Low-level determination of non-metals (Cl, Br, I, S, P) in waste oils by inductively coupled plasma optical emission spectrometry using prominent spectral lines in the 130–190 nm range K. Krengel-Rothensee, U. Richter and P. Heitland* Spectro Analytical Instruments GmbH, Boschstr. 10, D-47533 Kleve, Germany Received 8th September 1998, Accepted 12th February 1999 The non-metals Cl, Br, I, S and P were determined in waste oils by inductively coupled plasma optical emission spectrometry (ICP-OES).Prominent spectral lines in the vacuum ultraviolet spectral region between 130 and 190 nm were applied simultaneously with a nitrogen-filled Spectro polychromator. For example, the intense spectral lines for chlorine (Cl 134.72 nm), bromine (Br 163.34 nm), iodine (I 161.76 nm), sulfur (S 180.70 nm) and phosphorus (P 177.50 nm) were used. The detection limits of Cl, Br, I, P and S in undiluted waste oils are 0.9, 1.6, 0.47, 0.04 and 0.07 mg kg-1, respectively. To achieve these detection limits the standard oils and samples were diluted 1+4 (m/m) with kerosene.For the analysis of waste oils, small amounts of oxygen (80 ml min-1) were added to the outer plasma gas. In order to establish optimized plasma operating conditions for non-metals, a simplex optimization was performed. Compared with metals such as Ba, V, Cd, Al or Ni, a lower nebulizer gas flow and a higher generator power is advantageous to improve the detection limits for the non-metals.Because the detection limit for Cl is more than a factor of 1000 below tolerated limits of waste oil regulations, highly viscous oils could be analyzed after a suitable dilution with kerosene. The determination of the total Cl concentration by ICPOES can be used as a means of screening for the highest possible concentration of polychlorinated biphenyls (PCBs) in waste oils. or metallic surfaces in the refining process by impurities. Oil Introduction additives (b) often have the task to enhance the lifetime of an The determination of non-metals in organic samples with ICP oil and must be controlled precisely.Therefore, the use of an optical emission spectrometry (ICP-OES) has increasingly internal standard is often necessary.Wear metal concentrations become a point of interest since intense spectral lines for non- in (c) lubricating oils are determined as an indicator for metals in the vacuum ultraviolet wavelength region below bearing wear in engines.Monitoring wear metals ensures the 190 nm can be used with ICP spectrometers. In this wavelength reliability of engines and optimizes servicing periods. When region are prominent spectral lines for many environmentally analyzing (d) waste oils the determination of heavy metals, or industrially important elements for ICP-OES.1–3 Examples halogens and sulfur has become an environmental analytical are aluminum (167.08 nm), boron (182.64 nm), bromine task for ICP spectrometry.In particular, the determination of (154.07), chlorine (134.72 nm), lead (168.21), mercury Cl is of great interest in environmental element analysis, (184.84 nm), nitrogen (149.25 nm), sulfur (180.73 nm) and because of the hazardous potential of chlorinated organic phosphorus (177.50 nm). compounds, such as polychlorinated biphenyls (PCBs), penta- Because wavelengths below 200 nm are absorbed by oxygen chlorophenol (PCP), polychlorodibenzodioxins (PCDDs) or or water vapour, spectrometers were evacuated or purged.polychlorodibenzofurans (PCDFs). Vacuum optical systems for ICP spectrometry have the prob- Apart from halogen determination in waste oils, the lem that they are often not able to attain a perfect vacuum determination of PCBs is often required. In the past, PCBs and that back-streaming vapours from the oil-filled vacuum have been used in various technical applications, i.e., in pumps cause coatings on the optical surfaces of the spec- electrical transformers or capacitors, because of their chemical trometer.1 A successful approach to avoid these disadvantages and physical properties, such as thermal stability, low flammis a nitrogen-filled optical system.This technique allows ability and low conductivity. Since it was shown that PCBs element determinations down to a wavelength of 120 nm. are carcinogenic and persistant, their use was limited. Today, A