds which were used during the development and testing of the method were trichloroacetic acid (TCA Merck) pentachlorophenol (PCP EPA) 0- chlorobenzoic acid (CBzA Merck) and p-chloroanisole (CAn Fluka).Purified water was produced by the Millipore R04+Milli-Q system and nitric acid was pro analysi grade (Merck). Standard solutions of TCA (3 6 9 and 12mg1-I) were prepared in ethyl acetate. Procedure For solid samples the procedure was as follows. Sample ( NN 1 g) was extracted with 20ml of ethyl acetate under reflux for 30min. The extract was cooled in a cold water-bath and cleared by centrifugation. Liquid samples (5-20 ml) were extracted with 20 ml of ethyl acetate. All extracts were washed with 20-50 ml of purified water to remove inorganic chloride. The extracts were then stored in a freezer (-18°C) where water was separated from ethyl acetate as small ice pearls.The true amount of extract can be determined after filtration of the ice pearls. The extracts can be injected into the ETV- ICP-MS without any further treatment. The injected volumes varied from 10-5Opl depending on the type of sample and experiment. The data were collected during the heating period as shown in Fig. 1. The peak area was used for calculations. After every third or fifth sample 50 pl of 1% nitric acid were injected into the graphite tube and the heating profile was run. This procedure was necessary for the removal of carbon deposits which result in a reduction of the signal intensity from the sample cone. For NAA 2-3 ml of extract were put into the polyethene capsules which were sealed in plastic bags. These bags were put into liquid nitrogen before irradiation.After irradiation for 1 min the extracts were melted in a hot water-bath and 1 ml of extract was transferred to a clean capsule for measurement. Results and Discussion Ethyl acetate was selected as the organic solvent because of its high extraction power and applicability especially for sediment sarnple~.~*'~ The mean extraction efficiencies for the organic chlorine compounds tested were 91% for TCA 87% for CBzA and 107% for PCP. Another advantage of ethyl acetate is the very low chlorine background which facilitates its use without any pre-distillation or other purification procedure. Several heating profiles were tested and the slowly rising temperature programme was chosen for the determination of chlorine. With this programme the organically bound chlorine was separated very cleanly from the somewhat noisy signal coming from the vaporization step where the temperature is about 2600°C.Ethyl acetate was gently removed by heating the tube to 100°C over a period of 1 min. The temperature was then raised to 1000°C in 5 s. During this step all the organic chlorine compounds tested were vaporized and trans- ferred to the plasma where atomization and ionization of the element occurs. The organic load from the solvent and the sample did not noticeably affect the energy consumption of the plasma. Some carbon deposits from the solvent were found to build up especially on the sampler cone after 3-5 sample injections. Injection of 50 pl of 5% nitric acid efficiently removed the black deposits and therefore this procedure was repeated after every 3 or 5 samples.Problems were also associated with carbon deposits inside the connection tube between the ETV and the plasma torch. These deposits decreased after carefully readjustment of the temperature Cali- bration of the instrument. In Fig. l(a) the signal obtained from an ethyl acetate blank is shown. In Fig. 1 (a) and (b) the x-axis presents the data- acquisition time during the heating cycle. The temperatures reached are labelled on these axes rather than time in order to give a better view of what is happening during the heating. A small peak with a net area of about 900 counts is observed a few seconds after the start of the heating step from 100 to 1000 "C. This corresponds to a time of 62-63 s. A more noisy signal pattern is observed when the furnace temperature reaches its highest values.During this step the furnace was cleaned and a signal from inorganic chloride solutions (NaCl) was obtained. Hence if an inorganic chloride is present in an injected sample it is well separated from organic chlorine and does not disturb the determinations of EOC1. This has also been reported by Richner and W~nderli.