A custom report program for characterizing PCB mixtures.
PCB Reporter integrates a Raw file, applies several Calibration files to the chromatogram, and produces a special report which combines the results. A single analysis may look for up to thirty different Aroclors.
PCB Reporter identifies peaks which contribute to more than one Aroclor, and displays them on a plot, flooded with color. Optionally, reported amounts may be corrected for this source of error. The calculations and the layout of the report are completely under the control of the user. Example files are provided to illustrate the report, and to facilitate the development of your own files.
Automatically generates Bound and ZED files for each Aroclor.
A PCB Primer Polychlorinated biphenyls (PCBs) were once widely used materials. Most uses were banned in 1972, but due to their persistent and toxic nature, it is still necessary to analyze for PCBs." Aroclor" is the Monsanto trade name for their commercial PCB mixtures. The Aroclors are named by appending a four-digit number, e.g. Aroclor-1221, Aroclor-1268. The first two digits represent the number of carbon atoms in the molecule, usually 12 for biphenyl compounds. The last two digits represent the weight percent of chlorine in the mixture. Aroclor 1016 is an exception; in fact it has 12 carbons like the rest, and is 41% chlorine by weight.
Aroclors are made by chlorinating biphenyl until the desired amount of chlorine has been introduced. Therefore they are complex mixtures. There are 209 PCB "congeners". See Table 1 in the appendix.
PCB congeners which lack ortho chlorines can assume a coplaner conformation and are therefore biologically similar to dioxins and dibenzofurans. PCB congeners which contain one or more ortho chlorines assume a staggered conformation and are less toxic. See Table 2 in the appendix.
The Chromatographic challenge
PCB analysis is complicated for many reasons. The primary challenge is that there are a great many very similar compounds. Some congeners are so similar that they co-elute in groups of two or three, even on the best columns.
Aroclor standards are available. The several products are different enough to be separable by chromatography into more or less distinct forests of peaks. However, there is significant overlap (see Tables 3 & 4 in appendix). Most Aroclors contain low levels of just about every congener. Ideally, we could use peak ratios to identify and quantify particular Aroclors. However there are a number of reasons why the "fingerprints" are unreliable.
Variation: Aroclors were produced over many years, and in many factories. Within a particular product, there are significant lot-to-lot variations.
Weathering: PCB is not completely persistent, there are chemical and biological degradation pathways. Some congeners are degraded more rapidly than others. For example, congeners with ortho hydrogens are preferentially metabolized by bacteria.Interference: Many pesticides and herbicides contain chlorine, and some of these co-elute with PCBs.
Crosstalk: Some peaks are characteristic of more than one Aroclor, so when the sample contains both Aroclors, the joint peaks are larger than the other peaks -- in both Aroclors. (See appendix). A practical analysis selects a number of peaks, typically five to eight, which are the largest peaks in the Aroclor standard. Ideally, these are peaks which are both "reliably present" in the samples, and "not present" in other Aroclors. Sometimes even the best choices wind up with two Aroclors looking at the same peak, or peaks.
The PCB Reporter solution
Why is a special utility necessary? Because PCB analysis lies beyond the usual domain.
Chromperfect normally assigns each peak in a chromatogram to at most one component. PCB analysis doesn't "fit" because each Aroclor is in fact a mixture of several congeners, and some peaks are components of more than one mixture. In order to analyze the chromatogram for a number of different mixtures, there must be a Calibration file for each mixture.
PCB Reporter receives the Raw file name from the user. No Method file name is necessary, the one in the Raw file header will be used. There is not much for this “primary” Method file to do, besides control the integration and the appearance of the plots. Since a Method file can only contain one Calibration file name and one Reference file name, it is of no use here. Likewise, any Format file names in the Method file will be ignored.
When it generates a formatted report, Chromperfect normally works with only one Calibration file. But in order to generate its report, Chromperfect must generate certain parts of the report repeatedly, once for each Aroclor. The Format file elements must contain special markings which identify their role in the report.
When PCB Reporter generates its report, it uses the primary Method file, but it overwrites certain settings with the settings from the appropriate Method file