Optics: measuring and testing – By dispersed light spectroscopy – With sample excitation
Patent
1995-03-09
1996-08-13
Evans, F. L.
Optics: measuring and testing
By dispersed light spectroscopy
With sample excitation
356 36, G01N 2131, G01N 2174
Patent
active
055461824
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for the determination of a trace amount of a metal impurity contained in a fluorine-containing polymer (fluoropolymer), especially the quantitative determination of a metal impurity contained in a trace amount in a fluorine-containing polymer by using a so-called flameless atomic absorption spectrophotometer, and a process for the production of a fluorine-containing polymer with using said method.
DISCLOSURE OF THE INVENTION
Fluorine-containing polymers are used in various industrial fields, and it is very often that trace amounts of metals contained in the polymers as impurities such as iron, copper, nickel, sodium, potassium and so on cause problems. For example, in a semiconductor relating field, a fluorine-containing polymer such as a tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer (which is, hereinafter, referred to as "PFA") is used for a basket wherein a leak error may be caused in a P-N bonding when the trace amounts of the metals such as iron, copper, nickel and so on are dissolved out and they are present in a semiconductor device.
In addition, since an alkaline metal such as sodium, potassium and so on is likely to cause insufficient withstand voltage of an oxide film, it is important to know the amounts of the metals contained in the fluorine-containing polymer. Further, also during production of the fluorine-containing polymer, it is sometimes necessary to determine the trace amounts of the metals contained in the fluorine-containing polymer so as to ensure operation controls.
A method which has been hitherto used so as to quantitatively determine trace amounts of metals contained in a fluoroplastic comprises charging the fluoroplastic to be determined into a platinum made evaporating dish (of which platinum purity is usually 99.9%), incinerating the fluoroplastic with a burner or in an electrical furnace, and then dissolving a residue of the trace metals into a solution, which is subjected to the atomic absorption spectrophotometry so as to quantitatively determine the amount of the metals.
However, the above method has problems that it requires to use a large amount of the fluoroplastic and that its recoveries of metal elements are not so high. In addition, the platinum made evaporating dish is eroded by decomposition gases which are produced, when the incineration is carried out, which erosion causes a contamination problem by impurities contained in the evaporating dish. Alternatively, even though the evaporating dish is completely cleaned, there may occur a phenomenon that metals of the previous determination still remain on the dish (which is so-called "memory effect"). Therefore, these problems make it impossible to quantitatively and precisely determine the trace metals contained in the fluoroplastic.
On the basis of the above prior arts, trials have been carried out so as to make it possible to directly carry out quantitative determination of a trace amount of a transition metal contained in a fluoroplastic (see Pre-print of 33 rd Annual Meeting of Japanese Analytical Chemistry Association, 1 A 11, page 409 (1984)). This reference describes as follows: Even though direct quantitative determination of the trace amount of the metal contained in the fluoroplastic is carried out using a Zeeman graphite furnace atomic absorption spectrophotometer, detection of the metal is impossible since the metal contained in the polymer is volatilized out as a fluoride. However, such a trace metal can be stably detected when a metal sulfate thereof is produced under the coexistence of an inorganic additive such as KHSO.sub.4 during dry incineration.
In such a method, a temperature of about 1000.degree. C. is employed as a dry incineration temperature, and a detection limit of the metal is said to be about 20 ppb in the case of a sample amount of 10 mg. However, in this method, the addition of KHSO.sub.4 as an additional step is required, which provides another possibility of contamination, and further the detection limit of the me
REFERENCES:
patent: 4912528 (1990-03-01), Hwang et al.
Pre-print of 33rd Annual Meeting of Japanese Analytical Chemistry Association, 1 A 11, p. 409 (1984).
Daikin Industries Ltd.
Evans F. L.
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