according to this invention , an improved immunochemical method is provided for detecting hypoxic tissue and cells in tumors and other living matter . a feature of the present invention is based on the discovery that the above - described compounds of the present invention , such as 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole , metabolically bind preferentially to hypoxic tissue rather than to normal oxygenated tissue . furthermore , it has been discovered that the s enantiomer of 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole is 5 - 10 times better as a competitive inhibitor of monoclonal antibody binding to solid phase antigen than is the racemic mixture . the special properties of the s enantiomer of 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole and its derivatives make them a preferred embodiment of the invention . the enantiomers may be synthesized , for example , by reacting 2 - nitroimidazole with r or s epichlorohydrin in the presence of a catalytic amount of potassium carbonate to form the corresponding r or s chlorohydrin derivative of 2 - nitroimidazole . refluxing the chlorohydrin derivatives dissolved in absolute ethanol containing an excess of piperidine , produces the desired products as the free base r &# 39 ;= piperidinyl !. acidification with hydrogen chloride gas followed by evaporation of the solvent provides the hydrochloride salts of the chiral free bases . an alternative route to the r and s enantiomers of 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole include the stereoselective reduction of 1 -( 2 - keto - 3 - piperidinopropyl )- 2 - nitroimidazole with chiral reducing agents . enantiomers of the other compounds of formula i may be synthesized in an analogous manner . as previously noted , the administration of the selected 2 - nitroimidazoles to animals or humans results in the metabolic binding of the nitroaromatic compounds to hypoxic tissue in tumors . the specific binding is thought to be due to the presence of enzymes which interact with the chiral 2 - nitroimidazoles on a three dimensional basis . the enantiomers of a racemic drug often differ in pharmacodynamic and pharmacokinetic properties as a result of stereoselective interaction with chiral macromolecules ariens et al ., eur . j . clin . pharmacol ., 26 , 663 ( 1984 ); drayer , et al ., clin . pharmacol . ther ., 40 , 125 ( 1986 )!. the desired pharmacological effect is often associated with only one of the enantiomers in a racemic mixture . for instance , (+)- ketamine is the predominately responsible for an hypnotic effect whereas the (-)- isomer is the main source of side effects white , et al ., anesthesiology , 52 , 231 ( 1980 )!. 2 - nitroimidazoles have been studied extensively as hypoxic cell radiosensitizers . its clinical applications however , are limited by the development of central and peripheral neuropathies . the compounds of present invention bearing a basic piperidinyl or piperazinyl group as hydrochloride salts significantly improve water solubility and tumor uptake . although the main object of this invention is on the method of detection hypoxia in tumors , we recognize that these compounds may also be used as cytotoxic agents for treating hypoxic tumor cells . the administration of the chiral 2 - nitroimidazoles to a tumor - bearing patient results in the nitroreductase activity leading to binding of the drug to the hypoxic tissue . a biopsy sample of the patient &# 39 ; s tumor is taken for purposes of investigation by use of the antibodies developed by raleigh et al , u . s . pat . no . 5 , 086 , 068 , which describes the general methodology for the inventive method , and is incorporated by reference herein . for example , at a predetermined time prior to analysis of a tumor , e . g ., 20 hours prior to surgical inspection of the tumor by , e . g ., biopsy , the tumor bearing animal or patient is administered the hypoxic cell marker by injection . an administration dosage to provide a whole body concentration of 5 - 150 micromolar is preferred . the tumor sample taken is then analyzed according to the invention . the chiral 2 - nitroimidazole compounds administered to the patient are the same compound which are used as haptens in producing antibody reagents . as a general overview of the process , the biopsy sample of the tumor may be fixed in cold ethanol at 0 °- 20 ° c . for histological examination including light microscopy , fluorescence microscopy or electron microscopy . alternatively or in addition , a sample of the fresh tissue can be weighed , homogenized and analyzed by enzyme linked immunosorbent assay elisa , raleigh , et al ., br . j . cancer , 69 : 66 - 71 ( 1994 )!. finally , a fresh biopsy sample can be enzymatically digested and made into a single cell suspension for analysis by flow cytometry . in each case , specific antibodies which recognize the nitroimidazole compounds bound to the hypoxic cells are used as the primary analytical reagents . in each case the analysis is conducted according to standard techniques of immunohistology , elisa or flow cytometry . in each case , and as suitable , standard immunochemical detection schemes incorporating commercially available secondary immunochemical reagents can be used including but not limited to fluorescence - labeled , enzyme - labeled and ferritin - labeled or gold labeled secondary antibodies . standard image and flow cytometric analyses are performed on the tumor samples to estimate the extent of tumor hypoxia in the tumor samples and to relate this to therapy outcome and / or the presence of other physiological factors which might affect therapy outcome . other features of the invention will become apparent in the course of the following descriptions of exemplary embodiments which are given for illustration of the invention only and are not intended to be limiting thereof . the entire disclosure of all applications , patents and publications , cited above are hereby incorporated by reference . without further elaboration , it is believed that one skilled in the art can , using the preceding description , utilize the present invention to its fullest extent . the preferred specific embodiments are , therefore , to be construed as merely illustrative , and not limitative of the disclosure in any way whatsoever . the file of this patent contains at least one drawing executed in color . copies of this patent with color drawing ( s ) will be provided by the patent and trademark office upon request and payment of the necessary fee . fig1 shows the immunostaining of the tissue section of a c3h mammary adenocarcinoma labelled in vivo with racemic 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole ( magnification × 400 ). immunostaining is observed in cells distant to tumor vasculature arrow ! as expected of hypoxic tumor cells . sections such as these can be used to quantify the extent of tumor hypoxia in terms of the ratio of labelled cells to total cells in the sections . to 1 . 