wide range of organic samples are analyzed by ICP the production and import of PCBs is prohibited in many spectrometry, such as solvent extracts, chromatography countries, but waste oils will still be the main source for PCBs eZuents or the organic solutions themselves.Therefore, the in the future. The recycling and disposal of waste oils is characteristics of an ICP operating with organic aerosols were regulated by the metal, the halogen and the PCB content in studied in several papers.4–9 However, the majority of organic many countries. In the US, waste oil containing more than samples are various oils such as crude oils, lubricating oils, 0.1% (m/m) of Cl is considered to be hazardous waste. In refined oils or waste oils.Typical examples of ICP applications Germany,22 the tolerance limit for the total Cl content in are the determination of (a) impurities in crude oils or refined waste oils is 0.2% (m/m) and the tolerance limit for PCBs is oils, (b) additives in oils or in gasoline, (c) wear metals in 20 mg kg-1.PCB analysis by gas chromatography with mass lubricating oils, or (d) elements in waste oils.10–21 Monitoring spectrometric or electron-capture detection is often time conof (a) crude oils or refined oils, for instance, could be required suming and therefore rapid screening tests for PCBs are useful.23 to characterize the oil itself or to avoid destruction of catalysts J. Anal. At. Spectrom., 1999, 14, 699–702 699This paper describes the determination of non-metals in oils PCBs, diVerent weighed portions of Arochlor 1260 were diluted to 2 g with the base oil and made up to 5 g with using prominent spectral lines in the vacuum ultraviolet spectral region down to Cl 134.72 nm.The optimization of the kerosene at room temperature. ICP operating conditions for the non-metals compared with some metals was performed and the detection limits in oils for Results and discussion new prominent spectral lines in routine analysis were calculated.Further, ICP-OES was investigated as a screening test For non-metals such as Cl, Br, I, N, P and S the most intense spectral lines are in the vacuum ultraviolet spectral region for the highest possible PCB concentration in waste oils calculated from the total Cl concentration because total Cl below 190 nm. Typical examples of these spectral lines are given in Table 2. The measured intensity of the most intense can be determined at low ppm levels in oils.spectral line for each element in Table 2 is standardized to 100. Several of the spectral lines in Table 2 have not been Experimental discussed in the literature in combination with ICP-OES for routine analysis. For Cl, which is environmentally one of the Apparatus most important elements to be determined in organic The investigations described below were performed using a compounds, the intense spectral line at 134.72 nm was used. Spectro ICP (Spectroflame Compact E, Spectro Analytical When analyzing organic samples with ICP-OES sometimes Instruments, Kleve, Germany) with a free-running 27.12 MHz the addition of oxygen is required.Reasons for oxygen addition generator. For sample introduction, a cross-flow nebulizer are (a) the prevention of carbon deposits on the injector quartz (Spectro) was used in combination with a Scott-type double tube or (b) the minimization of spectral interferences by pass spray chamber. Because of the excellent plasma stability carbon or carbon molecules (C, CH, C2, etc.).In Fig. 1 the for all samples a cooled spray chamber for oil analysis was eVect of adding small amounts of oxygen to the outer gas on not required. Small amounts of oxygen (80–240 ml min-1) the background equivalent concentration (BEC) for diVerent were added to the outer plasma gas to avoid carbon deposits metals and non-metals is shown. The BEC was calculated on top of the quartz injector tube. Further ICP operating from BEC=c/SBR, where c is the concentration of the conditions are described in Table 1.elements in the oil standard and SBR the signal-to-background The polychromator optics of the ICP spectrometer are ratio. The BECs for the elements are displayed in Fig. 1 as enclosed in a chamber filled with nitrogen to slightly above relative values. For the non-metals Cl, Br, I and S, oxygen atmospheric