ANALYTICA CHIMICA ACTA 125

DETERMINATION OF IRON IN WINE USING 2,4,6-TRIPYRIDYL- s-TRIAZINE

PETER COLLINS AND HARVEY DIEHL

Dcparrmenr of Chemistry, Iowa SIatc Unrversrty, A tries, Iowa (U S .4 )

(Received July r6th, 1959)

The first use of the now well known colorimctric reagent for iron, x,ro-phenan- throline, was for the determination of iron in wine (SAYWELL AND CUNNINGHAM~)

and its use has become more or less standard, the various procedures which have been proposed differmg primarily in the method used to dccomposc the sample prior to color development. Usually, the organic material present is destroyed by a wet ashing with nitric and perchloric acids or with hydrogen pero,xide. However, RANICK

AND SMITII~, utilizing the supersensitive iron reagent, bathophenanthroline, climinatc the usual wet ashing and extract the red tron(II) bathophenanthrolinc compound directly into isoamyl alcohol.

A new ferroine reagent, 2,4,6-tripyridyl-s-triazinc (TPTZ), has recently been in- troduced as an extremely sensitrve reagent for the colorimctric dctennination of iron2. This reagent posscsscs many of the advantages of bathophenanthrolinc and is much easier to prepare. TPTZ reacts with iron(I1) to give an intensely violet colored, water soluble ion, Fe(TPT2) 2 +a. In the presence of pcrchlorate, the iron(I1) derivative can be extracted into nitrobenzene. The molar extinction coefficients are 22,600 at 593 m/h in aqueous solution and 24,100 at 595 m/t in nitrobenzene. The permissible pH range is 3.4 to 5.8 in aqueous solution and when the extraction into nitrobcnzene is usecl, the PH range is increased to 2.7 to7.o.Thccolor conforms to Beer’s law in both solvents.

The object of the present work was to develop a suitable procedure for the dcter- mination of iron in wine using TPTZ and taking advantage of the extraction feature to eliminate the wet ashing step.

Reugcnls 2.4.6-Tripyrrdyl-s-triazine (TPTZ). 0 001 M Dissolve o 312 1~ of ‘I’l’TZ (synthesized by the

I’TlCthOd Of CASE AND I<OF+, available from the G Frcdcrick Smith Chemical Co., Columbus, Ohio) in a few drops of hydrochloric acid and dilute to I 1 with water.

Nydroxyla#tmoxrunr clrlortde. 10%. Dissolve IOO g of hytlroxylammonium chlorldc m goo ml of water To rcmovc iron add IO ml of o 001 M TPTZ and I g of sodium pcrchloratc and extract with 25 ml of nitrobcnzcnc.

Sodium acefatc-acetic acsd buf/er. Preparo a solution 2 M in acctm acid and 2 M in sodium acetate by dissolving IIS ml of acetic acid and 164 g of sodium acetate in water and diluting to I 1. To rcmovc iron, add IO ml of 10% hydroxylammonium chloride, IO ml of 0.001 M TPTZ, and I g of sodium pcrchlorate and extract the solution with 25 ml of nitrobcnzene.

Sodium psrcirCorafe. 10%. Dissolve IOO g of sodium pcrchlorate insgoo ml of water and remove iron in the same way as with the acetate buffer.

Standard zron solutton. Dissolve 0,250o (J of clcctrolytic .iron in 20 ml of hydrochloric acid and dilute to exactly I 1. Pipet 100.0 ml of this solution into a r-liter volumotric.flask, add IO ml

Anal. Cl&n. Aka, .22. (1960) x25-x27

126 P. COLLINS, II. DIEHL

of hydrochloric acid and dilute to volume wrth water. Dilute IOO o ml of thus solution and IO ml of hydrochloric acid to exactly I 1 to give a solution containing z 50 ,ug of iron per ml

Preparulzon of calibralion curve Pipct various volumes from 0 to 15 ml of a solution containing 2.50 pg of iron per ml into

rz5-ml scparatory funnels. Add z o ml of 10% hyclroxylammonium chlorlcle, 5 o ml of o oox M TM’%, 5 o ml of acctatc buffer and 1.0 ml of ~0% sodium pcrchloratc to each funnel. Extract each solution three times using 4 o-, z o- and 2 o-ml portions of nitrobcnzcnc Collect the extract\ of each solution in a xo-ml volumctrlc flask, dilute to volume with ethanol and dctcrmme the absorbancy at 595 rnp using f-cm cells

Proccdurc for detertnanulron of irou wrilr firchmmary wet czslrrng Prpct a 3 oo-ml aamplc of wmc into a zgo-ml conical flask f&ted with a reflux head Add IO ml of

nitric acid and 5 ml of pcrchloruz acid and heat to furncsof pcrchloricacid Cool the solution, add 20 ml of water and heat to boiling to remove any chlormc. After cooling the solution, add 2 o ml of 10% hydroxylammonium chloride, 2 omlof acctatc buffer anti 5 oml of o OOI M TPT% NcutrahLc the solution with ammotllum hydroxide to pi 4 to 5 using a plr mctcr or pu mchcatmg paper. Transfer the solutron to a x25-ml scparatory funnel, add 4.0 ml of nitrobenscnc and shake vigorously for I mm Allow the phases to scparatc and gently swirl to rcmovc drops of nitrobcnscnc clmgtng to tkc upper walls of the funnel. Rcpca t the cxtmction using two 2 o-ml portions of nitrobenzcnc Collect the extracts in a IO-ml volumetric flask, thlutc to volume with ethanol and measure the absorbnncy at 595 rn1.r using I-cm cells. Run a blank through the cntirc proccdurc and subtract its absorbancy from the absorbancy of each of the other solutions

