Patent Application
20070212787
This invention relates generally to quantitative chemical analysis. More particularly, this invention relates to quantitative analysis of polymers by energy dispersive x-ray fluorescence.
Legislation in the European Union (EU) has been enacted to reduce the level of hazardous chemicals in the environment. The Restriction of certain Hazardous Substances (ROHS) act has targeted materials such as lead, cadmium, mercury, chromium VI and some brominated flame retardants used in electronic devices. In order to comply with these enacted regulations, a method to detect and identify these and other hazardous chemicals in electronic devices is needed. Such a method should be fast and accurate to enable rapid testing and short turnaround times in keeping with the ‘time to market’ requirements of the global electronics industry. The detection method also needs to be highly cost effective and it should not have any adverse impact on the environment by using other hazardous substances in the detection procedure.
Prior art methods for analysis of trace amounts of metals in polymers have focused on methodologies such as wet digestion (microwave, sulfuric acid digestion, etc.) or by the well-known internal standard or external standard techniques using commercial standards. Although these methods are time-tested and internationally accepted, they are time consuming and costly, and require sophisticated sample preparation and measurement.
The accompanying FIGURE, which together with the detailed description below are incorporated in and form part of the specification, serves to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.
As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The terms a or an, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language).
A method of quantitatively measuring trace amounts of metals in polymer samples uses energy dispersive x-ray fluorescence (EDXRF) spectrometry to fluoresce and detect metals that are present in the polymer sample. The polymer sample is ground to a powder and formed into a thin film by heat and pressure. The film is then analyzed using EDXRF, and the data representing the amounts of the various metals present in the sample is multiplied by one or more correlation factors that have been determined from measurement of characterized polymers that have similar composition to the polymer sample and that bracket a range of metal concentrations in the sample.
Referring now to
A more accurate determination of the actual amount of the various metals in the polymer sample present in weight percent is obtained by multiplying the data 40 that is representative of the amount of x-rays collected for each element by one or more correlation or calibration factors 50. These factors are determined by measurement of known, characterized polymers that have similar composition to the polymer sample and that bracket a range of metal concentrations in the polymer sample. This, of course, requires that one knows the identity or type of polymer(s) present in the polymer sample. The identity of the polymer sample can be obtained in a number of ways, and although it can be identified at any point in the procedure prior to measuring 50, we find it most convenient to identify the polymer at the beginning of the analysis, that is, prior to grinding to a powder 10. The identity of the polymer can be determined 60 by infrared spectroscopy analysis, other well-known laboratory analysis methodologies, it may already be known by the analyst, or the identity can be provided by others (such as the manufacturer of the polymer). The plurality of calibration factors obtained on the known polymer samples can be combined into one or more calibration curves that plot, for example, weight percentage of a detected metal as a function of the information provided by the EDXRF spectrometer.
In summary, without intending to limit the scope of the invention, trace amounts of metals present in polymers can be accurately determined according to a method consistent with certain embodiments of the invention by forming a thin film of the sample under heat and pressure, analyzing the film using EDXRF, and multiplying the data representing the amounts of the various metals present in the sample by one or more correlation factors that have been determined from measurement of characterized polymers that have similar composition to the polymer sample. While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those of ordinary skill in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.
