Interference study of alkali metals on aluminium determinations by atomic absorption spectrophotometry

Intcrfcrence study spcctrophotomctry

of alkali

metals

on aluminium

determinations

by atomic

absorption

Atomic absorption spectrophotomctry is an cxccllcnt method for the dctcrmination of aluminium in diffcrcnt samples. However, a nitrous oxide-acetylcnc flame is ncccssary, and the high tempcraturc causes some ionization of the produced aluminium atoms, so that the absorption of the characteristic radiation is decreased. A sample solution containing alkali metals readily produces alkali metal ions in nitrous oxide-acctylcnc flames. This cffcct causes a certain degree of intcrferencc in the aluminium determination dcpcnding upon the amount of alkali metal prcscnt’.‘. In thiscommunication, the intcrfcrcnccs from alkali metals (sodium, potassium, ccsium) on aluminium dctcrminations arc rcportcd and the effect of cesium on the determination of aluminium in rocks containing high amounts of alkali metals is dcscribcd. Appuratus

and reclgents

All mcasurcmcnts wcrc made with a Pcrkin-Elmer model 303 atomic absorption spcctrophotomctcr with readout and rccordcr. The standard solutions wcrc made from high-purity aluminium metal (99.99 ‘x, Al), and the alkali metal solutions from pro analysi sodium chloride, potassium chloride and ccsium chloride (Merck, Darmstadt). Procedures

Two scrics of solutions containing aluminium (50 p.p.m. Al and 100 p.p.m. Al) with increasing amounts of sodium, potassium and ccsium wcrc prcparcd. The two most sensitive rcsonancc lines for aluminium, 309.3 and 396.2 nm, wcrc used for analysis. Rock sumplc (200 mg) with a high content ofsodiurn (I+‘!-<, Na,O) and potassium (9:i;: K20) was dccomposcd with hydrofluoric acid in polycarbonatc Erlcnmcycr flasks (Nalgcne Company) as dcscribcd previously”, and diluted to 100 ml ; 25 ml of this solution ilnd 10 ml of cesium reagent solution (10 mg Cs per ml) wcrc diluted to 100 ml. The corresponding standard solutions contained the same ccsium conccntration. Absorbanccs wcrc measured at 309.3 nm in the nitrous oxide-acctylcnc flame. Discussion

Figure 1 shows the intcrfcrencc of increasing amounts of alkali metals on the aluminium absorption for 50 p.p.m. aluminium at 309.3 nm. Similar cffccts were found with 100 p.p.m. aluminium and at 396.2 nm. To avoid this ionization intcrfercncc, it is ncccssary to add a high concentration of an alkali metal to both standard and sample solutions. According to the values for ionization potentials, cesium (3.87 eV) is the most suitable alkali metal to USC, and it is easily ionized in high-tcmpcraturc flames. Although potassium can bc added to the sample and standard solutions, sodium and potassium cannot then bc dctermincd in the same solutions. The ionization interfercncc ofalkali metals on each other can also beeliminatcd by adding the same amount of ccsium solution to sample and standard solutions, thus Anul. Chiw.

Acta.

54 (1971)

I64-iGS

SHORT

165

COMMUNICATIONS

. 0

.

0.100 50 loo Fig. I. Intcrfcrcncc (C, Al + Nu.

L 500 ---...-Alkali mctol (p p m ) of alkali metals on dunlinium.

LL1

1000

Al concentration:

50 p.p.m.

Al. (0)

cesium another advantage over potassium addition. Five parallcl analysts of a rock sample gave a mean value with a standard deviation of 0.12 and a relative deviation of 0.5 same sample by addition ofexcess of EDTA and back-titration with xylcnol orange as indicator, gave the value 24.34(x, A1,03. which is with the atomic-absorption results.

Al + c’s, ( x ) Al + K.

giving

(Received

26th

November

of 24.23 ‘x, AI,O_, ‘x,. Analysis of the zinc solution with in good agrccmcnt

1970) rlmrl.

<‘/liftI.

ACfil.

54 (1971)

164

I65