pressure. By the use of a membrane pump the addition was found to cause an overall increase in the BEC nitrogen filling gas is circulated through a filter which removes [Fig. 1(a)]. Similarly, the BEC of the metals is significantly oxygen, water vapour and other species that might absorb increased on adding oxygen to the outer gas, except for Na electromagnetic radiation. This ensures the best possible light [Fig. 1(b)]. Hence, oxygen addition is disadvantageous for the transmission in the wavelength range down to 120 nm and in limits of detection for all the determined elements with the addition the optical system is protected from contamination.exception of Na. The main spectral line of Na (Na I 589.59 nm) The use of a nitrogen-filled spectrometer saves costs compared in oil analysis is aVected by a carbon emission. The improved with nitrogen-flushed systems. values of the BEC for Na are due to a reduced carbon spectral interference on adding oxygen. Line selection The eVect of the nebulizer gas flow on the relative BEC values of the elements is shown in Fig. 2. The optimum BEC The non-metals determined in oils were Cl, Br, I, P and S at (the lowest BEC) for the non-metals Cl, Br, I and S is achieved 134.72, 163.34, 161.76, 177.50 and 180.73 nm, respectively. at 0.5–0.6 l min-1 [Fig. 2(a)]. For the elements Al, Ba, Cd, Ni Metals determined were Al, Ba, Cd, Ni and V at 308.21, and V, a higher nebulizer gas flow of 0.9–1 l min-1 is advanta- 455.40, 226.50, 231.60 and 292.46 nm, respectively. Sample preparation Table 2 Prominent non-metal spectral lines below 190 nm.a Spectral line intensities were measured with the described instrument A 0.1–1 g amount of the standard oils (Alpha Resources, Stevensville, MI, USA) or 1 g of the sample was made up to Element Line/nm Relative intensity 2 g with a base oil (Conostan, Ponca City, OK, USA) and Cl 134.72 100 then diluted to 5 g with kerosene (Sigma-Aldrich, Steinheim, 135.16 35 Germany) at room temperature.The base oil and kerosene 136.34 30 were applied to compensate for diVerences in the viscosity of Br 148.84 90 sample and standard solutions. 153.17 26 The PCB samples were prepared from Arochlor 1260 154.07 100 157.48 10 (Promochem, Wesel, Germany), and were diluted 1+9 (m/m) 163.34 12 with kerosene at 40 °C. Arochlors were the most widely used I 142.56 75 industrial PCBs. The Arochlor 1260 sample is a reference 158.27 50 material for the analysis of PCBs with a Cl concentration of 161.76 95 60% (m/m). For the measurements of the Cl recoveries in 179.91 85 183.04 100 N 149.26 100 Table 1 ICP operating conditions 174.27 40 174.52 20 Generator Free-running at 27.12 MHz P 177.50 100 Power/W 1200 178.29 75 Nebulizer ‘Cross-flow’ (Spectro) S 166.67 10 Spray chamber Double pass, Scott-type 180.73 100 Outer gas/l min-1 12 182.04 75 Intermediate gas/l min-1 2 182.62 25 Nebulizer gas/l min-1 0.9 Nebulizer pressure/bar 3.1 aAll intensities are standardized to the most intense line of that Sample uptake rate/ml min-1 0.8 particular element. 700 J. Anal. At. Spectrom., 1999, 14, 699–702Fig. 1 EVect of added oxygen to the outer gas on the BEC for Fig. 3 EVect of the generator power on the BEC for diVerent nondi Verent non-metals (a) compared with some metals (b): A, S metals (a) compared with some metals (b): A, S; B, Br; C, I; D, Cl; 180.7 nm; B, I 161.7 nm; C, Br 163.3 nm; D, Cl 134.7 nm; E, Cd E, V 292.5 nm; F, Ba; G, Al; H, Cd; I, Ni. Wavelengths as in Fig. 1. 226.5 nm; F, V 292.5 nm; G, Al 308.2 nm; H, Ba 455.4 nm; I, Ni 231.6 nm; J, Na 589.59 nm.higher generator power seems to be advantageous for the determination of halogens and sulfur with higher excitation energy for their spectral lines compared with the determined metals Al, Ba, Cd, Ni and V. Thus, for the simultaneous determination of non-metals and metals, compromise ICP operating conditions should be selected. For the determination of Cl, Br, I and S, a higher generator power and a lower nebulizer gas flow is required to improve the limits of detection for these elements.Followed by univariate searches for the optimum values of power, nebulizer gas flow and additional oxygen gas flow, a multivariate simplex optimization was used to establish the optimum plasma parameters for a low BEC of Cl. The