Determination of Trace Elements in Pharmaceutical

8/13/2019 Determination of Trace Elements in Pharmaceutical

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.Spectrochimica Acta Part B 54 1999 827 833

Determination of trace elements in pharmaceuticalsubstances by graphite furnace atomic absorption

spectrometry and total reection X-ray uorescence

after ow injection ion-exchange preconcentration A. Kelko-Levai, I. Varga, K. Zih-Perenyi, A. Lasztity

Department of Inorganic and Analytical Chemistry, L. Eot os Uni ersity, P.O. Box 32, Budapest 112, H-1518 Hungary

Received 5 October 1998; accepted 9 February 1999

Abstract

.Flow injection iminodiacetic acid ethyl cellulose IDAEC microcolumn preconcentration and graphite furnace .atomic absorption spectrometry determination of trace metals Cd, Co, Ni, Pb were carried out without decomposi-

. .tion of the drug matrix. The two forms of chromium Cr III and Cr VI were separated using IDAEC and anion .exchanger diethylaminoethyl DE -cellulose, respectively. The detection limits of trace elements in pharmaceutical

.substances sugars, sorbitol, mannitol, paracetamol, amidopyrine, chloral hydrate after a 10-fold preconcentration in1 5% m v solution of pharmaceuticals were in the 0.3 29 ng g 1 range. The measured concentration of traceelements in substances investigated was below 100 ng g 1. The spike recovery was close to 100%. The capability of total reection X-ray uorescence technique for the determination of trace elements in pharmaceuticals with and without preconcentation was explored. 1999 Elsevier Science B.V. All rights reserved.

Keywords: ETAAS; TXRF; Flow injection; Preconcentration; Impurities; Drugs; Speciation; Cr

This paper was published in the Special Issue of the Third European Furnace Symposium, Prague, Czech Republic, June 1998.Corresponding author. Fax: 36-1-209-0602.

0584-8547 99 $ - see front matter 1999 Elsevier Science B.V. All rights reserved. .PII: S 0 5 8 4 - 8 5 4 7 9 9 0 0 0 3 6 - 1


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( ) A. Kelko-Le ai et al. Spectrochimica Acta Part B: Atomic Spectroscopy 54 1999 827 833 828

1. Introduction

In the quality control of drugs and medicines,

determination of inorganic impurities is impor-tant. Some of these trace elements are toxic,some of them even in ultratrace concentrationscould decrease the stability of active ingredients.Some of the impurities could be indicators of non-adequate handling and storage or be used asngerprints for the source of drug crude material.

Heavy metal tests are included in all pharma-copoeias. They are non-specic tests for metalsbased on the formation of coloured sulphidespecies. These tests are not universally applicable

to check for all potential heavy metals catalysts:Pd, Pt, Rh; or impurities from stainless steel. vessels: Cr, Fe, Ni, etc. and the used reagents

H S and thioacetamide are toxic. Because the2sensitivity and selectivity of these tests in mostcases is not sufcient for the recent industrialrequirements, the determination of trace inor-ganic impurities by instrumental methods has be-come more important for the quality control of pharmaceutical substances.

For some substances, e.g. sugars, the test limit 1 .for lead 0.5 g g is specied in the Euro-

pean Pharmacopoeia 1 . Prior to analysis bygraphite furnace atomic absorption spectrometry .GFAAS the sugar sample has to be decomposedin a polyuorocarbonate bomb for 5 h at 150 Cbecause a direct analysis is difcult due to highcontent of organic matter. In compounds synthe-sized with Pd catalysts, Pd is also determined by

GFAAS 2 , inductively coupled plasma-mass .spectrometry ICP-MS and axial inductively cou-

pled plasma-atomic emission spectroscopy ICP-. AES techniques 3,4 . Lewen et al. 5 examined

ICP-MS and axial ICP-AES as an alternative tothe USP heavy metal test. Total-reection X-ray

.uorescence spectrometry TXRF is a multi-ele-ment method with low detection limits, smallsample mass requirement and simple quantica-

tion in a wide dynamic range 6 . Its rst applica-tion in drug analysis was for the discriminationbetween batches of the same pharmaceuticalproduct originating from different production orpurication processes by their element nger-

prints measured by TXRF directly or after diges- tion of samples 7 .

