Selective spectrofluorimetric determination of Zn with 5,7-dibromo 8-quinolinol and its application to food and biological samples analysis.

Journal of Molecular Structure, 143 (1986) 549-552 Elsevier Science Publishers B.V., Amsterdam - Printed

SELECTIVE

SPECTROFLUORIMETRIC

AND ITS APPLICATION

P. Ferndndez, Analytical

C. Perez-Conde,

28040 Madrid.

DETERMINATION

OF Zn WITH 5,7-DIBROMO

TO FOOD AND BIOLOGICAL

Chemistry

549

in The Netherlands

A-Ma Gutierrez

Department.

8-QUINOLINOL

SAMPLES ANALYSIS.

and C. Cdmara.

Faculty of Chemistry.

University

Complutense.

Spain.

ABSTRACT 5,7 dibromo-8- quinolinol (L) with Zn(I1) (Ml forms a ML fluorescent complex extractable into ether (A - 410 nm,Xem= 550 nm). This cgmplex is used to provide a sensitive methode?& determination of Zn. The optimum pH is within 5.5 -7.5 and calibration graph is linear up to 1.0 ppm of Zn. The limit of detection is6ngml . The method has been employed to determine Zn in food and biologi-

cal samples. INTROOUCTION The determination cal techniques trition

and

of Zn in food and biological

has become an essential

samples

by different

part of studies concerned

analyti-

with human nu-

toxicology.

At present,

there are several

fluorimetric

methods

ganic samples

(l-3).In this paper a new selective

metric method

to determine

the fluorescent

complex

Zn in biological

and sensitive

samples

Zn-5,7 dibromo8-quinolinol

to determine

Zn in inor-

spectrofluori-

based on the formation

of

is described.

EXPERIMENTAL Reagent and apparatus All chemicals lized distilled -Zn(II)

used in this work were of analytical

stock solution,

unt of Zn(N03J2

reagent

grade.

Deminera-

water was used throughout. 1.12 10v2 M, prepared

in distilled

water.

tion with EDTA. Dilute standard

by dissolving

Its concentration

solutions

the appropiate

was determined

were prepared

amo-

by a titra-

daily by diluting

this

stock solution. -5,7 dibromo-8-quinolinol -Hexametilentetramine The fluorescence spectrofluorimeterwith

re adjusted

(HBQ) solution,

0.5% w/v in acetone.

(HMTA) 2.5 M-perchloric measurements

acid buffer pH 6.0.

were made with a Perkin

1 cm quartz cells and a xenon-arc

to give a IO nm band,

in both

the excitation

chromators.

0022-2860/86/$03.50

0 1986 Elsevier Science Publishers B.V.

Elmer Model MPF-44A

source.

Slit-widths

and the emission

wemono-

550 Procedure Mineralize -H2S04-HN03

the horse kidney and animal muscle

1:1:3 mixture

gen Microwave

samples

funnel.

3M ammonia solution

Add in order given, to neutralize

up to 10,~~ of Zn into a

1.1 ml of HBQ solution,

the excess acidity

several

water. Add 10 ml of diethylether

nnel for 2 min. tensity

Inmediately

(A ex = 410 nm,X,,

pared in parallel. Zn(I1) treated

RESULTS Spectral

AND

Prepare the calibration

the fu-

the fluorescence

extract

against

graph by using standard

in-

a blank pre-

solutions

of

DISCUSSION

The complex

excitation

the Zn by shaking

measure

= 550 nm) of the organic

bu-

10 ml with

in the same way.

characteristics

fluorescence

and extract

after phase separations

drops of

and 4 ml ofH2MTA+/HMTA

ffer. Adjust the final volume of the aqueous phase to approximately distilled

with HC104

in an R.F. Oxi-

Plasma.

Pipette a portion of the sample solution containing separating

by digestion

(4) and ash the H-9 human diet sample

of compllex

Zn-5,7 dibromo-B-quinolinol

emission

at 550 nm when

and emission

400

it is excited

nm

of

at 410 nm. The uncorrected

4

Fig. l.Fluorescence excitation and emission spectra of the Br -Ox-Zn chelate (I, III) and the &agent blank (II, IV)

The optimum

shows a maximum

spectra can be seen in Fig. 1.

600

Effect of experimental

in diethylether

8

12

pH

Fig. 2. Effect of pH on fluorescence intensity for the: (I) reagent blank and (II) Br -Ox-Zn chelate. The pH was adjusJed wi?h (0) HCOO-CH /CH -COO-, (x) H2MTA/HMTA, (0) NH4C1?NH33 (4)NaOH.

variables

pH for the formation

of the

fluorescence

complex

is between

5.5

551 and 7.5 (Fig.2). The HMTA buffer solution was selected because it provides the minimum fluorescence of the blanks. The concentration of reagent used was 1.8 10_3M. The study of influence of the ionic strength of the medium carried out by adding variable and increasing amounts of NH4N03 shows that blanks fluorescence intensity increases with the ionic strength while that of the complex, until p=

0.25, remains constant. For a value of/I" higher than 0.25 the complex emis-

sion fluorescence decreases. Stoichiometryof the complex The stoichiometry of the Zn-5,7 dibromo-8-quinolinolfluorescent complex was evaluated by the usual methods: continuous variations, mole ratio, Asmus and slope analysis. The results obtained by these four methods were completely in agreement and showed that the M:L relationship is of the type 1:2. This stoichiometry ratio was in agreementbuiththe one obtained by Navratil et a1.(5) who studied the same complex extracted in chloroform using the spectrophotometry technique. Analytical characteristicsof the spectrofluorimetricmethod The calibration graphshowed a linear relationship between the emitted fluorescence intensity and the Zn(II) concentration up to 1.0 ppm of Zn. The variation coefficient evaluated from eight independentdeterminations at the 0.2 ppm Zn level is 3.5%. The detection limit was given by the equation (1) CL = K SbL/S

(1)

where K is a numerical factor chosen according to the confidence level desired, SbL is the standard deviation of the blank measurements and S is the sensitivity of the calibration graph. For nB = 11, a CL value (K = 3) of 6 ng ml-' was obtained Interferences The effects of 31 potential

interfering species on the proposed method we-

re examined. The ions under investigationwere added to aqueous solutions containing 8,&g of Zn. Each test solution was treated by the determination procedure and the results are shown in Table I. Fe and Ca resulted the main interferents for the samples to be analised. A concentrationof Fe twice of the Zn can be tolerated by adding an excess of reagent of 150 times the concentration of Zn. The interferenteffect of Ca

can be eliminated by adding F-. The CaF2 precipitated

does not interfere and a concentration of Ca 350 times higher than that of Zn can be tolerated. The presence of organic material drastically interfered in the proposed method. Therefore its full elimination before Zn determination is essential. Applfcations The method described was applied to the determination of Zn in whole human diet and some biological materials. The results obtained are summarised in Ta-

562

ble II. There are not significant differences between the values obtained and the values certified at the 95% confidence level. Therefore, it can be concluded that the proposed method is very simple, selective and sensitive for the determination of Zn in human diets and biological samples. TABLE

I

Tolerance limits for diverse ions in the determination of Zn (0.8 ppm) Ions

Tolerance foreign ion/Zn,w/w

po3- so,, clNa4 ’ K, CO= Be, Ca, Sr, H2CitCa

Ions

Tolerance foreign ion/Zn,w/w

1000* 7!io* 500* IO 7

* Maximum ratio tested TABLE

II

Zn content in human diet and some biological samples Sample*

Zn$ found .ys'g

Horse Kidney (a) Animal muscle (a) Whole diet H-9 (b)

189 88 28.6

V.C.

::: 3.0

Certified /AgIg 192+13 86 ____

* (a) and (b) refer to the use of H2S04-HC104-HN03mixture and low temperature dry ashing respectively # Average of six determinations. REFERENCES

1 M. Santiago, A. Navas, J.J. Laserna and F. Garcia Sanchez, Mikrochim. Acta 2 3 4 5

II, (1983), 197-204. M.R. Martinez de la Barrera, J.J. Laserna, F. Garcia Sanchez, Anal. Chim. Acta, 147 (1983) 303-309. A. Perera, A.M. Santana, J.J. Garcia Montelongo, Microchem. J.,29(1984) 113118. A.M. Gutierrez, C. Perez Conde, M.P. Rebollar and L.M.Polo Diaz, Talanta (In press) 0. Navratil and J. Kotas, Collection Czech. Chem. Commun, 30(1965),1824-1831

ACKNOWLEDGMENTS We whish to thank to the C.A.I.C.Y.T. for the support of this work under the contract number 1710/82