Fvocedure /or llre davecl detevnrtnntzon of EYO~

To a 3 oo-ml sample of wmc contamccl m a roo-ml beaker add 2.0 ml of 10% hydroxylarn- monium chloride, 5 o ml of ethanol, 5 o ml of acctatc buffer and 5 o ml of o oar M TPTZ. Meat the solution to boiling for 5 mm, cool and transfer to a r25-ml separntory funnel. Wash the bcakcr with 20 ml of ethanol and I o ml of 10% sodium pcrchloratc and add the washings to the scparatory funnel Extract the solution thrco times using one 4 o-ml and two 2 o-ml portions of nrtrobcnzcne and collect the extracts m a ro-ml volumetric flask Dilute to volume with ethanol and clctorminc the absorbancy of the solution at 595 rnp using x-cm cells Run a blank through the cntirc proccduro and subtract its absorbancy from the absorbancy of the sample solution,

RESULTS AND I)ISCUSSION

The iron content of several wines was determined using TPTZ in both the direct extraction and wet ashing procedures and also by I,ro-phenanthroline following wet ashing. The wine samples were obtained through retail outlets and were of U.S. and European vintage. All determinations were carried out in at least triplicate. The results are shown in Table I.

It is apparent that the determination of iron in wine by the direct TPTZ method usually, but not always, gives values which are lower than those obtained by wet ashingprocedures. This is presumably due to the presence of a very stable iron com- pound which is not broken by TPTZ. If this is the case, it may well be that the “complexed iron” is inactive in forming a turbidity in wine and that the results obtainccl for “uncomplexed iron” by this direct method may be more useful to the wine producer than a knowledge of the total iron content. Various conditions, such as length of heating and ethanol concentration, were changed; but in no case was it possible to complctcly recover the iron from certain wines using the direct proce- dure. The iron which is not recovered remains in the aqueous phases as shown in one case by a wet ashing of the remaining water solution.

The iron content of the Medoc Bordeaux Red Wine was also determined by the direct method of BANICK AND SMITH and found to be 6.46 mg of iron per 1, almost identical with the direct TPTZ method.

The procedure employing preliminary wet ashing followed by determination of the

kf?ad. Chiffl. ,‘fCtU, 22 (x960) X25-127

DETERMINATION OF Fe IN WINE 127

iron with TPTZ does have &stinct advantages over the usual x,xo-phenanthroline methods. A smaller sample may conveniently be used clue to the increased sensitivity of the reagent and the extractability of the iron derivative into nitrobenzene. Iron may be easily removed from the reagents and the blank reduced to essentially zero. Also, it is unnecessary to remove the excess perchloric acid as is the case in the deter- minatlon employing r,ro-phenanthroline.

TABLE I DETERMINATION OF IRON IN WINE USING TPTZ

(Each result gtvcn IS the average of at least three detcrmmations)

Itahan SWISS Colony Cali- fornia Sherry Mel&s Oh10 State Tawny- Port Medoc Bor- deaux Red Wine Virgmla Daru White Wine Virgima Dart Red Wine Ambassador Cahforma Burgundy Richeliau Ca- lifornia Port Homestead Piestengel Rhubarb Wane

2 54

3 79

7.53

4 42

5 81

4 73

5*15

2 27 0 00 2.27 0 ox 2.28

o 07

0 I.5

! 0 10

0 01

0 o.?

o 07 4.69 0 ox 4 24

0.01 5 12 0 02 4 68

* 51

3.80 o 04

7.56 o 04 6.44

4-48 0 or 4 16

5.82 o 03 537 -

0 01

o 03

o 08

0.11

0.02

0.01

0.02

SUMMARY

Procedures arc dcscribcd for thu dctcrmrnation of iron m wine using 2,4,G-trrpyrldyl-s-trlazinc, a new fcrroine rcagcnt. One procedure mvolvrng wet ashmg with mtrlc and perchlorlc acids gives results comparable to those obtamcd usmg the usual r,xo-phcnanthrolrnc method while a direct cxtrnction proccdurc often gives ldw but rcproduciblc results indicating the prcsencc of “complcxccl u-on” m the sample.

Rl%UMti

Dcux mdthodcs sont d&r&es pour lc dosage du fer dans lc vin au moyon d’un nouveau rdnctlf, la 2,4,6-trlpyridyl-s-tri.kzine. On procEdc solt B une mmdrahsation par voic humldc soit par extraction daectc.

ZUSAMMENFASSUNG

Es wcrden zwci Mcthoden beschrlcben Lur Bcstimmung dcs Elsens m Wcm mit Hllfc von 2,4,6-Tripyridyl-s-trlazm nach vorausgchcnder nasscr Vcraschung odcr Extraktion

REFERENCES

1 L. G SAYWELL AND B. B. CUNNINGHAM,IPUL Eng.Chem., Anal. Ed.,g (x937) 67 * W. M. BANICK AND G. FREDERICK SMITH, An&. Chim. A+, 16 (x957) 464. 8 P. F COLLINS, H. DIEHL AND G. FREDERICK SMITEI, Anal. C&~rn.; 31 (1959) 1682. 4 F. H. CASE AND E. KOFT, J. Am. Ghem. Sot., 81 (-1959) go&-: