Spectrophotometric determination of tin in metals and alloys

404

SHORT

COMIMUNICATIONS

merely a standardization of the end-pomt byrcmovmg the variationof colorsensitivity and perception of the human eye from the procedure The color sensitivity from person to person 15 not 50 important at levels of MgO >o SO/~,but becomes increasmgly the important a$ the MgO approaches o IO”/“. Thus, although we demonstrated tcproducihlhty and precision of visual titration cncl-points for MgO from o.oz~/~ and above for high and low calcium and phosphate concentrations, standardization of end-point dctcctton at a constant wavclcn@h spcctrophotomctrically makes endpoint dctcction much easier and consistent. Conlane~italO~1Conafiany, Kesenrch ajrd 13cveZo~ment, Powa Ctly, Okla. (U S.A.)

(Rcccivcd

April

DONALD E JoRJ~AN D~NALU E. MONN

zzncl, 1967)

AUClLClbl,,l A&I, 39 (19G7)‘Ior--.)O.(

Spectrophotometric

determination

of tin in metals and alloys

From some recent workr*Q it appeared that the spectrophotometric MIBICphcnylfluorone method for the determination of tin in stcelacoulcl be greatly simplified by isolating the tin by solvent extraction as the iodide By using the extraction it is possible to dispense with the sulfide scparatlon, the double carbamatc extraction and the use of oxalate and peroxide as complcxmg agents rn the color development with phenylfluoronc. Moreover, bccausc of the high specificity of the iodide extraction, the method has proved to be applicable to the analysis of highly alloyed steels and to many of thr important nonferrous metals and alloys Analysis

of steel D~ssolvc the sample contammg I-IS pg of tin in 5 ml of hydrochloric acidmtnc acid mixture (4: I), adcl 2 ml of sulfuric acid and then destroy the nitric acid with a small excess of formic acida. Boil to a volume of 2 5-3 ml to expel most of the hydrochlorrc acid. Add about IO ml of a 42-ml portion of g N sulfuric acid1 and heat to boiling to clrssolve all salts. Cool ancl add the remainder of the g N sulfuric acid Add 5 ml of 5 M sodium iodicle solution and then add 7.8% sulfurous acid m small portions until most of the iodine has been reduced Swirl, allow to stand and add further o.zg-ml portions of sulfurous acid until the recluction is complete Transfer the solution to a 75-ml separatory funnel and shake for I mm with IO ml of benzene. Dram off and discard the lower layer as completely as possible (If a clean cut separation of the layers IS prevented because of bubbles which collect at the interface, stopper and sllalce vigorously for a few seconds In the above and all

Anal,

Chrrn

Acta,

39 (xgG7)

404-406

SHORT

COBIhlUXICATIONS

405

future extractions, wash the stopper free of non salts under the drstlllcd water tap each time it 1s removed from the funnel ) Wash down the msrdc of the mouth of the funnel with 5 ml of a freshly mixed portion of wash solutron (IO ml of 9 N H&04 f I ml of 5 M NaI solution) and shake for IO set Allow the layers to separate, turn the stopcock through 180~ 3 or 4 times to wash out non salts and dram off and discard the lower layer. Repeat the wash once more Fmally wtih rnsrdc and outsrde the funnel stem with water Add about o 5 ml of mtrrc acrd to the funnel, shake for IO see and dram completely to a xoo-ml beaker Close the stopcock, wash down the msrde of the funnel with about 4 ml of benzene, shalce a few seconds and dram to the beaker Place the beaker under an air Jet on a low tempcraturc hotplate in a hood and leave until all benzene and lodmc has been removed Add 4 drops of 70% pcrchlorrc acid and 4 drops of sulfuric acid and heat on a flirme to destroy traces of organic matter Fmally flame carefully to expel all acid Cool, add I o ml of I * 3 hydrochlorrc acid, swirl and ttlt the beaker to wet all precipitated salts on the wall of the bcakcr and then dctermme the trn by the spcctrophotometric MIRK-phenylfluorone methods, omitting the addrtron of ammonnun oxalate and hydrogen peroxide in the analysis and m the preparation of the calibratron graph.

