Patent ID: 7578953

Claim:
A method of sulfonating the surface of a resin-containing article, the method comprising: a) forming a first sulfonating gas composition, the sulfonating gas composition comprising a sulfur-containing gaseous compound provided from a gas source; b) contacting one or more first test samples with the first sulfonating gas composition; c) contacting the one or more first test samples with at least one neutralization composition; d) determining the amount of sulfur in the one or more first test samples by inductively coupled plasma analysis; e) measuring the amount of sulfur in the one or more first test samples by X-ray fluorescence; f) determining a calibration relationship between the amount of sulfur determined by inductively coupled plasma analysis and X-ray fluorescence wherein the amount of sulfur determined by inductively coupled plasma analysis is taken as an accurate value; g) forming a second sulfonating gas composition, the second sulfonating gas composition comprising a sulfur-containing gaseous compound provided from a gas source; h) contacting the article and one or more second test samples with the second sulfonating gas composition; i) contacting the article and the one or more second test samples with at least one neutralization composition; j) measuring the amount of sulfur in the first test sample by X-ray fluorescence using the calibration relationship determined in step f) to adjust the determined amount of sulfur; and k) adjusting concentration of sulfur-containing compound in the sulfonating gas composition or adjusting the time of sulfonating in subsequent sulfonation runs if the amount of sulfur determined in step j) is not equal to a predetermined value, wherein the first and second test sample each individually comprise a resin.