The present invention includes a method for analyzing reactions. The method includes the steps of providing a solution of at least one acceptor chemical and at least one donor chemical. The donor chemical is capable of donating a chemical moiety to the acceptor chemical. The solution further includes at least one controller chemical that affects the reaction between the donor chemical and the acceptor chemical. The solution is then incubated so that a portion of the acceptor chemical reacts with the donor chemical to form an acceptor product. Unreacted donor chemical is separated from the acceptor product. The acceptor product or the donor chemical is then measured using X-ray fluorescence. Another aspect of the present invention includes a method for analyzing protein function. The method includes the steps of providing a solution of at least one acceptor chemical and at least one donor chemical. The donor chemical is capable of donating a chemical moiety to the acceptor chemical. The donor chemical includes a functional group selected from ester, anhydride, imide, acyl halide, and amide. The solution is then incubated so that a portion of the acceptor chemical reacts with the donor chemical to form an acceptor product. Unreacted donor chemical is separated from the acceptor product. The acceptor product or the donor chemical is then measured using X-ray fluorescence. Yet another aspect of the present invention includes a method for analyzing protein function. The method includes the steps of providing a solution of at least one acceptor chemical and at least one donor chemical. The solution is then incubated so that a portion of the acceptor chemical reacts with the donor chemical to form an acceptor product. Unreacted donor chemical is separated from the acceptor product. The acceptor product or the donor chemical is then measured using X-ray fluorescence. An additional analytical method is also used to measure either the acceptor product or the donor chemical.