parameter ranges for the power, nebulizer gas flow and additional oxygen gas flow are 1000–1600 W, 0.4–1.2 l min-1 and 80–240 ml min-1, respectively. For the simplex procedure the power, nebulizer gas and added oxygen used were varied in steps of 100 W, 0.1 l min-1 and 80 ml min-1, respectively.The lowest value for the BEC of Cl was achieved at 1500 W generator power, 0.6 l min-1 nebulizer gas flow and 80 ml min-1 additional oxygen flow to the outer plasma gas. In comparison with Cl, the lowest BEC of the metals V, Ni and Cd was found at 1200 W, 0.9 l min-1 and 80 ml min-1 after simplex optimization. Table 3 lists the detection limits for non-metals and metals in oil.The detection limits were calculated from the standard deviation (3s) of ten measurements of the blank solution (base oil/kerosene). The detection limits for the non-metals Cl, Br, Fig. 2 EVect of the nebulizer gas flow on the BEC for diVerent nonmetals (a) compared with some metals (b): A, S; B, Br; C, I; D, Cl; I, S and P in the undiluted oil are 0.9, 1.6, 0.47, 0.07 and E, Al; F, V; G, Ba; H, Cd; I, Ni. Wavelengths as in Fig. 1. 0.04 mg kg-1, respectively.The detection limit for Cl (0.9 mg kg-1) is more than a factor of 2000 below the tolerated limit stated in the German waste oil regulations geous [Fig. 2(b)]. This eVect could be caused by the higher excitation energy of the non-metals compared with the metals (2000 mg kg-1). Therefore, it is possible to analyze highly viscous oils using suYcient dilution with kerosene to adjust for the applied spectral lines. As shown in Fig. 3 there is also a diVerence in the eVect of the viscosities of samples and standards. The following example discusses the ability of ICP-OES to the generator power on the relative BECs of the non-metals and metals.For Cl, Br, I and S, the lowest BECs are achieved monitor the maximum PCB content in waste oils by the determination of Cl. It is assumed that the Cl concentration at 1400–1600 W [Fig. 3(a)], while the lowest BECs for Al, Ba, Cd, Ni and V are in the range 1200–1300 W [Fig. 3(b)]. A in a PCB mixture is 50% (m/m).This assumption may be J. Anal. At. Spectrom., 1999, 14, 699–702 701Table 5 Comparison of certified and experimentally determined Cl Table 3 Detection limits (LOD) of the elements in the undiluted oil after simplex optimization of the ICP operating conditions for Cl contents in Arochlor 1260 samples diluted with a base oil and kerosene 134.724 nm (power: 1500 W, nebulizer gas: 0.6 l min-1, O2 additional gas: 80 ml min-1). The oil samples were diluted 1+4 (m/m) with kerosene for analysis Sample 1 2 3 PCB concentration/mg kg-1 1.77 16.13 32.68 Metals Non-metals State of ionization Line/nm LOD/mg kg-1 Certified Cl concentration/mg kg-1 1.06 9.68 19.61 Determined Cl concentration/mg kg-1 1.08 9.63 19.28 Al I 308.21 0.15 Ba II 455.40 0.003 Relative standard deviation (%) 4.8 1.6 0.9 Cl recovery (%) 101.8 99.5 98.3 Br I 163.34 1.6 Cd II 226.06 0.009 Cl I 134.70 0.9 I I 161.76 0.47 result in this concentration range.Consequently, ICP-OES is Na I 589.59 0.08 suitable as a fast screening test of the highest possible PCB Ni II 231.60 0.012 concentration calculated from the total Cl concentration to P I 177.50 0.04 monitor limiting values of PCBs in waste oils.S I 180.73 0.07 V II 292.46 0.018 Conclusions Using a nitrogen-filled spectrometer, ICP-OES provides the regarded as practical because the Cl concentration in PCBs ability to determine the non-metals Cl, Br, I, S and P at their for technical applications is between 30 and 60% (m/m) with intense spectral lines in the range 130–190 nm.These non- the higher concentrations being preferred. In Table 4 the PCB metals and a few metals in oils were determined simultaneously isomers are listed according to their Cl concentration. The with a nitrogen-filled polychromator. In particular, the deter- mean value for the Cl concentration in a PCB isomer is 52.8%. mination of Cl in organic waste oils is of great environmental If the Cl concentration in the PCB mixture is 50% (m/m), interest because of the hazardous potential of chlorinated then 20 mg kg-1 PCB of this mixture in an oil corresponds to organic compounds such as PCBs, PCDDs and PCDFs.The 10 mg kg-1 Cl. This is more than a factor of 10 higher than