Tests have shown that the iodrde extraction provrdcs an elegant separation of tm from large amounts of non or from xoo-pg quantities of the other IO metals which mtcrfcre m the spcctrophotomctric phenylfluorone method for tin3 The isolation may not be as complete when larger amounts of these other mterferrng metals are present Nevertheless, the separation IS good enough for most types of steel The only common steels that cannot be amalyzcd are those which contam apprccrable amounts of tungsten Tungstic oxide collects m the bcnzenc layer with the tm; perhaps it would be possible to filter off the oxide before the iodide extraction Typical data obtained 111the analysrs of vmous NBS sttccls are shown m Table I It I\ seen that TABLE ANALYSIS

I OP NBS

SAMPLES

Sronple

OF STEIIL

.‘V” l’1rt -_I_-_-Presetrf

-

Fottrrd --_

'165

0 004

0 004

3Ga (Kr-Inlo) 5xa (IC) I 23b (Cr-NcNb-Ta) I Goa (I gCr-I 4N1-3310) 170 (0 ZTI)

0 01 I 0 011

0 01 I, 0.012 00x1 0 011

0 013 0018

0 013 o 018

---

sample Iz3b which contams 0.75O/~of moblum, o ZOO/~of tantalum and o 18% of tungsten can be analyzed. In order to prove that the color obtained m the spectrophotometric analysis of this sample was due to tin and not to the 3 metals mentioned above, o 5 ml of standard tm solutron was added to the aqueous extract from the analysis of the sample and the extraction and analysis was repeated The recovery of the tm was quantttative. Aural

Clrrm

ffcfu,

39 (1907)

404-406

SHORT

406

COXINUNICATIONS

‘l’hc proposed method can also be used in the analysis of many of the common non-ferrrJu\ metals and alloys, The procedure used was as follows Dissolve the sample in nitric acid or in liydrochlorlc acid plus, If necessary, a few drops of hydrogen pcroxidc Add 13 ml of sulfuric aclcl and tlicn evaporate to wlute fumes to expel the vol,Wc acds. If mtrlc ncd 11;~sbeen used, add. a little water and take to fumes again AVOKI cxccsswc loss of the sulfuric acid Cool, add 37 ml of water, heat to bolhng to dissolve all salts, cool ancl add 5 ml of sochum todldc solutmn If more than a small amount of iodme is produced, reduce It with 9ulfurous acd nncl then procefzd to the hcn/,cnc extra&on In the analysis of dummum, chromium or their alloys dissolve the sample m hydrochloric ;LCI~ (or in acl~ rcgla followed by treatment with formic ;LCL~)ant1 then talc0 only to inclplcnt fumes of sulfuric ad to avolcl precipitation of .duniinum or chromium sulfate. In order to dctermlne whuA~ metals can be analyzed by the above method, 0 5-g portions of tin-fret metal or the cqulvalcnt amount of metal salt plus, 111all CZLW\,o 5 ml of stanclrrrcl tin solution were analy~ccl. Quantltatlve recovery of the tm ~a.5 obtalnccl m the analysis of Nl, Co, Mn, Cd, In, %n, Al and Mg. For a variety of ic,~~oii5, tlic metals Cc, Sb, SC, Tc, Pb, Cu, UI, ‘1’1,U, and ‘I% could not be analyzed hlol cover, difficulty woulcl l~roI>ably be cncountcl ccl in the analysis of iLltOyS containor more of these mctdls The extraction of x00-pg ing alqm2clablc amounts of once portions of tltamum(IV), bismuth and copper is ml m the roclrclc cxtractron, but wllcn present III large amounts, apprcclable quantrtlcs of thcsc metals accompany the tin m the extraction The copper :lppciLrs to bc collectccl 111the bcnzcnc layer as precipitated copper(1) mclide rather than ab extracted copper(1) m&de It 15 of interest to note, however, that NBS zinc base alloy g4b winch contains IO/, of copper ancl o 005% of tin 1ia.sbeen successfully analyzccl

(1
Apnl

5t11, rgC,7)