1221
V O L U M E 2 1 , NO. 1 0 , O C T O B E R 1 9 4 9
part of thv Confusion iritimtiuC~dinto the literature in rcwnt y~'ai.s
tc~mincdfrom the use of filter-type colorimrtrrs for this restud!-. Rtbgarding the detr~rminationof creatinine using picric acid, it has been repeatedly found (10, 11) that sw('rt' dc%viations f r o m t h r Brer-1,anibert (quation occur and, furthermore', that t w o supposedly standardiztd instruments of the sanit. manufacturc~ may differ considcrably fi.om one another (11). Thus I,ainh(~i,t found that, in ordvr to stay within the relatively short rangtl of linearity using tho Ilvvlyn instrunient, it was necessary t o dilutv urint samples, first t o a constant specific gravity, and thr:n again (about 1 to 20). B y using the, more precise Beckman instrunwnt the range of linearity is so extended that a single dilution sufiws for over 90% of all urines tested. Furthwmorr, it has Iwc.n possible to study the convcrsion of creatine to creatinine, as wrll as the details of thta color reaction itsplf, with much grcatcsr prt.ckiori. This study, as rcported above, has confirnied thc original statc~mcntsof Folin ( 6 , 7 ) regarding the usefulness of thv .Jaff(. reaction and has dt>fined the analytical conditions in tht. mor(' I)rc&cb tclrnis possibk with modern instruments.
*CREATININE 100rnicmgrams
\CKYOWLEDGIIEYT
Tht, authote ~ 1 4 t1o acknoii lcdyr the technical assistancta of Jacobstm and ICleanor c'lai k during the early stages of tht. work. Dt.tt,rminations ot carbon, hldiogen, and nitrogen \\('I ( * donr. IIV thti Clat h llicroanalytical I.ahoratorv, Urhana, Ill. \Vtmcii
'400
440
Figure 6 .
480
520
560
600 640
3pectral thsorption Curves LITERATURE CITED
Thrl aut how' i'sptt i i i i h , i i t s N Y I ' ( ~ dt'siyii(d priniarily to discovcxrth(8 optinium p H at whichquantitative conversion of creatine to crcxatininv occurred. Independrnt of the type of buffer, this optimum point was found to lie nt'ar pH 2, a finding which could not h a w 1 ) c ~ i predicted i froni tht! work of Icdgar. I n thv light of this infor( I ) proccdurcl has dccrcmcd, ratht>r than ty of t h c b original Folin method, as has b t ~ > n pointed out by Lambert ( I O ) . However, contrary to thc statc~tiient of 1,ambcrt. the effrrt is due, riot t o the presencca of picric acid p c ~ but to the hydrogen ion concentration of picric acid solutions. \Vith tht. advent 01' nioclcrn photoelwtric colori~neters and Fpc'ctrophotoineterb, it is natural and appropriate> that the J a f f ~ i ' c ~ t cion t roctudird i n mot'(' prc.rist1 terms. Curiousl>- c~liouyh. ~
1
,
1 x 8
( I 1 Aibanese, -1..I., and Wangeriii, D. SI.,Science, 100, 68 (1944). ( 2 ) Benedict, S. 11.. J . B i d . Chem., 82, 1 ( 1 9 2 9 ) . ( 3 ) Clark, \T. &I., "Determination of Hydrogen Ions." Baltimore, Williams and n'ilkins Co.. 1 9 2 2 . (1) Edgar. G., arid Shivel,, H. E.. J . A m . C h r m . Soc.. 47, 1 1 i O (1926).
(5) Edgar. G.. and Wakefield, I t . A , , Ibid., 45, 2242 (1923). (6) Foliu. 0..J . Bioi. C'hem., 17, 4 6 9 ( 1 9 1 4 ) . ( i ) Folin, 0.. arid Doiry. 12. A , , I b i d . , 28, 3 4 9 ( 1 9 1 i ) . ( 8 ) Hunter, .I.,"Ci.eatine and Creatinine," New York. I2oiigiiritir~, Green and C o . , 1 9 2 8 . (9) Jaffe. &I.. 2. ~ h u s i o l C'hrm.. . 10. 391 ( 1 8 8 6 ) . (10i Lambert: G . ' F , J . Riol. Chem., 161, 678 ( 1 9 4 5 ) . (11) Peters, J. H., Itlid., 146, 179 ( 1 9 4 2 ) . (12) Iteynolds. E. L.. n t ~ dC'Iai,k. I>.C . , Chi'idDrJwiop.. 18, I55 i i ) I i r R E C E I V E lDl a r c h 9,1940
Separation of Calcium from Magnesium by Oxalate Method A Critical Study 'roKE
t LOL T H 1
Cfreniicul Znstitrcte, Oslo Zniuersitj., Oslo.
T
1115 osalate mrrhod for deterniin:ition of Calcium an(\ its sopnr:~tionfrom niagnesium dates from the earliest times of (?I. Fresenius (4)in 1868 st:ited that thtl prwipitato of enlciuni oxalate is always contaminated 1))- magnfxsium oxalate. It is tlic'refore neeessay?. t o dissolve the precipitittr in hydrochloric arid, and reprecipit:ite calcium oxalate with :iinmoni:i. Richard? a n d co1l:il)or:itol~s ( 1 6 ) in 1901 a h o ~ v c dthat iiiidei, certain conditioiis :L single precipitation oi' c:ilc4uni i, 1 I'w,iant s d d r e r b , 5-orweginn Defense Kcv?ari,li E ~ t a h l i s h m e n t ,Cli \ i - i o n Kieller pr. 1.ilIe.troiu S o r w a y .
\oric.ir\
sufhcieiit. In thr, niethotl tlesCritwl, :I large :mount oi :minioniurn chloi,ide i h :idtl(d. Cnlcium oxalate is precipitated 11y drop\\-ise addition ot' :immonia to a calcium chloride solution cont:tining oxalic. avid find hydrochloric acid. After t h r precipitation an us(*essof :ammonium oxalate is added. Fischer ( 3 ) in 1926 pul)lished a paper, disparaging the work of 1iich:ircts. He shon.ec1 th:it magnesium oxalate is not precipitated f r o m supers:ttui,:itecl solutiolis when special precautions are taken. I n the determinatioii of c.nlciuni, Fischcr usod but ii slight o \ c r s s of ammonium os:il:it
