By Sylvain Lévesque, Centre d'Expertise en Analyse Environnementale du Québec and Nigel Cocks, Hewlett-Packard (Canada) Ltd.

PCBs are among many environmental pollutants routinely analyzed. Originally created in Aroclor mixtures for use in electrical equipment, their chemical persistence and toxicity requires proper controlled disposal and environmental monitoring.

Figure 1. Results from the standards (calibrated PCB congeners) combined with the found components (true unknowns) to yield the total distribution of PCB homologues (the sum of one or more possible Aroclors).

The Quebec Ministry of Environment (Canada) has developed a new method for PCB homologue analysis using the HP 5973 GC/MS system and G1701 software. The method uses a selected mix of PCB compounds, together with customized macros and a custom report, to compute PCB totals by the congener method. This approach is an alternative to the Aroclor pattern method but avoids creating and maintaining a large, complex calibration method with more than 130 congeners.

Choosing the Method
The study of PCBs has traditionally used a peak-pattern recognition formula to recognize Aroclors and decide their toxicity level, but natural weathering and mixing of Aroclors has made an effective pattern recognition difficult. A better analysis is obtained grouping the various chlorine congeners by homologue and identifying them individually. The challenge is that there are 209 possible congener isomers, and tracking all of them is a formidable job.

The standard approach would require creating complex standards with 130+ components in an extensive method capable of quantitating each of these components. While this method is possible, creating and maintaining it and preparing the required complex standards makes it a challenge for routine analysis.

Could there be a better way? Why not create a less complex method using some specific PCB congeners and, without having to know where they are in the data file, have the software locate the rest? Since the current software requires identifying information (e.g., retention time), we have had to create a series of custom macros to bypass this requirement.

Figure 2. Graphical output from the custom report shows distribution of the calibrated congener components in the sample. These results, combined with the true unknown components, provide the totals in Figure 1.

Keeping Track of PCBs In the early 1930's, the use of polychlorinated biphenyls (PCBs) as an insulating and cooling fluid in electrical transformers had been hailed as a significant engineering advance. PCBs replaced the flammable oils that had proven too hazardous to use inside buildings. Only relatively recently were the toxic properties of PCBs fully recognized, but by now they had been used in a variety of other applications, such as hydraulic fluids, and discarded indiscriminately for decades. The further use of PCBs was banned, but the damage had been done: along with other persistent toxic compounds, PCBs have spread throughout the world's marine ecosystems, in part through gradual accumulation in the food chain. PCBs show up in the tissue of fish and marine mammals and are monitored by environmental regulatory agencies throughout the developed world. PCBs come in many groups of compounds identified as Aroclors, each of which contains anywhere from 20 to 45 major PCB congeners. When analyzed with capillary gas chromatography, Aroclors form unique peak patterns that are used for identification. The International Union of Pure and Applied Chemistry (IUPAC) has cataloged the compounds and assigned distinguishing numbers to them. PCBs are not among proven human carcinogens, although there is much evidence of harm to animals. For example, minks feeding on fish in the Great Lakes region of the U.S.A. have suffered reproductive problems. It has also been shown that the ingestion of some PCBs in sufficient doses leads to severe liver damage and death. Because of the known hazards and potential additional ecological detriments, authorities in many parts of the world have established "safe" limits for human consumption. The U.S. Food and Drug Administration, for instance, has set an advisory limit of 2.0 ppm PCBs in commercially traded fish. A new approach to PCB determination from Canada is featured in this issue of PEAK.

Macro Locates True Unknowns
Typically, we prepare a standard mixture of the more important congeners, together with ISTDs and surrogates. The congeners are picked for their toxicity, persistence and abundance in Aroclors. This 41-component mix is run in electron-ion GC/MS SIM acquisition, and a multipoint calibration table is created in the customary fashion. The table is then used by a series of data analysis macros that compute average RRFs, ions and ion ratios from each chlorine congener group.

Figure 3. The total in Figure 1 is often originating from a single or a mixture of PCB Aroclors. Here is one example showing the distribution of calibrated PCB congeners and homologue groups within one Aroclor (1254). Because environmental samples often contain a mixture of Aroclors or weathered Aroclor(s), congener identification offers a better way of summarizing PCB content.

From this information, the macro searches the data file for other PCB congeners that may be present. The resultant report contains both the calibrated components and any others that qualify but are not listed in the table. The results can vary from 50 to 90 components typically, and no two sample reports are alike. The strength of the macros lies in their ability to locate true unknown components; no expected retention time is needed.

Figure 4. Part of the report prepared by the macro. Compounds 1 and 7 are ISTDs. Compounds 2, 3, 4, 5 and 8, 9, 10, 11 are the calibrants. Compounds 6, 12, 13, 14, 15, 16 are true unknown PCB congeners located by the macros. They are grouped by ISTD and added to the results file. This information, together with surrogate recoveries, is passed to the custom report.

The final quantitation report contains all PCB congeners found, grouped by appropriate ISTD. The results file can be checked quickly by the operator (using Qedit) and passed on to a custom report that provides a certificate of analysis, including graphical results.

It is not necessary to calibrate all possible congeners. Once the initial calibration has been completed, samples are run in the usual manner. With the method automatically searching for true unknowns, the operator reviews the data and selects the appropriate reports.

Sample Throughput Quadrupled
We now routinely prepare PCB reports by the congener analysis method using GC/MS and the full power and features of the G1701 data analysis software. The 41-component calibration standard we prepared, coupled with macros and a custom report, produces a complete PCB congener report. The use of macros and a custom report provides an alternative to creating and tracking 130+ component mixtures. By using this method, we were able to increase our sample throughput from five samples to approximately 20 samples a day.

Figure 5. Part of the printout of the PCBs found in the sample. It shows the extracted ions of the PCB congeners and provides a visual picture of PCB components.

Requirements for the Macros When we created the macro for PCB analysis, we needed several features. The macro must provide a report that could be viewed and edited by the operator. average the responses for each congener group and provide an average RRF to quantitate unknowns. Should the operator delete one level for a component, the macro will average with the remaining levels. use ions and ion ratios for target and qualifiers for screening unknowns. As the macros evolved, additional features were included that specify integration events, provide several report styles, and show each congener profile on extracted-ion printouts. As the calibration table is updated, the macros automatically utilize the new information.

References
1. Lévesque, S. and Moore, S. A New Specific Congener Method for the Characterization of Environmental Samples Containing PCBs. Ministère de l'environnement et de la faune du Québec; Centre d'expertise en analyse environnementale du Québec. EnviroAnalysis '98 Conference, held in Ottawa.

2. Méthode d'analyse. Détermination des biphényles polychlorés-Méthode par congénère. (English version available). MA 400-BPC 1.0 1998-05-08; CEAEQ, Ministère de l'Environnement du Québec (1998).