Determinacion Colorimetrica de Magnesio

8/9/2019 Determinacion Colorimetrica de Magnesio

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VOL. 2 (1948) ANALYTICA CtiIMICA ACTA 241'

COLORIMETRIC DETERMINATION OF MAGNESIUM

I-I. A. J. PIETERS, XV. J. HANSSEN, AND J. J. CEURTSCmltrd I_abornlor_v of the Nelhcr lands SIafe Coal M a n es, G c f een ( N e l l r c r l a m f s )

INTRODUCTION

When magnesium hydroxide is precipitated in a solution containing titan yellow,the precipitate is coloured by adsorption of the dye. When the solution containsa protecting colloid the magnesium hydroxide remains in the colloidal state,retaining the ability of adsorption of the dye.

Under the proper conditions the intensity of the orange colour of the solutionis a measure of the magnesium content.

.

GINSBERGI uses a I %‘s starch solution in dilutedglycerol as the protecting colloid,an excess of titan yellow and light of 546 rnp from a mercury lamp. SINIGAGLIA~does not use an excess of titan yellow. LUDWIG AND JOHNSON~ use starch and lightOf 523 In/.&.

The procedures described in the literature I-g differ only in the compositionand the quantity of the reagents. As they are developed for the determinationof Mg in water, they practically do not contain data on interfering substances.

In an attempt to develop a satisfactory procedure to determine Mg-+” in waterand in silicates we studied the influence of the following factors usbIg a Lcifophotometer.

I. Wave-length of the light2. Stability of the solutions a3. Quantities of the reagents4. Extinction as a function of the concentrations of magnesium and of titan

yellow5. Influence of Ca, Fe, Al, NH,c and other electrolytes.The results are presented in graphs and tables. We devised a procedure which

enables us to determine quantities up to 2 mg of Mg with an accuracy of 0.02 mg.The procedure is relatively simple and saves us a lot of time. The accuracy isgreater than that of the gravimetric method.

Iron and aluminium interfere, Ca and alkali-chlorides don’t. The method wasadapted to the analyses of water and of silicates.Re eren ces . 253.

16


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242 H. A. J. PIETERS, W. J, HANSSEN,

RESULTS

I. The wave-length which gives optimal resultsWe used this light in our dctcrminations.

J. J. GEURTS VOL. 2 (1948)

proved to be 534 p (Fig. I).

FIN. x. Absorption spectrum of solul~ons wth and wthout IQ

2. A solution of starch in water does not give satisfactory stabilityBetter results arc obtained with a starch solution containing glycerollo.

0 5oooI

60 120 I80t mmn_lFig. 2. The cxtlnctlon cocIliclcnt as a function of the tlmc, after adding different

01 I ‘;& st,lrch solution, wh~lc the Rig-content IS kept constant.

(Fig. 2).

quantities


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VOL. 2 (1948) COLORIMETRIC DETERMINATION OF MAGNESIUM 143

Fig. 3 summarizes the results obtained with solutions containing starch andglycerol in varying proportions.

Gelatine and gummi arabicum are unsuitable as protecting colloids (Fig. 4).We recommend a mixture of IO ml 2 ‘s starch solution and IO ml glycerol whichgives reproducible results after 40 minutes. The colour does not fade during 3 hours(Fig. 3). Small variations of the quantities of starch and glycerol arc of no im-portance.

3. The quantity of sodium hydroxide added to the solution influences the resultsand conscqucntly has to be kept constant (Table I). \Vc recommend 10.0 ml 2.0 Nsodium hydroxide.

ThBLIZ I

INPLUICNCE 01’ SMALL \‘ARIATIONS IN TII C QUANTITIES Or TllC \OLUl-IONS

Optlmi1I ahorptwn at wave-length 534 mp wlicn C;L+~ > x0 mg

TABLE II

REQUIRED QUANTITICS Ol- TITAN YRLLOXV

x m RI :I mg titan yellow

0.0 2.40.G 3.6

12 .I.8r.8 G.o

I

4. Fig. 5 gives the extinction as a function of the concentration of titan yellow(Big bcmg kept constant).Rcfevemxs p. 253.