The matrix of pharmaceuticals has a big varietybecause of their different chemical composition.In many cases direct measurement of trace ele-ments without decomposition of the matrix couldnot be accomplished either by GFAAS or TXRF.Coupling a preconcentration step to GFAAS andTXRF could reduce the matrix effect, improvethe sensitivity, and could avoid the tedious andtime-consuming sample decomposition of sub-stances. A separation allows also to distinguishbetween anionic and cationic forms of metals andthus to investigate possible interactions betweenthe drug matrix and metals. Iminodiacetic acid

.ethyl cellulose IDAEC chelating ion exchangerhas ideal properties to be used in ow injection .FI on-line systems as microcolumn lling formulti-element preconcentration of trace metals

8 . Stability constants of metal IDAEC chelates were determined and used to predict the sorptionof ultratrace elements from highly mineralisedmedicinal waters on a FI microcolumn for pre-concentration prior to their spectrochemical de-

.termination 9 . Chromium-III and Cr VI con-tents in rain water samples were determined us-

.ing IDAEC and diethylaminoethyl DE -cellulose for preconcentration 10 .

The aims of this work were:

1. to study the possibility of using a FI-IDAECmicrocolumn preconcentration procedure forseparation of trace metals from drug matricesprior to their GFAAS and TXRF measure-ment;

2. to develop a screening metal test using directTXRF method or coupling it with FI-micro-column preconcentration; and

. .3. to determine Cr III and Cr VI levels indrugs by preconcentration on IDAEC andDE-cellulose microcolumns.

2. Experimental

2.1. Reagents

Throughout the study, high-purity water dis-


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.tilled water puried on ion-exchange celluloses was used. The ammonium acetate buffer solution was prepared by isotherm distillation. All reagents were of analytical grade. AAS metal standards

1 1.000 g l supplied by Merck Darmstadt, Ger-.many were used for preparation of calibration

solutions. IDAEC was synthesised from ami- noethyl cellulose 11 . The copper capacity of the

exchanger was 0.8 mmol g 1. The capacity of . 1DE-cellulose Whatman was 1.0 mmol g .

The pharmaceutical substances analysed are .sugars sucrose, glucose, lactose , sorbitol, manni-

tol, amidopyrine 4-dimethylamino-1,5-dimethyl-.2-phenyl-4-pyrazolin-3-one , chloral hydrate and

indomethacin.

2.2. Instrumentation

A Perkin-Elmer Model 3110 atomic absorptionspectrometer with deuterium background correc-tor, a Perkin-Elmer HGA-600 graphite furnace with pyrolytic graphite coated tubes and Lvovplatforms, and a Perkin-Elmer AS-60 autosam-pler were used. All measurements were run with20 l sampling volumes using gas stops and inte-

grated absorbance readings during the atomiza-tion step. Operating conditions and analyticalparameters are listed in Table 1.

TXRF measurements were performed on

. Atomika EXTRA IIA Germany spectrometer.Operating conditions were as follows:

Excitation: line-focused X-ray tubes, Be win-dow; Mo anode excitation energy: 17.5 keV, 200

. m Mo cut-off lter ; W anode excitation en-.ergy: 35 keV, 300 m cut-off Ni lter . Mo or W

tube operated at 50 kV and 25 mA. Incident .angle: 6 . Detection: Si Li detector; 2000 channel

.analyser, resolution: 0.16 keV at 6 keV . Measur- .ing time: 600 s. Analytical lines in keV : Cr K

5.41; Fe K 6.40; Co K 6.93; Ni K 7.47; Cu .K 8.04; Zn K 8.63; Pb L 10.55 Mo anode ;

.Cd K 23.11 W anode .The samples were spiked with 200 ng ml 1 Sr

.as internal standard and dried 10 20- l aliquots

on pre-cleaned quartz glass carriers.

2.3. Preconcentration

.Preconcentration of Cd, Co, Cr III , Ni and Pb . was performed by on-line ow injection FI on a

microcolumn lled with 40 mg of IDAEC inNH -form. The drug samples were dissolved in4 water, in case of paracetamol in a 20% v vmethanol water mixture to get a 1 5% m v so-

lution. A dual four-way valve assembly was ap-plied for preconcentration and elution of trace 1elements 9 . The eluent was 2 mol l HNO at3

ow rate 2.0 ml min 1. The eluates were col-

Table 1Measuring conditions

Temperature program Cd Co Cr Ni Pb228.8 nm 241.0 nm 357.9 nm 232.0 nm 283.3 nm

.Drying C 110 110 110 110 110

.Ramp hold time s 10 10 10 10 10 10 10 10 10 10 .Drying C 180 180 130 180 180 .Ramp hold time s 10 20 10 20 1 35 10 20 10 20

.Pyrolysis C 500 1400 1650 1400 700 .Ramp hold time s 1 30 1 30 1 30 1 30 1 30

.Cooling C 20 20 20 20 20 .Ramp hold time s 1 15 1 15 1 15 1 15 1 15

. Atomisation C 1500 2500 2500 2500 1900 .Ramp hold time s 0 5 0 5 0 5 0 5 0 5

Gas ow at atomisation Gas stopa .Modier 0 0 0.05 mg Mg NO 0 03 2

a 5 ml of 1% m v solution.


