(19)

(11)

EP 0 419 486 A1

(12)

(43) Date of publication: 03.04.1991 Bulletin 1991/14 (21) Application number: 89902527.0 (22) Date of filing: 13.02.1989

(51) International Patent Classification (IPC):  G01N 21/ 03( . ) G01N 21/ 64( . ) (86) International application number: PCT/GB1989/000142 (87) International publication number: WO 1989/007757 (24.08.1989 Gazette 1989/20)

(84) Designated Contracting States: AT BE CH DE FR GB IT LI LU NL SE (30) Priority: 12.02.1988 GB 19880003334 (71) Applicant: NATIONAL RESEARCH DEVELOPMENT CORPORATION London SE1 6BU (GB)	(72) Inventor: SNOOK, Martin Middelsex HA5 5BT (GB) (74) Representative: Chandler, Derek Richard  Patents Department British Technology Group Ltd 101 Newington Causeway London SE1 6BU London SE1 6BU (GB)