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H. A. J . PIETERS, W. J . HANSSEN, J. J. GEURTS VOL. 2 1948)_-

Fig. 3. The cxtmctlo~ cocficicnt as a functionof the time, nftcr ncld~ng chffcrcnt qunntlticsof a mixture of stdrcti und glycerol when the

Mg-content is kept constant

iI.0

a75

0.5

025

0.0 I c

Fig. 5. The cxtinctlon cocfficicnt as n function of Fig. 6. The extmction coefficient as a functionitlc titan yellow conccntriltlon when tllc qunntlty of the Mg-conccntratlon when the quantity

of Rig IS lccpt constant tltnn yellow is lccpt constant

5I.400

1000

OIYOO

Fig. 4. The cxtinctlon cocfficicnt as a function ofthe tlmc when dlffcrcnt qu.mtltics of gum arabic

;Lrc ~lclcd11 = solutions contnmlng the same quantity of MgB = bt;lnkGum arnblc solution: IO g/l

IOOOOI I I

15 30 4.3-*mgk


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Fig.6 gives the extinction as a function of the Mg content (titan yellow constant).As long as the titan yellow is in excess, the extinction is a linear function of the

Mg content.The required quantities of titan yellow arc expressed by the equation a > 2 x+ 2.4 (Table II).

Calcium deepens the colour of the solution. WC found that with IO mg Caf” thisinfluence reaches a maximum value (Table III). In solutions containing IO mg Ca+athe required quantity of titan yellow is:

I

TABLE ILL

INPLUENCIS OF CALCIUX

0.326 0.6450.336 0 780

IO 0.348 0 82815 0.35 I 0.83220 0 350 0.830

I I

The lnflucncc of Cil+a rcnchcs A maxI-mum

Fq. 7.Saturation vnlucs in the prcscncc of Ca -mg M9

Z5 - Mognrs iu m hydro xide

s o f u r o t e d

MOpQsiUm h y d r o x r d eu n s o t u r o t s d

a > 3 x + 3.5 (Fig. 7)IO mg titan yellow is sufficient for quantities up to 2 mg Mg.

APPLICATIONS

I. Determi nati ozzs of M g+2 in w ater .

Different quantities of a dilute solution containing s = o - 2 mg Mg+2, pipettedinto IOO ml flasks, were mixed with

5 ml calcium chloride 2 mg Ca+” per ml)IO ml glycerol10 ml starch solution (20 g/l)x0.0 ml titan yellow (I g/l)10.0 ml sodium hydroxide (2.0 n)

and filled to the mark with distilled water. After I hour the extinction wasdetermined.Refer ences p . 253.


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246 I-I. A. J. PIE’I-ERS, W. J. HANSSEN, J. J. GEURTS VOL. 2 (1948)

Table IV and Fig. S show us that the extinction coefficient (E) is a linear functionof the Mg-‘2 content (x) :

= 0.500 - x + 0.347E - 0.347x -=

0.500 -

TAI3LE IVEXTINCTION CODFFICIF.N~ ~5 A I-UNCTION OF

l1lL3 QUANTI ry 01’ nl Aci r I sl unr

0 000 0 010

0.934

I ZOG

_x =E - 0.34 7

0.500

F16.8. The cxtlnctton cocffhcnt. as il functronof the qunntlty of hIf~ +~ n pure soliillons 720 I80

w 47

(II), Fe (III), POj3 and SiO,.the maximum quantities which

WC then determined the influence of -41, FeFrom Tables V, VI, VII and VIII, we set thatdo not interfere arc:

0.05 mg Al0.05 mg Ye5 “7g PO,0.5 mg SiO,

per IOO ml of the dilute solution, containing x = o - 2 mg Mg.