~ In Fig. l(b) there is a clear peak from TCA (8 mg 1-' injection volume 20 pl). The limit of detection (LOD) for EOCl by ETV-ICP-MS is greatly dependent on the tuning of the instrument. A well- known problem is how to get a stable and sufficiently long signal for tuning the lens system and for centralizing the torch position when one is working with the ETV. Owing to these difficulties the chlorine response normally varied in the range 105-106 counts pg-'.The calibration line was linear (r=0.99) the slope was 12900 and the intercept was -3600. In this experiment the ethyl acetate blank value was 14 100 & 2500 counts. Using the formula LOD = 3sb an LOD of 10 ng was obtained for chlorine. This is an acceptably good value despite the fact that the repeatability is not very good. The relative standard deviation (RSD) for TCA standards is normally about 5% but for real extracts it usually varies from 5 to 30%. The organic chlorine compounds were then extracted into ethyl acetate and the EOCl concentrations were deter- mined by NAA p-chloroanisole (EOC134 mg 1-') pentachlor-JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1994 VOL. 9 21 1 Pent ac h I o ro p h e n o I Trichloroethene pChloroanisol 0-C h I o ro benzo ic acic Organic chlorine compound Fig.2 Integrated peak areas divided by chlorine content of some organic chlorine extracts. The true absolute amount of chlorine is determined by NAA. The response to chlorine was of the same order of magnitude for all of these compounds ophenol (EOCl 8 mg l-') trichloroethene (EOC1 6 mg 1-I) and o-chlorobenzoic acid (EOC1 3 mg 1-'). The integrated counts pg-' of C1 have been determined by ETV-ICP-MS (Fig. 2). Each determination was repeated 3-5 times. The results show that a moderately good response and repeatability can be achieved using ETV-ICP-MS for the determination of chlorine with these compounds which each represent a differ- ent stage of chlorination.The method was also applied in the analysis of a real sediment sample from the Gulf of Bothnia (EOCl 570 pg 8-I dry mass by NAA). The ETV-IPC-MS result was slightly higher (165000f38000 RSD 23% n = 5 ) than for the test compounds indicating some matrix effect. These results are just tentative and the existence and nature of the matrix effects have not been investigated thoroughly. Conclusion Although the method discussed here is not a standard pro- cedure the possibility of its use in the determination of EOCl is clearly demonstrated. The technique is sensitive enough compared with conventional microcoulometer or NAA tech- niques and is element selective. These experiments have been carried out without any auxiliary gases or extra valve systems so they should be easily transported and repeated with any similar facilities.Future investigations are needed to assess possible matrix interferences and to improve repeatability. In this experiment it is thought that the poor repeatability and occasional loss of sensitivity could at least partly be attributed to a malfunction of the furnace instrument. References 1 2 3 4 5 6 7 8 9 10 Gron C. Vatten 1988 44 205. Wegmann R. C. C. 'Determination of Organic Halogens' Proceedings of the Second European Symposium on Analysis of Organic Micropollutants in Water Killarney Ireland November Griffin H. C. Copeland R. A. Epstein P. Harger R. and Wade D. R. Radiochem. Radioanal. Lett. 1981 50 67. Riggin R. M. Lucas S . V. Jungclaus G. A. and Billets S. J. Test. Eval. 1984 12 91. Gray A. L. and Date A. R. Analyst 1983 108 1033. Gregoire D. C. Lamoureux M. Chakrabarti C. L. Al- Maawali S. and Byrne J. p. J. Anal. At. Spectrom. 1992 7 579. Richner P. and Wunderli S. J. Anal. At. Spectrom. 1993 8 45. Manninen P. Ann. Acad. Sci. Fenn. Ser. AZZ. No. 225 1990. Manninen P. K. G. and Hasanen E. J. Radioanal. Nucl. Chem. 1993,167 353. Makinen I. Poutanen E.-L. and Manninen P. The Science of the Total Environment Elsevier Amsterdam in the press. 17-19 1981 pp. 249-263. Paper 3103891 B Received July 6 1993 Accepted October 7 1993