15 gram of 2 - nitroimidazole in 20 ml of absolute ethanol was added 100 mg of potassium carbonate and 1 . 0 gram ( r )- epichlorohydrin . the reaction mixture was refluxed overnight . the cooled reaction mixture is added to 150 ml of saturated aqueous sodium chloride containing 5 % sodium bicarbonate . the reaction mixture was extracted with ethyl acetate ( 3 × 10 ml ) and the organic extract was dried over anhydrous sodium sulfate , filtered and concentrated to give 1 . 87 gram of the r enantiomer of 1 -( 2 - hydroxy - 3 - chloropropyl )- 2 - nitroimidazole . a similar reaction procedure starting with ( s )- epichlorohydrin gives 1 . 45 gram of the s enantiomer . the chiral intermediate was reacted with a four fold excess of freshly distilled piperidine in 25 ml of refluxing absolute ethanol for 16 hours . the reaction mixture was evaporated to dryness , the solid residue was taken up in 25 ml water , and acidified with 2n hcl . the solution was washed with dichloromethane ( 3 × 15 ml ). the aqueous layer was basified with 2n sodium hydroxide solution and extracted with dichloromethane ( 3 × 15 ml ). the organic extract was dried over anhydrous sodium sulfate , filtered and concentrated to give a pale yellow solid of the r or s enantiomers of 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole . the hydrochloride salts of the respective r and s enantiomers were prepared by means of dissolving the free bases in ethanol and treating with a slight excess of alcoholic hydrogen chloride . in elisa studies according to literature procedure raleigh , et al ., br . j . cancer ., 69 : 66 - 71 ( 1994 )!, it was shown that the s enantiomer of 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole was 5 to 10 times better as a competitive inhibitor of monoclonal antibody binding to solid phase antigens than was the racemic mixture . for these studies , the solid phase antigen for coating the elisa plates consisted of racemic 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole reductively bound to thiolated ficoll by the radiation chemical technique used to bind the same compound to bsa . example 3 -- oxygen dependence of 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole binding to mammalian cells in tissue culture . for the determination of the oxygen dependence of binding of 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole to hypoxic cells , emt6 cells suspended at 10 -- 6 cells / ml in 25 ml of phosphate buffered saline ( pbs ) were placed in a series of silanized 125 ml gas collection tubes which were thoroughly washed with distilled water and autoclaved before use . the cell suspensions were equilibrated with gas phases containing varying amounts of oxygen by means of repeated gas exchanges under partial vacuum . the cells were maintained in suspension by constant agitation of the tubes on a shaker . a small volume of solution in pbs was injected into the cell suspensions to achieve a final concentration of 100 micromolar of the hypoxia marker , 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole . the cells were incubated for 2 hours at 37 ° c . after which time the cells were harvested , washed extensively and analyzed by elisa for covalently bound hypoxia marker . the elisa values for binding of 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole under different gas phase oxygen concentrations were reported relative to the maximum degree of binding achieved under anoxic conditions (& lt ; 10 ppm o 2 ). the oxygen dependence of 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole binding to emt6 cells in vitro showed half maximal inhibition of binding at a gas phase oxygen concentration of 0 . 1 % which was comparable to published values of 0 . 1 to 0 . 3 % for half maximal inhibition of misonidazole binding in this cell line . antibodies to 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole reductively bound to proteins were used to reveal hypoxic cells in mouse c3h mammary adenocarcinomas by standard peroxidase immunostaining techniques ( fig1 ). for these experiments , c3h carcinoma cells in single cell suspension were injected into the gastrocnemius muscle of five week old male c3h mice at 10 5 to 10 7 cells per mouse . tumors were investigated when they reached a diameter of 8 mm . 1 -( 2 - hydroxy - 3 - piperidinopropyl )- 2 - nitroimidazole was administered intraperitoneally at a concentration of 60 mg / kg mouse weight . mice were killed after 4 hours by cervical dislocation and the tumors excised and fixed in 10 % neutral buffered formalin for 24 hours . the fixed tissue was then embedded in paraffin and sectioned at 4 - 6 microns onto apts - coated capillary action slides . the sections were deparaffinized and immunostained by a biotin - streptavidin - peroxidase indirect immunostaining procedure . by counting the number of labeled cells and the total number of tumor cells in many representative fields of the tissue sections such as shown in fig1 it was possible to estimate the fraction of hypoxic cells in a particular tumor cline , et al ., int . j . radiat . oncol . biol . phys ., 28 : 921 - 933 ( 1994 )!. although this example illustrates results with experimental mouse tumors similar procedures will be used on biopsies taken from human patients . although preferred embodiments of the invention are described herein in detail , it will be understood by those skilled in the art that variations may be made hereto without departing from the spirit of the invention or the scope of the appended claims .