problem of determining these hazardous organochlorine com- the above-determined detection limit for Cl in oil. The pounds will be one of the important analytical tasks of the requested limiting value according to the German waste oil future.Because of the low detection limits for the halogens at regulations22 is 20 mg kg-1 PCB. Thus, a fast screening test spectral lines down to 134.7 nm for Cl, the determination of for the highest possible PCB content in waste oils calculated halogens in waste oils can be performed with ICP-OES. from the Cl concentration can be accomplished with ICPFurther fast screening tests for an upper limit of the PCB OES, even if the determination of the total Cl content in waste concentration calculated from the Cl concentration are possible oils does not necessarily determine the PCB content.A reliable with ICP-OES. statement of the PCB concentration calculated from the total Cl concentration could not be given, but it is possible to state whether a limit value for PCBs in waste oil regulations (a) References might be exceeded or (b) is in no case exceeded. In the first 1 V. B. E. Thomsen, G. J. Roberts and D. A. Tsourides, Int.Lab., case (a) further PCB analyses should be conducted, but in the 1997, 27, 9A. second case (b) no further eVorts are required to show that 2 J. Alvarado and J. W. Carnahan, Appl. Spectrosc., 1993, 47, 2036. the PCB concentration is below a limiting value. Therefore, 3 D. D. Nygaard and D. A. Leighty, Appl. Spectrosc., 1985, 39, 968. quantitative PCB determination by GC-MS which often 4 C. Pan, G. Zhu and R. F. Browner, J. Anal. At. Spectrom., 1990, requires time consuming sample preparation may be avoided, 5, 537.resulting in considerable savings of time, personnel and 5 A. W. Boorn and R. F. Browner, Anal. Chem., 1982, 54, 1402. 6 A. W. Boorn, M. S. Cresser and R. F. Browner, Spectrochim. expenditure. Acta, Part B, 1980, 35, 823. To verify the applicability of the Cl determination in PCBs, 7 M. W. Blades and B. L. Caughlin, Spectrochim. Acta, Part B, the technically applied PCB mixture Arochlor 1260 containing 1985, 40, 579. 60% (m/m) Cl was analyzed at three diVerent dilution levels 8 D.G. Weir and M. W. Blades, J. Anal. At. Spectrom., 1994, with base oil and kerosene as described above. Table 5 lists 9, 1323. the experimentally determined Cl concentration compared 9 D. G.Weir and M. W. Blades, J. Anal. At. Spectrom., 1996, 11, 43. 10 R. I. Botto and J. J. Zhu, J. Anal. At. Spectrom., 1996, 11, 675. with the certified Cl concentration in Arochlor 1260. Although 11 P. N. Bangroo, C. R. Jagga, H. C. Arora and G.N. Rao, At. sample 1 was analyzed close to the detection limit, the recover- Spectrosc., 1995, 16, 118. ies and the relative standard deviation were satisfactory. The 12 X. R. Liu and G. Horlick, J. Anal. At. Spectrom., 1994, 9, 833. relative standard deviation for the Cl concentration in the 13 M. Bettinelli and P. Tittarelli, J. Anal. At. Spectrom., 1994, 9, 805. diluted PCBs is in the range 0.9–4.8% and represents a good 14 R. I. Botto and J. J. Zhu, J. Anal. At. Spectrom., 1994, 9, 905. 15 M. Murillo and J. Chirinos, J. Anal. At. Spectrom., 1994, 9, 237. 16 M. Murillo, A. Gonzales, A. Ramirez and N. Guillen, At. Table 4 Chlorine concentration in PCB isomer groups Spectrosc., 1994, 15, 90. 17 M. Murillo, N. Carrion and J. Chirinos, J. Anal. At. Spectrom., Number Cl concentration 1993, 8, 493. PCB Formula of isomers (%) 18 R. I. Botto, J. Anal. At. Spectrom., 1993, 8, 51. 19 R. I. Botto, Spectrochim. Acta. Rev., 1991, 14, 141. Monochlorobiphenyl C12H9Cl 3 19 20 J. D. Algeo, D. R. Heine, H. A. Phillips, F. B. G. Hoek, Dichlorobiphenyl C12H8Cl2 12 32 M. R. Schneider, J. M. Freelin and M. B. Denton, Spectrochim. Trichlorobiphenyl C12H7Cl3 24 41 Acta, Part B, 1985, 40, 1447. Tetrachlorobiphenyl C12H6Cl4 42 49 21 J. L. Fabec and M. L. Ruschak, Anal. Chem., 1985, 57, 1853. Pentachlorobiphenyl C12H5Cl5 46 54 22 Alto�lverordnung, (BGBl 1), 1987, 2335. Hexachlorobiphenyl C12H4Cl6 42 59 23 P. Richner and S. Wunderli, J. Anal. At. Spectrom., 1993, 8, 45. Heptachlorobiphenyl C12H3Cl7 24 63 Octachlorobiphenyl C12H2Cl8 12 66 Nonachlorobiphenyl C12H1Cl9 3 69 Paper 8/07024E Decachlorobiphenyl C12Cl10 1 71 702 J. Anal. At. Spectrom., 1999, 14, 699–7