SiO, and scsquioxidcs are eliminated in the well-known way. In the filtratefrom the iron- and aluminium hydrosides the Mg+2 is determined colorimctrically,This filtrate contains relatively large amounts of alkali- and ammonium chlorides.From Table IS and S we conclude, that sodium chloride diminishes the extinctionand increases the time of dcvclopmcnt of the colour to 2 hours. The NaCl alsoRcfcmces p. 2.53.


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VOL. 2 x948) COLORIMETRIC DETERMINATION OF MAGNESIUM 247

TABLE VINFLUENCE OF ALUMINIUM

Present mgIbIg+ 1 Al+3

0.3000 05 0.500 0.2Q60.1 O.4 73 0 3.12o.G o-297

, I I 0.05 mg A1+3 per x00 ml intcrfcrc

TABLE VIIINI ’LUENCE Ol- PtIOSI’iIATES

Prcscnt mg --BIb’+10P0,-3

mg rag+?found

0 0 o-3.37 0.00

0 0.880 r.ng

I 0 .8 ; 3 ’ 072 o 88G 1.10

I .oz) 3 o 89-1 1.1 I4 0.8Q.1 I II

5 0.83 I 1.1 II---II

< 5 mE: pod3 per 100 ml leas no influcncc

TABLE IXINFLUENCE Or SODIUM CHLORIDE

I 400 mg NaCl per x00 ml mtcrfcrc

References p. 953.

TABLE VIINI-LUENCE OF FC (XI) AND PC (III )

0.05 0.5040.300 0.1 o.skQQ

0.2 0.4 750.5 O.*i,IO

0.298

0.2880.240

0.170I I I I

0.05 o.G53 o.59Go Goo 0.1 o&+0 0.570

0.2 OX,32 0 55405 0.615 0.520

5 0.05 mg Fc

1_.___--1-00 ml lnlcrfcrcer

TABLE \‘I11INI -I.UENCC OI- DISSOLVED so,

0 o.G78 0.6080.5 o GG5 0.582

0 Go8 00 0.5541.5 0.5082.0 0.48G

---> 0 5 mg SIO, per 100 ml lntcrfcrc

TABLE XINI’LUENCX OF SODIUX CHLORIDE. TIIL TIME

Ol- RCACTION IS VARILD FROM I t.0 3 HOURS

Prcscnt mg

RrgfaI I I

60 0.79080 0 790

I .03 100 0.776120 0.782140 0.779IGO o.77G180 o.77G

I I INaCl glvcs a constant vnluc from 2 to 3 hoursafter the ncldltlon of titan yellow and sodrum-hyclroxldc


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248 H. A. J, PIETERS, W. J. HANSSEN, J. J. GEURTS VOL. 2 x948)

influences the proportion x (Mg+z): a (titan yellow). With x < 1.8 mg of Mg+ain the presence of I g NaCl we have to add 15 mg titan yellow. For this reason

the maximum quantity of Mg+2which can be determined is 1.8 mg. Fortunately

the quantity of NaCl in the filtrate is always the same, as the quantity of sodiumhydroxide which is used to fuse the silicates is practically constant (We alwaysuse 8 grams of NaOH per gram of the sample). Ammonium chloride interfereswhen more than 2 mg is present. Therefore we have to eliminate it by evaporatingthe filtrate and driving off the ammonium chloride by heating the residue.

TARLE XI

TIIE EXTINCTION COEPFICIENT Ab A FUNCTIONOF THE QUANTITY OP nlhCNE5IUnI IN THEPRESENCE OF soDIunr CI-ILORIDE AND 15 rng

INSTEAD OIr IO mg TITAN YELLOW

Prcscllt rng

1

RI&a&

rng ~TK:+~

NaCI found

0 0.3250.300 0.510 0.310o.Goo 0.680 o*5gg

1000 0.900 0.850 0.886I .200 I .032 I.192I .500 1.212 l..w61.800 I .qoz 1.81~

WhCn X = m& Of hfg+l

x=E- 0.325

o.Goo

Fig. g. The cxtinclion cocfficicnt ;LS R functionof the quantity of Mg+a In the prcscncc of

I &ram of sotlinm chloriclc

We determined the extinction coefficient of solutions containing 0-1.8 mg ofMg+2 and I g of NaCl (Table XI, Fig. g) and found that:

E = 0.600 - x + 0.325

& - 0.325x = 0.600

We checked the method with synthetic silicatesmuch time (Table XIII) and is more accurate(Table XIV).

Rcfermces p. 253.

(Table X;I). The method savesthan the gravimetric method


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VOL. 2 1948) COLORIMETRIC DETERMINATION OF MAGNESTUM 249

TABLE XIIDETERMINATION OF MAGNESIUB IN SYNTHETIC SILICATES

Composition of the silicates in o~ by weight

SiO, 50.0 Fc202 8 MgO 0.0-3.0A’202 31.0 cao 4 SO4 rest

Y0 nrgo

prcscnt -

0.000.50I .oo

1.502.002.503.00

hlonk (InclucllngL g N l)

o-378 0.00.544 0.60.700 1.10.81 I x.50.954 2.01.123 261.207 2.9

o-333

found

The error IS nboutlg%

TABLE XIII

A. in waterTIME REQUIRED FOR THE DETERIIINATION

.TIME IN HOURS

hrcthod I Gravimctrlc I Photometric

Preparation : Eliminationof SiO,, Al, Fc and Cn

Total Workingduration hours

Dctcrminntlon Dctermmatlon

Total Worklng Total Workmgduration hours duration hours

15 3 24 2 2 114

B. In slllcntcs (starting wltll the filtrate of the sesquloxidcs) including the time rcquircdto drlvc off the NH,-salts.

TIME IN IIOURS8

Gravlmctrlc Photometric

Total Working Total Workingduration hours duration hours

32I

3I

4I

314

Refer ences p. 253.


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250 Il. A. J. PIETERS, W. J. HANSSEN, J. J. GEURTS VOL. 2 1948)

TAI3LE XIV

CO?dPARISON OP TlIR RESULTS OF TZIE DETERhlINATION 01’ RI6 IN SILICATES l3Y THE CRAVIMETRIC

sxnlrm DI~ECIPITATION AND *I-J~E x~1IoTonlrxxIc n7rmIoD

Prcwnt

0.00

0.501.001.502.00

2.503.00

FOUtlCl

gcnv~mctr~cdllyJ

error* fotomctr~cxlly error

Io 15-0 15 (blank) -I_ 0.15 0.00.85-0.3 -I- C-J 0.61.4-1.5 -I- 0.45 I cI .85-l .9 -I- 0 4 1.52 3 -1.3 -b 0.3 202.7 -2. i f 0.25 2.63.2 -3.2 _1- 0 2 2.9

+ 2’:+ 0.10.0

+ :::

- 0.1

’ Not corrcctccl for tllc bhnk.

RECOMMENDED PROCEDURE

I. Primiplca. Delevmi?taL ion o/ M gk2 in waler

When sodium hydroxide is added to a solution of Mg+2 which contains a suitableprotecting colloid and titan yellow in excess the magnesium hydroxide combinedwith the dye gives a relatively rather deep coloured colloidal solution, the ex-tinction coefficient of which is a linear function of the Mg content. The influenceof Ca+” is eliminated by adding Ca+2 in excess,

2. Reagents

a. Calcium chloride, 2 mg Ca-‘-” per ml

b. Glycerol (C. P.)c. Starch, 20 g/ld. Titan yellow, I g/le. Sodium hydroxide, 2 N

3. Samfile

Start with V = maximal 50 ml of the sample, containing not more than 2 mgof Mg+2.

