VOL. 19 (1958) COLORIMIETRIG DETERMIXATION OF Fe(CN),-3 437

and, when 2 lo-mm Ncsslcr test-tubes arc used. up to dilutions of I : s-100 (D = I o-e-7). The qualitn- tivc lnvcatigation glvcs good results even when ionS of the fwst group of the uwai analytical procc- durc for anions arc prcscnt; the scnsitivlty is 1 . I s*loS (0-i IO-0.7).

REIXRENCES 1 F. ~USCAR6SS ASD E. ~,ORIESTlE, .4nnlcs rcftl sot. cspaii. fis. y g~tittt. (~Ifndrtd). 4413 (1948) 319. 2 1:. I~USCAR~NS AND J. ~\HTIGAS, AII~. Clrinr. .Ictn. IG (1957) 452. 3 Tables of Rcagenfs /or I~~ovgnn~c .4nnCysis, 3rd report, International Commlttccnn New Analytical

Reactions and Rcagcnts of the “Union Intcrnationalc tic Chimic”, lstm, l’arw, x948. I 4 I. &I. KOLTIIOFF, Phnrm. Il~ceklhd, 59 (rgzr) 6G

Rccclvcd March 2.+th, 1958

As stated recently by 13A1'13R1, glyoxal bis[z-hydrosy-anil 1, which is a Schiff base (I), forms colourcd inner complex salts with copper, cobalt, nickel, cadmium, mangancsc and uranyl ions, with the general formula (11).

(1) (11)

The respective salts were isolated as &hydrates by warming a mcthanolic solution of the corresponding UXtiltCS with a methanolic solution of (1).

It seemed interesting to invcstigatc a possible application of the formation of the above-mcntioncd compounds and of those that could bc formed with other metals. It was found that under certain conditions the Schiff base is a highly sclcctivc rcagcnt for calcium ions. When its alcoholic solution is addccl to an aqueous solution of a calcium salt, followed by sodium hydroxide, a red precipitate is obtained. Barium and strontium salts show a similar behaviour, but curiously enough it was found that in the case of these two metals the colourcd precipitates once formed are destroyed by addition of alkaline carbonate, whcrcas the calcium compound remains unaltcrcd.

Aqueous solutions of the following ions were trcatcd with the rcagcnt plus sodium hydroxide and carbonate: aluminum, antimony, barium, beryllium, bismuth, cad mium, ccric, cesium, chromic, cobalt, copper, ferric, gold, lanthanum, lcad, lithium, magnesium, mangancsc, mercurous, mercuric, nickel, palladium, platinum, potassium, silver, stannous, stannic, thallium, thorium, titanium, uranyl, zinc, and zirconium. Disregarding the hydroxide prccipitatcs, of the above-mentioned ions only cobalt and nickel give a red precipitate, cadmium a violet one, and copper a dark coloured enc.

When the suspension of the calcium-glyoxal bis[z-hydroxy-anil] compound is

References p. 439

438 D. GOLDSTEIS, C. STARK-MAVER VOL. 19 (1958)

shaken with chloroform, the organic layer acquires a red colour. The copper, nickel and cobalt compounds do not hehavc like this, but the cad&urn compound, when similarly treated gives a blue coloured chloroform layer. It seems that the coloured chloroform solution is really an organo-sol. An indication for this assumption is the fact that the dry coloured prccipitatc when treated with chloroform does not dissolve.

From the above it can be concluded that the reagent is fairly selective for calcium. Specificity can be attained by using a sodium hydroxide solution containing cyanide, thus preventing (masking) the cadmium reaction through the formation of Cd(CN),-2 ions; in contrast, the calcium reaction is not affected by cyanide. It is convenient to follow the same proccdurc in the presence of large amounts of nickel, copper, and cobalt ions, which are likcwisc masked by the formation of complex cyanides. In this way the action of the reagent (which othexwisc would also bc consumed by these ions) is rcstrictcd to the calcium ions.

Although the composition of the calcium compound with glyoxal bis[z-hydroxy- anil] has not yet been investigated, it is probable that an inner complex salt with the general formula (II) is involved.

EXPERIMENTAL

I. Safuvnlcd sohficm of glyoxal bts[a-hydroxy-unil] in ellryl alcohol. This solution is stable for at least two months, even though it may darken a httlc.

The rcagcnt may bc l~rcl~ared according to UA~~K 1, by dissolving 4.4 g of freshly sublimed o-ami- IlcJphCnOl in I 1 wotcr at 80~ and adding 3.0 g of a 46% solution of glyoxal in water. Tlic mixture IR kept for 30 min at 80~ and afterwards for IZ 11 in the rcfrigcrator. The prccipltatc 1s filtered. washed with water and rccrystallizcd from methanol.

