Flow-injection determination of zinc by fluorescence spectrometry

Anolytrca Chmnca Acta, 255 (1991) 325-328

325

Elsevler Science Publishers B V , Amsterdam

Flow-injection determination of zinc by fluorescence spectrometry R Compaii6, S Hemiindez-Cassou and M D Prat * Departament de Quikca Analitaca, Unwersatatde Barcelona, Dtagonal647, 08028, Barcelona &am)

L Garcia-Belt&n ServadeBwquinuca,

Hospztal General C S Vail d’Hebron, Pg Vail d’hlebron s/n,

08035, Barcelona (@am)

(Recewed 14th May 1991, revised manuscript received 11th July 1991)

AbSh7Wt

A flow-mn~ectm method IS descriied for the determmahon of zinc m the range lo-600 pg I-‘, based on the fluorescence of the zmc-5,7-d~chlorc+2-methylqurnohn-8-ol chelate m a Bq-35 rmcellar medmm The detection hxmt is 3 pg Zn I-’ and the sample throughput IS 180 h-’ The method was evaluated for the deternunatlon of zmc m pharmaceutxal preparations and III tap water k?ywords Fluonmetry, Flow system, Pharmaceuticals, Waters, Zmc

Contmuous-flow methods, in particular flowinJection analysis @‘IA), have advantages that make them smtable for use m routme analysis m different areas Several FIA methods have been described for the determmation of zmc usmg detectlon techmques such as molecular spectrophotometry [l-43, atomic absorption spectrometry (AAS) [5-81, plasma atomic ermsslon spectrometry [9,10], amperometry Ill] and strippmg potentlometry [12] A method based on the mhlbltlon of a chemllummescent reactlon has also been reported 1131 Although many batch fluonmetnc methods for the determmatlon of zmc have been described 1141,no reference was found to any FIA procedure for the determmatlon of this metal Ion by fluorescence spectrometry Thus paper describes an FIA method based on the highly fluorescent complex of zinc with 5,7-dlchloro-2-methylqumolm-8-01 (DCMQ) m a BrlJ-35 mlcellar mednnn [15] Thus method offers better senntrvlty and detectlon hnut than those usmg

AAS detectron and, although It IS non-specific, the mterferences are not severe This FIA system conslderably srmphfies sample and reagent mampulatlon and IS a means of rapldly performmg se& analyses wlthout a loss of sensltlvlty with respect to the manual procedure It can be apphed to the monrtormg of zmc m tap waters and m pharmaceutical preparations

EXPERIMENTAL Reagents

A stock standard solution of zmc mtrate (1 g Zn I-‘> was prepared and workmg standard solutions were prepared daly by dllutlon wth 10e3 M mtric acid 5,7-Dlchloro-2-methylqumohn-8-01 (DCMQ) (Supro, Troponwerke, Koln, Germany) was punfled as described [16] and 1 X low3 M solutions m ethanol-water (40 + 60, v/v> were prepared dally

0003~2670/91/$03 50 0 1991 - Elsevler Snence Pubhshers B V All rshts reserved

R COMPti6

326

ET AL

Buffer solution (pH 6 1) of succm~ acldsodium succmate (0 04 M) was prepared Maskmg solutions of pH 6.1 (succmlc acid) contammg sodmm thlosulphate (0 1 M) and/or sodium pyrophosphate (10m3 M) were prepared A surfactant solution of BIIJ-35 (1 X 10m2 M) was used Doubly delomzed water (Culhgan Ultrapure GS) was used throughout Apparatus

A Perkm-Elmer MPF-66 spectrofluornneter Hrlth a Hellma flow cell (25 ~0, a Perkm-Elmer Model 4000 atomic absorption spectrometer, a Selecta Tectron thermostatic bath and a Radlometer PHM 64 pH meter were used Flow system and measurement procedure

A three-channel mamfold with a perlstaltlc pump (Scharlau HP4) and a variable-volume electncal mjectron valve (Slrtek, MV-8) was used Standard Tygon pump tubing was used for aqueous solutions of Br1~-35 and buffer, and DCMQ solution was delivered through Solvaflex pump tubing The total flow-rate was 3 3 ml mm-l and the mdlvldual flow-channel ratios were 5 5 1 (surfactant buffer reagent) For all connections 05 mm 1 d PTFE tubmg and PTFE standard T-pieces were used The sample (58 ~1) was inJected after mergmg of surfactant and buffer and before its reaction with the reagent (Fig lb) Fluorescence was measured at 534 nm, usmg excitation at 397 nm Sht Hrldths were adJusted to 15 nm m both monochromators

RESULTS

Prehnmy

AND DISCUSSION

stdes

The development of the reaction was mvestlgated by usmg various three-channel mamfolds The highest peaks were obtamed when the three channels merged before the sample was mJected (Fig la) When msertlon was camed out according to Fig lb the response decreased slightly, whereas other schemes, Hnth mjectlon mto the buffer or surfactant flows, gave a marked decrease m the signal

Fg

1 Flowqectlon mamfolds used 1, Buffer solution, 2, solution, 3, DCMQ solution, S, sample solution, L, and L,, reactlon cods, D, detector, P, penstalk pump