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Table 6TXRF determination of metals after IDAEC-microcolumn preconcentration

Element Preconcentration Preconcentration S.D. 10 times S.D. . .blank blank spike n 3 preconcentrated n 3

1 1 . .200 g l 20 g l

Cd Not detected 182 18.0 202 17.0Co Not detected 213 17.1 218 12.4Cu 20 224 19.4 182 14.9Fe 30 205 18.3 220 6.1Ni 30 226 7.2 232 3.1Pb 20 208 8.3 224 6.7

Note. Results in g l 1 .

of TXRF method and to avoid the sample diges-tion step the same preconcentration procedure asfor GFAAS was used. To test the effect of theeluate matrix on the TXRF measurement resultsfrom a preconcentration blank spiked with 200

g l 1 metal solutions were compared with the10-fold preconcentrated 20 g l 1 metal solu-

.tions Table 6 . The results show that the sorption was above 90% for most of the elements investi-gated. The standard deviations were calculatedfrom three separate measurements.

The substances analysed by GFAAS and TXRFare the same. Other elements preconcentrated on

.IDAEC Cu, Fe, Zn, etc. can be determined inthe same way. The found level of impurities formost of the elements was lower than 0.5 g g 1.

The recovery of spike additions of 80 1000 ngg 1 after preconcentration on the IDAEC micro-column was also checked. The concentration of

spikes in individual drugs is usually one order of magnitude lower than the specied heavy metal

.limits Table 5 . The recoveries presented in Table7 are better than 70%, though with high uncer-tainty due to high background. To get more accu-rate results, larger additions, longer measuringtime or a higher preconcentration factor shouldbe used.

For substances not soluble in water or in wa- .ter methanol ethanol mixtures a direct TXRF

method can be used. As an example, the tracemetal level in indomethacin was determined usinga 1% m v solution of the drug in acetone. The

recoveries of 100 ng ml 1 spikes of all the ele- .ments see Table 8 are acceptable considering

that the limit value of the Heavy Metal Test is 10g g 1.Detection limits of elements in the eluate as

derived from spectral background noise when us-

Table 7Spike recovery of elements on IDAEC microcolumn from pharmaceutical substances by TXRF

. . . .Substances Cd II Co II Ni II Pb II

Added Found Added Found Added Found Added Found

Glucose 80 90 200 212 100 74Lactose 80 95 200 167 100 122Sucrose 80 100 200 180 100 94Sorbitol 100 82 100 132 100 127Mannitol 100 72 200 210 100 137

a Amidopyrine 20 25 400 440 1000 770 500 472aParacetamol 20 27 400 395 1000 955

aChloral hydrate 20 19 400 350 1000 760 500 370

Note. Results in ng g 1 ; concentration of samples: 5% m v.a Concentration: 1% m v.


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Table 8Spike recovery from 1% m v solution of indomethacin bydirect TXRF

Metals 1% indomethacin 1% indomethacin1 1 . .found ng ml spike 100 ng ml

1 .found ng ml

Co 20 107Cr 20 86Cu 20 104Ni 25 96Pb 30 126

Note. Indomethacin was dissolved in a mixture of acetone1 . 1and 1 mol l HCl 98 2 ; 200 ng ml Sr internal standard.

ing samples of only 20 l of eluate and 600 s

measuring times during TXRF analysis werefound to be at 10 g l 1 level.

4. Conclusions

A FI-IDAEC microcolumn preconcentrationhas been coupled to GFAAS for the determina-tion of heavy metals in sugars and drugs. Thisprocedure separates, and enriches trace metalsfrom pharmaceutical substances without decom-position of the matrix thus improving sensitivityand eliminating matrix effects in GFAAS de-terminations. Quantitation at ng g 1 levels ispossible. Using different cellulose ion-exchangersfor the preconcentration the ionic state of chromium in pharmaceutical products can be ver-ied and quantied.

The multielement TXRF method with or with-out preconcentration can provide an element spe-cic screening procedure for heavy metals as wellas for all other potential elements and inorganicimpurities.

Acknowledgements

We would like to thank Toth Karolyne for her technical assistance. The research was sponsoredby the National Foundation of Scientic Re-

.search OTKA No. A196 95 450 .

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Determination of Trace Elements in Pharmaceutical

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