2. ro”A, solufio,l o/ sodium Itydroxlde. 3. ZO’Z/~ solulion of sodrum carlo,rale. 4. IO g pofasst?r,n cyahdc urtd IO g sodltrm lrydroxtdc t>l zoo m1 wuler. 5. Chloroform.

Prncedure

A drop of the neutral or acid test solution is treated succcssivcly in a micro test tube with 4 drops of the organic rcagcnt (I), I drop of sodium hydroxiclc, I drop of sodium carbonate and cxtractcd wtth 3-4 drops of chloroform. Aclclition of a few drops of water hastens the separation of the two laycra. A red COhJUr in the chloroform layer indicates the prcsencc of calcium. When testing for small amounts of calcium, a blank test is advlsablc.

Linlit of idenfifzalron 0.05 y calcium.

L.inrri of dtltrlion 1:1,000,000.

With the above proccdurc it is pc~ss~l~le to idcntlfy the following amounts of Ca:

Calcclon

20 Pt3

25 cCf3 30 c16 20 Pl3 ‘0 ccg o-5 M3

IN Lhe firtsorcc O/ CdXWt~

2000 pg strontium I M3 2000 pg barium 0.5 Pg f 000 pg magnesium

500 pg lead 5 PB 0.5 Pg

500 c(g iron 0.5 Pf!? 500 pg aluminum

--

In Ike pmcncb of

_soo pg fluoride 500 pg oxalatc 500 fig phosphate 500 pg sulfate 500 ,ug chromate

In the prcsencc of cadmium, copper, nickel, and cobalt salts, the procedure 1s the same as dcs- cribed above, but the alknlization should bc performed with a sodium hydroxide solution containing cyanide (reagent 4).

Referenrces p. 439

VOL. 19 (1958) SPECIFIC TEST FOR CALCIUM 439

In this way it is possible to idcntlfy:

I Pt3 0.5 PR I Pg I ccg

IOOO pg cadmium 5oo Irg copper 500 ,ug mckcl 500 pg cobalt

Dishtction between calcizrm oxide and the oxides of barilcm, strontium and magttcsium

It is possible to distinguish calcium oxide from barium, strontium and magnesium oxides without dissolving any of them. It is sufficient to treat the sample with the reagent solution. Only calcium oxide becomes red.

P~occdure. A little of the Iinelv powdcrcd solid IS trcatcd on a spot plate with one drop of the rcagcnt solution. hftcr cvaporat:on of the greater part of the solvent (by simply blowing through a pipcttc), the prcvrousIy white sohd ~111 bc tinted red rf calcium oxide is prcscnt.

The procedure can also be applied to a carbonate mtxturc, after previous lgnltmn of the sample.

Idehf icathr of calcium in ~ltarmacc~rlical products

I?EICL AXD SILVA~ described a test for detecting calcium in pharmaceutical prcpara- tions using sodium rhodizonate and sodium hydroxide as reagents. Calcium lacto- phosphate fails to give a positive response to this test. With the first proccdurc dcs- cribcd, the calcium present in this compound can be detected; a positive reaction is also shown by calcium pantothenate, “zalima” (containing I (yO calcium formate), calcium lactate, calcium gluconate and calcium laevulinate.

Prelir+nary experiments showed that glyoxal bis[z-hydroxy-anilJ may be a suitable indicator for the titration of calcium with EDTA. Further studies along this lint are being made.

ACKNOWLEDGItMENTS

The authors are greatly indebted to Prof. Dr. FRITZ FEIGL for his valuable suggestions and constant interest in their work.

They also thank the Conselho Nac:onal de Pcsquisas for fmanclal support.

SUAMMARY

It was found that glyoxal bis[z-hydroxy-anil] is a sensitive reagent for calcium. When the reaction is carried out as a spot test, as little as o 05 /cgCacanbedetcctcd. If appropriate conditions are maintained, the calcium test is specific The test dcscrikd is specially swtcd to detect calcium oxide in a mocturc of other colourless oxides, as well as to detect calcium in pharmaceutical prcpa- rations.

REFERENCES

1 E. BAYER, Ber., go (x957) 2325. a F. FEIGL AND E. SILVA, Drug Sla,rdnvds, 23 (1955) I x4. Set also l?. FEIGL, S$~of ‘resls zn Or@wic

Analysrs, 5th cd., Elscvicr Publ. Co., Amsterdam. 1.956, p. 509.

Reccivcd March 24th. rg58