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An abso lute me th od wa s deve lope d for th e de te rmin a ti on of boric ac id by coulome tri c titrim etry. Th e prec is ion of th e me thod , ex pressed as th e s ta nd a rd de viation of a s in gle de te rmin ation is 0.0033 pe rcen t. C ha nges in th e inves ti gate d titration param ete rs produ ced no s ignifi cant effects on th e titrati o n res ult s. Indi c a ti ons are th a t within th e un ce rtainty of meas ure me nt s the me thod is b ias free.Key words: Acc ura te a na lys is; bori c a cid : co ulometri c titra ti on ; hi gh-p recision acid im e try; hi gh prec is io n co ul ome try. . IntroductionTh e National Bureau of Standard s condu cts a great deal of researc h towards es tabli s hm e nt of absolute standard s in all areas of th e meas ure me nt field . One ar ea whi ch e nables analyti cal quantifi cation of c he mical property on the absolute basis is co ulo me try. For thi s reason, ove r a numbe r of years, an inte nse effort has bee n mad e to d evelop me thods for precise analysis and to test the acc uracy of th ese methods [1 -5].1 This paper is one of a series of articles on th e de velopm e nt of pre cise coulometri c me th ods and th eir appli cation to c harac te rizati on of high purity standard refere nce materials (SRMs).Th e expanding use of boron and its co mpounds in nuclear tec hnology a nd th e NBS program co ncern ed with the iss uan ce of an SRM for ne utron flux monitorin g necessitated th e de ve lopme nt of a me thod for th e prec ise a nd acc ura te determination of thi s ele me nt. Th e mos t wid ely used me thod for the determination of milligram amounts of boron involves titration of boric acid in the presence of a polyol [6], us ually mannitol. Howe ver, thi s method is somewhat empirical in nature , partic ularly with re s pect to the amount of polyol required for titration and moreo ver, is generally precise to only a fe w parts p e r th ousand. Le Duigou and Lauer recently re ported a procedure for the coulome tric de te rmination of boron [7]. Th eir precision for l50-mg samples of boric acid was on th e orde r of 0.02 pe rce nt. Thus, th e m ethod appeared promising from the standpoint of precision, but th e di s turbin g fact is that these authors found a di screpancy of 0.1 perce nt be twee n the co ul ome tri c valu e a nd the va lue obtain ed b y conventional acidim e tri c titration . Referrin g to the coulo-* Presc nl ~Iddr~ss: \I c th ods Hesear('h a nd Tec hni(' a l Service Divi s ion. Eastrna n Kodak. Hoc hesle r, New Yo rk 14603. IFi gures in brackets indi cat e lit erature re fe rences at th e e nd of t hi s paper. me tri c me th od , th ese a uthors co ncluded that further studi es are necessary to improve its acc uracy. This co nclusion alone was s ufficie nt to a rouse our inte rest in the co ulometri c be havior of th e sys tem, particularly from th e s tandpoint of poss ible so urces of e rror whi c h apparently have not bee n ruled out in th e coulometric inves ti gation s of Le Duigo u and Lauer.W e th erefore und ertook inves ti gati on ...