DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, a method of preparing samples of human serum or plasma for assay for carcinoembryonic antigen (CEA), is described which is rapid, convenient, and less expensive than methods used heretofore.
The method of the present invention comprises diluting the sample with a buffer solution to a slightly acid pH, mixing the sample with hydrophilic silica at room temperature, allowing the mixture to stand for a short period of time, and separating the silica from the sample.
Within the scope of the present invention is an improved assay for CEA incorporating the herein disclosed preparative methodology.
The hydrophilic silica employed in the methodology of the present invention is characterized by having a large specific surface area and a relatively small average primary particle size.
The specific surface area of the silica useful in the methodology of the present invention is from about 100 to about 400 m.
sup.
2 /g, and preferably from about 130 to about 380 m.
sup.
2 /g.
The surface area of the silica is determined according to the method of Brunauer, et al.
, J.
A.
C.
S.
60, 309 (1958).
The average primary particle size of the silica used in the practice of this invention is from about 7-16 nanometer (millimicron).
The amount of silica employed in the practice of the invention varies from 10 mg to 100 mg and preferably 35 mg to 80 mg.
The preparatory method of the present invention comprises diluting a sample of from about 0.
2 to about 0.
5 ml of plasma or serum.
The dilution of the test sample with an acidic buffer is necessary to maximize the sensitivity of the assay.
The sample, thus diluted, will have a slightly acidic pH, i.
e.
, a pH from about 6.
0 to about 6.
5 and preferably 6.
3.
Examples of buffers which can be used in the present invention include conventional acidic buffers, such as, for example, an ammonium acetate buffer, sodium acetate, sodium citrate, and the like, would be suitable.
A sufficient amount of the buffer is utilized to assure that the pH of the sample is slightly acidic, i
|
LCD 
