A new application of atomic absorption spectrophotometry: determination of phthalic acid by solvent extraction with neocuproine-copper(I) chelate

ANALYTICA

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CHIMICA

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SHORT

ACTA

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COMMUNICATIONS

A new application of atomic absorption spectrophotometry: determination of phthalic acid by solvent extraction with neocuproine-copper(l) chelate In atomic absorption spectrophotometry, a hollow-cathode lamp which emits the spectral lines belonging to the element being determined is generally used as a light source. 13ecausc of this restriction, it has been impossible to determine organic compounds and most non-metals by atomic absorption methods. In the course of studies on solvent extraction with metal chelate cations’, it was found that cuproinc (z,c)-dimethyl-r,xo-phenanthroline) dissolved in chloroform was a sclcctivc extractant for phthalic acid in aqueous solutions containing a moderate amount of copper(I), and that it was possible to determine a small amount of the organic acid by measuring the ahsorbnncc of the extracts spcctrophotomctrically. ‘To apply thcsc phcnomcna in atomic absorption spcctrophotometry, chloroform was unsuitable because of incomplete combustion in the flame and the toxicity of the decomposed products such as phosgene. To find a suitable solvent for atomic abuorption spcctrophotomctry, various ketones, alcohols and esters were tested for the extractions; methyl isobutyl ketone containing ncocuproinc proved to be a selective

Wavelength Fig. with

(rnp)

I. Absorption spcctm:(~) 2 - IO-~&[ phthalic acid

extracts (rcfcrcncc:

by

IV1 I3K without

phthnlic

acid;

(2)

cxtrncts

by MIBII;

Ml13K).

cstractant for plitlialic acid in the samcc way as chloroform containing cuproinc. An indirect method for the dctcrmination of nitrate, based upon the same principle, has recently been reported”. This paper is .conccrned with the determination of phthalic acid by atomic absorption. Figure I showy the visible absorption spectra in the organic phase. It may

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be observed that the presence of phthalic acid in aqueous solution leads to a considerable increase in the extraction. The absorbance maximum of the extracted species is at 456 rnp. The chemical formula of the extracted species is ‘asslimed to be {[Cu(neocuproine)z] - [GH.I(CO&]}. It therefore appeared possible to determine the phthalic acid as well as nitrate by spraying the extracted MIRK solution into the flame of an atomic absorption spcctrophotometer with a copper hollow-cathode lamp. To establish the optimum conditions for the determination of phthalic acid, various factors wverc studied: the effect of the concentrations of copper(H) ions (as copper sulfate) and hydroxylamine sulfate, the PH of the solution, the presence of the diverse ions, and also the effect of instrument settings such as fuel pressure and burner height on the intensity. Recommended $7ocedure fo7 the calibration curve The atomic absorption measurements of the organic phase were made with a Hitachi atomic absorption spectrophotometer (Model x39-0420). Mix I ml of coppcr(I1) sulfate solution (I - IO-~ M), z ml of 5% hydroxylaminc sulfate solution, 5 ml of 0.25 M phosphate buffer solution, and varying amounts of standard phthalic acid solution (I * x0-4 M, 2-10 ml). Dilute the solution with water to 25 ml, and shake for 2 min with 10.0 ml of a MIBK solution containing: neocuproinc (2 10-3 M). Measure the absorption using a copper hollow-cathode lamp as light flame with an air flow-rate source at the 3247 A copper line. Use an air -acetylene of about 7.0 l/min and an acetylene flow-rate of about 1.1 l/min. Under the above conditions, the calibration curve w
Labovatovy of A~ralytical Paczclty of Scieme, Hi~oshinta Univevsity, Hiroslkzra (Jaflan)

T. KUMAMARU Y. HAYASHI N. OKAMOTO E. TAO Y. YAMAMOTO

Chemistry,

I Y. Y,ul,tMoro,

N. OKAMOTO AND IL TAO, Japczrl Analyst.

2

15.

‘r.

I
(Received

January

TAO, N.

~KAnloro

AND

Y.

YAMAMOTO.

14 (1965) 343. Cko~r.sot.Jupuw, 38 (1965)2204.

&ill.

24th. x966) .dnal.Chi?S.rida. 35 (rg6G) 524-525