Br1~-35

In the batch procedure 1153, it was observed that addition of maskmg agents (thlosulphate and pyrophosphate) unproved the selectlvlty of the method Therefore, the mamfolds m Fig la and b were used to test most mterfermg ions, usmg buffer solutrons contammg the appropriate maskmg agent Dtierences m the results for each manifold result from the reaction of the sample wth the maskmg agent, d this 1s introduced before or slightly after the reaction Hnth DCMQ The results mdlcated that m the mamfold m Fig lb the maskmg agent was more efficient, and this arrangement was therefore adopted Injhence ofchemrcal vanabh A maxunum and constant analWca1 signal was obtained over the pH range 5.8-75. A pH of 6 l-6 2 was chosen m order to improve the seleo t1vlty The peak height m&eased with mcreasmg reagent concentration, but the ethanol-to-water ratio necessary to avold preclpltatlon was a lmtmg factor At ethanol contents lower than 30% DCMQ preclpltated m the FIA system, and for contents greater than 60% the solutions had to be degassed A reagent concentration of 1 X 10e3 M m ethanol-water (40 + 60) was selected The BIIJ-35 concentration had no influence on the fluorescent signal over the range 4 X 10w3-2 X lo-* M W-220 tunes the crltlcal mlcelle concentration) The fluorescence signal decreased shghtly with mcreasmg temperature A coefflclent of 1% “C-l was obtamed between 15 and 30 o C

FL% OF

ZINC

Optunlzatwn of FL4 parameters The analytlcal signal increases Hrlth mcreasmg

sample size, but for volumes greater than 50 ~1 it remains constant The peak he&t increases as reactlon co11L, IS shortened, whereas the length of co11 L,, over the range 30-120 cm, had no influence The selected values for L, and L, were 60 and 30 cm, respectively Two values of the inner diameter of the whole FIA system tubmg (0 7 and 0 5 mm) were tried, and the latter gave better results The FIA signal was not affected by varlatlons m the total flow-rate over the range l-6 ml mu-‘, provided that the mdlvldual flow-rate ratios of buffer surfactant reagent were kept constant at 5 5 1 Churacterrstlcs of the method

Under the condltlons outlmed above, the cahbratlon graph of peak height vs concentration 1s hnear over the range lo-600 pg 1-l The relatwe standard devlatlon for two senes of fifteen solutlons contammg 200 and 40 pg Zn I-‘, each bemg injected m triplicate, was 1 8% and 4 3%, respectively The detection hmlt, calculated as the concentration gwmg a slgnal three times the standard devlatlon of twenty measurements on a standard 4 pg 1-l zmc solution, was 3 pg l-l, and the hmlt of determination was 10 yg I-’ These results agreed with those calculated for three and ten times the slgnal-to-noise ratio, respectively The sample frequency was 180 h-’ Interferences The mfluence of foreign ions was tested at a

zinc concentration of 200 pg I-’ The crlterlon for interference was fared at f5% The FIA results, compared with those obtained m the manual procedure, are given m Table 1 The tolerance hnuts are slmllar 111the two methods, Al(III), Nl(II) and Pb(I1) showmg the highest differences Thus, whereas the mterference from AK1111Increased when the FIA method was used, those from N&II) and Pb(I1) were markedly reduced Although thlosulphate IS less effective as a maskmg agent for Cd(H) and Pb(II), the method has a satisfactory selectlvlty level, because when maskmg agents were used, only Co011 and Cd(I1)

327 TABLE 1 Maxmmm tolerance ratios of foreign Ions to zmc at a zmc concentration of 200 pg 1-l Ion added ClO,-, NO;, SO:-, Na+, K+ ClBO;, Br-, F-, I-, Ba*+, Ca*+, Ll+, NH: PO,3 Mg’+ Ml?+ Be*+ Hg’+ Ag+ Al3+ FE?+ NI’+ Coz+

Batch procedure

mA procedure.

20000 ’ 10000

2OOoO= 10000

cuz+ PbZ+ Cdz+ T14+

lOOOn 1000 B 500 25 10 5 5 5 25 25 1

1000B 750 250 50 10 2 5 1 1 20 2

1OOOb 1OOOb 5OOb 50 c 25’

<05 05 <05 05

:I 50b 5c

1oOOb 250b 5OOb 20 c 25=

05 5 05 05

2:: lb 25c

a The highest ratlo tested b Maskmg thmsulphate solutlon ’ Maskmg pyrophosphate solution

Interfered at concentrations comparable to those measured for zmc Detemunatlon of zmc m real samples The FIA method was evaluated with respect to

flame AAS for the determmatlon

of zmc m tap

TABLE 2 Determmatlon

of zmc m real samples

Sample

Collyna 1 (g I-‘) CollynaZ(gl-‘) Collyna3(gl-‘1 Mouthwash 1 (g I-‘) Mouthwash 2 (g I-‘) Insuhn 1 (mg I-‘) Ins&n 2 (mg I-‘) Tap water 1 (fig 1-l) Tap water 2 (pg 1-l) Tap water 3 (pg 1-l)

Zmc concentration Proposed method a

AAS *

Label value

024*001 043*001 119*002 138*003 098*002 835 *11 785 k14 77 *2 127 f 2 61 kl

026*001 044f002 1 16fO 03 133*003 095*003 820 f13 774 *15 74 *4 131 *4 62 +4

023 045 1 13 144 0 96 80 80

B Means of five determmatlons

f standard devlatlons

R COMPA6IO

328

water and m cxxnrnerclal pharmaceutical preparatlons Mouthwashes and collyria were aqueousethanohc or aqueous solutions which also contamed antibiotics, sulphamldes, cortlcolds and/or adrenerglc agents Insulm formulations were aqueous suspensions of porcine pancreas or human msulm These samples were dduted with 1 X 10m3 M nitric acid and then mJected directly mto the FIA system without using maskmg agents Water samples were analysed mthout maskmg agents and also usmg a buffer solution contammg thlosulphate (0 1 M) and pyrophosphate (1 X 10m3 M) and no slgmficant differences were observed The results are given m Table 2 and are m good agreement urlth those obtained by flame AAS and the values stated by the manufacturers The authors thank the ConnsGn para la Investlgacl6n Clentifica y TBcmca (CICYT) for supportmg this study (Project PB87-0059)

ET AL

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