4. Pvocen?wc

Transfer V ml of the sample to a IOO ml measuring flask and dilute to 50 ml.Add successively

5 mlx0 mlI0 ml10.0 ml10.0 ml

calcium chlorideglycerolstarch solutiontitan yellow solution andsodium hydroside.

12cfcrc?tccs p. 253.


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VOL. 2 1945) COLORIMETRIC DETERhIINhTION OF BIAGNESIUfiI 251

Mix after each addition.Fill to the mark with distlllcd water and mis. Determine the cstinction coeffi-

cient after I hour at different depths of layer.5. Result

Calculate the quantity of RIg+z (s mg) present in 1’ ml of the sample:

E---E*x = _-_oo-5

whcrl L = tllc cstinction cocllicwnt of the solutionE, = the cstinctioI1 cocficicnt of a blank

6. Rmnnrka The solutions of starch and titan yellow must be preparccl dailyb) 50 ml ol the sample must not contain more than

0.05 mg Fe0.05 mg Al5.0 mg PO,0.5 mg SiO,,

300 mg electrolytes

I . PrincipZc

An aliquoi portion of the filtrate from the hydroxides of Fe and Al, from whichthe ammonium salts have been elimmatcd, is treated with titan yellow and sodium

hydroxide. after the addition of a suitable protecting colloid. The c.xtinctioncocfficicnt of the red solution is a linear function of the quantity of Mg. Theinfluence of the reagents is determined by a blank.

2. Sample

a. Silicates which can bc decomposed quantitatively by hydrochloric acid.Eliminate the SiO,, dilute the filtrate in a measuring flask to 250 ml, and takeIOO ml from which the iron and aluminium are eliminated as the hydroxides bydouble precipitation. Collect the filtrates and fill up to 250 ml. Take a portion ofthis filtrate, containing not more than 1.8 mg Mg, evaporate in a porcelain diskand eliminate the ammonium salts by heating. Prolong the heating for 1.5 hours

’ at 550” C. Take up the residue in water and transfer to a IOO ml measuring flask.

Proceed as described in the procedure for water.b. Silicates which have to be fused with sodium hydroxide or alkalicarbonates.I g of the sample is fused in a nickel crucible with S g of NaOH or in a platinum

cruclblc with II g of N&O,. The SiO, is eliminated in the well-known way. Thefiltrate from the SiO, is transferred to a measuring flask and diluted to 250 ml.


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252 H. A. J. PIDTERS, W. J. HANSSEN, J. J. CEURTS VOL. 2 (1948)

In 200 ml of this filtrate the iron and aluminium are eliminated by double preci-pitation. The filtrate from the hydroxides is made up to 250 ml. Proceed with

V ml of this solution (set Table II).

y0 nigo cxpdd p-7 ldd mg NnCl

0-8) 50 -

4-B 25 5008-12 15 750

Evaporate the V ml of the solution in a porcelain disk, drive off the ammoniumsalts and heat 1.5 hours at 550 o C. Dissolve the residue in water and transfer toa IOO ml measuring flask and dilute to 50 ml.

3. Reagentsa Calcium chloride, 2 mg CaC2 per mlb. Glycerol (C.P.)c. Starch solution, 20 g/ld. Titan yellow solution, 1.5 g/le Sodium hydroxide, 2.00 nf. Sodium chloride, IOO g/l

4. Procedure

Add to the solution in the measuring flask successively:5 ml calcium chloride

I O ml glycerolIO ml starch solution10.0 ml titan yellow10.0 ml sodium hydroxide

Mix after each addition. Pill up to the mark and mix Determine the extinctioncoefficient at different depths of layer.

5. Resaclls

Calculate the quantity of MgO (x mg) present in V ml of filtrate:

E - (E, + p) - 1 658x=

0.600& = extinction coefficient of the solutionE, = extinction coefficient of the blank containing IO ml sodium chloride solution

P = difference between a blank, starting with the reagents usedSiO, and the sesquioxides, and the E,

6. Remarks

to eliminate the

The solutions of starch and of titan have to be prepared daily.Rcfcr crr ccs p. 253.


