at the same site or different sites at regular or irregular intervals thereafter with bleedings being taken to assess antibody titer until it is determined that optimal titer has been reached the host animal is bled to yield a suitable volume of specific antiserum where desirable purification steps may be taken to remove undesired material such as nonspecific antibodies before the antiserum is considered suitable for use in performing actual assays the antibodies can also be obtained by somatic cell hydridization techniques such antibodies being commonly referred to as monoclonal antibodies reviews of such monoclonal antibody techniques are found in lymphocyte hybridomas ed melchers et al springer verlag new york 1978 nature 266 495 1977 and science 208 692 1980 a wide variety of synthetic routes are available to one skilled in the art for derivatizing theophylline at its 9 position and coupling the derivative to the carrier following are descriptions of some such synthetic routes 2 6 dioxopurines can exist in two isomeric forms which are known by the trivial names xanthines 3 7 dihydro 1h purine 2 6 dione 1 and iso xanthines 3 9 dihydro 1h pyrine 2 6 dione 2 and are numbered as shown in formula 1 str5 according to this trivial nomenclature the 9 substituted theophylline derivatives and conjugates of the present invention are in fact.