(19)

(11)

EP 0 663 998 A1

(12)

(43) Date of publication: 26.07.1995 Bulletin 1995/30 (21) Application number: 93922522.0 (22) Date of filing: 04.10.1993

(51) International Patent Classification (IPC):  G01N 33/ 22( . ) G01N 33/ 28( . ) G01N 21/ 35( . ) (86) International application number: PCT/EP1993/002735 (87) International publication number: WO 1994/008226 (14.04.1994 Gazette 1994/09)

(84) Designated Contracting States: AT BE CH DE DK ES FR GB GR IE IT LI LU NL PT SE (30) Priority: 05.10.1992 EP 19920309075 28.01.1993 EP 19930200229 (71) Applicant: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V. NL-2596 HR Den Haag (NL)	(72) Inventors: BOYD, Andrew Pool Lane Ince Cheshire CH1 3SH (GB) TOLCHARD, John, Michael Pool Lane Ince Cheshire CH1 3SH (GB)