1 - PHENYL - 3 - METHYL - 4 - TRIFLUOROACETYL - PYRAZOLONE - 5 AS AN EXTRACTION AND SPECTROPHOTOMETRIC REAGENT FOR Fe (111)

Abstracb A rapid, simple and sensitive extraction method for the determination of iron (111) spectrophotometrically in buffer solutions using 1-phenyl-3-methyl-4-ti-fluoroacetyl-pyrazolone-5 (HPMTFP) is described. The properties of the eolour 01 the extracted complex species with respect to pH of aqueous media, presence of synergists, various solvents time and diverse ions arc reported. Up to 500 p m of .Ag' K', ~ a * , I3a2', J3e2', Ca2'. cd2', ~o", M&'. Mn2*. hJi2*. pb2', yP' and zn2' do not interfere. The toleredce level of the following ions which interfere were determined (ppm) : cu2' 5 20, Ck4' S 8, C#'S 100. Mo6*s 8, If+ S50, P*s 300 , V" S 20 and w6' S 8. Beer's law is valid up to 10 ppm iron (111) (&, 7.32 * 0.08 X lo3 1 mol.' cm-' ) within an optimum pH range of 15 - 45.


INTRODUCTION
Acyl-pyrazolones have long been known for their versaitile application in the solvent extraction of metals14 from acid solutions. However, there have been very few studies of these promising chelating agents in other aspects of practical application. Apart from the spectrophotometric determination of Fe (111)' and v ( v )~~ using the 4-benzoyl derivative, other 4-acyl derivatives have not been studied in this direction. During our solvent extraction studies the trifluoroacetyl derivatives of pyrazolone-5 (HPMTFP) was observed to be much more sensitive in both the cflraction ,md spectrophotometric determination of Fe (111) than the Cbenzoyl derivative (HPMBP) .S This paper describes the use of HPMTFP as a reagent which offers a wider pH range and a more sensitive extractive spectrophotometric method for the determination of iron (111) than the 4-acyl-pyrazolone-5 derivative previously reported.'

METHODS AND 'MATERIALS
Apparatus: A Pye Unicam SP6-400 spectrophotometer was used for absorbence measurements. pH was measured with a Kent EIL 7050 ,pH meter. Mixing of phases was carried out with a'Stuart flask shaker.

B A . Uwukwu a~td Belirlda Jack
Reagents: All reagents and solvents used were of analytical grade. Aqueous solutions were prepared with glass distilled water.
HPMTFP was synthesized according to an established method2 and twice recrystallized from aqueous ethanol. The chelating agent was confirmed pure from the following : m.p., 1 3 9 ' C ; calculated for CI2H9O2N2F3 : C, 53.34% ; H, 3.36% , N,  Procedure: A 1 ml sample solution in an extraction bottle containing up to 100 pg of iron (111) was adjusted to a volume of 10 ml and pH 3 with buffer solution (HCVCH3COONa). Ten ml of 0.02 M HPMTFP dissolved in chloroform was added and shaken vigourously for 20 min. The immiscible phases were transferred to a separating funnel and the phases allowed to settle before separation. The absorbence of the intense wine-red organic phase containing the extracted complex species was measured at 480 nm against a reagent blank containing 0.02 M HPMTFP in chloroform. Beer's law was obeyed from 1 ppm to 10 ppm of Fe(II1) extracted into the organic phase.
For other extraction studies , as a function of pH of aqueous solution, a 10 ml solution containing 6 ppm in Fe(ll1) was used. This was adjusted to the desired pH value and extracted with an equal voIume of organic phase containing HPMTFP or a mixture of it and trioctylphosphiie oxide (TOPO) or 2-thenoyltrifluoroacetone (HTTA). For interference studies, the solution containing the appropriate ion was first introduced before adjusting to pH 3.

