Abstract: A method for making an monoclonal antibody specific for vitamin B12 by immunizing mice with vitamin B12-b-acid and isolating hybridomas that produce monoclonal antibodies which have an affinity constant for B12 greater than 5.times.10.sup.9 l/mol is disclosed.

Abstract: For the determination of vitamin B12 a sample solution is incubated with at least two receptors R.sub.1 and R.sub.2 of which R.sub.1 mediates the binding to the solid phase and R.sub.2 is labelled, whereby a receptor is used as one of the receptors R.sub.1 or R.sub.2 which contains a monoclonal antibody capable of specific binding to B12 that has an affinity constant of at least 5.times.10.sup.9 l/mol and a receptor is used as the other receptor R.sub.1 or R.sub.2 which contains B12 or an analogue thereof, the two phases are separated and the label is measured in one of the two phases.

Abstract: A process for the dissolving off of an analyte bound to a binding protein by breakdown of the binding protein using a cleaving agent which cleaves --S--S-- groups into SH groups in the alkaline range, wherein a 1,2-dithiolan-3-carboxylic acid of the formula: ##STR1## is used as the --S--S-- group cleaving agent in which n is a whole number of from 1 to 8. The process is used for preparing samples for analytical or investigational processes for the determination of a liberated analyte and especially for immunoassays for vitamins such as vitamin B.sub.12, steroids such as testosterone or for thyroid hormones such as T.sub.3 /T.sub.4.