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SUMnIARY

From a critnxl study of the colorimctrrc tlctcrmmatron of magnesium with titan yellow

WC concluded that:a. titan yellow must bc present in cxccss;b. a mixture of glycerol and starch solutron is satisfactory as protecting collo~d;c. the influence of calcrum bccomcs constant with conccntratlons IO mg Ca+? per IOO ml:d. aluminium, iron, phosphate, ammonium and srhca mtcrfcrc;e. alkali-ions interfck when prcscnt in large quantltlcs.The method IS rapid and the accuracy is sntlsfactory and can bc rccommcndcd for the

dctcrmmation of bfg+” in water and In silicates.

On n 6tud16 la d6tcrmmatron photomctrlquc du magn6slum ct dkrtt Its condltlons quldonncnt dcs rkultats satisfaisants. Cc sont. ~diinc dc trtnnc cn cxces, melnngc cl’nmitlon ct dcglyckrol pour stalxliscr l’hydroxydc du mngnksmm, prbcncc d’unc qunntit6 convcnablc dccalcmm (l’mflucncc du Ca +s attcint uric valcur maximum ct constantc).

L’alummlum, lc fer, lc phosphate ct l’ammonium nc pcuvcnt Ctre pr6sent.s quc dans dctr&s falblcs conccntratlons.Lcs ions Na+l ct K+s nc donncnt dcs difhcult6s qu’A dcs concentrations 61~~6~s. La m6thodc

a bt& apphqu6c a l’annlysc dcs caux et dcs slhcntcs. Ellc cut rnpulc ct plus cxnctc quc la methodcgravimbtriquc.

ZUSAMMENFASSUNC

Die photomctrischc Mngncslumbcstimmung wurdc studlcrt uncl die Bcdmgungcn bc-schricbk, die hefrrcdigcnd~ Rcsultatc crgcbcn. Dlcsc sind :

Ubcrschuss Titaneclb. Gcmisch von Amidon und Glvzcrol. urn tlas hIa~ncsiumhyclroxydzu stabilisicren, An&schhcrt cmcr passcndcn Mcngc K&urn-(dcr Elnfluss ion Cn+3-crrcichtcm konstantcs Maximum).

Alumimum, Eiscn, Phosphat und Ammonia durfcn nur in schr schwachcr Konzcntrationvorhanden sein.

Na+ und K+ vcrursachcn nur Schwrcrigkcitcn bci stdrlccrcn Konzcntrntioncn. Die Mcthodcwurdc zur Wasscr- und Sihlcatanalysc angcwnndt. Sic 1st schncll und gcnaucr als dlc gravi-mctrrschc Bcstimmung.

REFERENCES

1 H. G;INSB RG, 2. EZcklr och.. 45 rg3g) 829.9 I;. SINIGAGLIA, Di e Ckewzc. 55 (1942) 36.).3 E. C . LUDWIG, C. E. JOHNSON, Imi. Eng. C/r ., Rnnl. Ed., r .+ rgqz) 895.4 Lab. dcr Atlas Wcrkc A.G., Di e Chemte, 55 1934) 218.6 C. URMHC. R. BARIL, Mtltrochemxe, 14 (1934) 343.e 13. LANGE, KoCorrmelrtscire AnaZyse, gG (1941).7 I;. D. SNELL, C. T. SNELL, Coloranrefric naethods of analysas, 47G (19.15).s E. 13. SANDELL. Coloramelric dcfermrnaf~ons of l~accs of wzfaLs. 305 rg+.{).0 Sfamiard me lhods fov fhs exa ma ~~afzon of wa fer n tld sc wa gre Igq G) p. Gr .

10ZULKOWSKY, Die Clrerrr ie, 53 1942) 218.

Received February zoth, Ig48

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Determinacion Colorimetrica de Magnesio