Absorption spectra
The absorption spectra of 0.02 M HPMTFP and its iron (111) complex species extracted from aqueous solution (pH 3) into chloroform are shown in Figure 1. The extracted iron(II1) complex species exhibited a broad absorbence between 420 nm and 510 nm with a maximum absorbence at 480 nm. Figure 1 shows that HPMTFP does not absorb at 480 nm. Thus, all subsequent studies were carried out at 480 nm.

Extraction and Determination of Fe(II1)
wavelength (d - the mixture has no effect on the colour intensity of the extracted complex species. However, increase in the concentration of TOPO from Mlo-* M in a mixture with 0.02 M HPMTFP showed a significant reduction in the colour suppression from increased TOPO concentration in the reagent mixture. Details of the sensitivity and molar absorptivities of the extracted complex species by the various reagent mixtures are given in Figure 3 and Table 1.

B A . Uzoukwzi and Beli~tda Jack
Soh~e~zts: The use of different organic solvents was studied . The details of the molar absorptivitites of the extracted complex species in these various solvents are contained in Table 1. The Fe(1II) complex is quantitatively extracted by benzene, methyl-isobutylketone (MIBK) and cyclohexanone but the colour of the extracted complex species compared is of slightly lower intensity in these solvent systems when compared to that of chloroform. The colour of the extracted complex species in these solvent systems is stable for days. In cyclohexanone the extracted complex species at low concentration appeared pale brown.

Stability of colour
The stability of the colour of the extracted complex species was studied at room temperature. The maximum absorbence of 0.805 & 0.005 recorded for 6 ppm Fe(1II) extracted into chloroform was measuredat 1, 10, and 30 min and 1,10,24, 48 and 168 h after extraction. The colour of the extracted complex-species was found to be stable for at least a period of one week.
Calibration range and sensitivity .Beer's law was obeyed up to 10 ppm of Fe(lI1) extracted into chloroform. The range increases slightly when solvents such as methyl isobutylketone, benzene or cyclohexanone are used. However, when these solvent systems are used the relative sensitivity also decreases slightly.

Tests for interference
The effects of various ions on the determination of iron(II1) extracted into the organic phase were examined. This was carried out by introducing different amounts of ionic species to a 10 ml solution containing 60pg of iron(I11) at pH 3 and extracting with 10 ml of 0.02 M HPMTFP in chloroform. The absorbence of the extracted complex species was measured at 480 nni against reagent blank. The results are shown ,in Table 2.
Interferences observed from some metal ions came from colour reactions e.g., u6+, cr6+ or formation of emulsion with the extracted complex as was the case with c u 2 + . The interferences observed from some anions were as a result of masking of Fe(II1) in the aqueous phase by these anions which are also complexing agents, e.g., EDTA and oxalate ions.  Table 2 Contd.

Analyses of water samples
The extraction and spectrophotornetric procedures were applied to varidus water samples collected from Port Harcourt metropolis. Each of the sample was subjected to the following method of analysis. 100 ml of the sample in a beaker was evaporated to 10 ml usirig a heating mantle. After cooling, 20 ml of concentrated hydrochloric acid-nitric acid (3:l) mixture was added and the sample heated until digestion was completed. The residue was dissolved in 10 ml 0.1M HN03 . A 5 ml aliquot of this solution was pipetted into an extraction bottle, adjusted to pH 3 with acetate buffer solution and extracted with 5 ml of chloroform solution of 0.02 M HPMTFP. The determination was carried out three times and the results are shown in Table 3. The 4-trifluoroacetyl-pyrazolone-5 derivative is more sensitive and superior to the 4-benzoyl-pyrazolone-5 derivative proposed by Rao and ~rora.' The optimum pH range is also wider than the range obtained by Chmutova and ~o c h e t k o v a~ using the same 4-benzoyl-pyrazolone-5 for their studies. Compared to 0.1 M HPMBP used by these workers4J HPMTFP has proved to be less expensive since 0.02 M of the ligand is more efficient and more sensitive when employed for the same purpose of extraction and spectrophotometric determination of iron(1TT) in aqueous media.