Direct determination of selenium in a wild fruit juice by electrothermal atomic absorption spectrometry

Talanta ELSEVIER

Talanta

43 (lYY6)

Y85%98Y

Direct determination of selenium in a wild fruit juice by electrothermal atomic absorption spectrometry Y ongming Dalian

Instirttrr

Liu *, Benling Gong, Zhuanhe

of Cltemic~al

Received

P/t~~si~~s. .At~udmttu

18 July

1995: revised

Sinrca.

Li, Yuli Xu, Tiezheng Lin

I6 I Z/ton&tart

24 October

Road.

1995: accepted

Dalian.

People

27 October

LF Rqtuhlk

of

Cltirtu

19Y5

Abstract A matrix modifier composed of platinum and nickel is proposed for the determination of selenium in a wild fruit juice made from Lantingguo ( Vuccini~n uliginosmt ). Five matrix modifiers (copper/nickel. palladium/magnesium. platinumlmagnesium. platinumnickel and platinum/copper) for suppressing the interference effects of seven co-existing elements (potassium. phosphorus, calcium, magnesium, manganese, zinc and iron) in a wild juice were studied and a matrix modifier composed from 10 pg of platinum and 200 Llg of nickel was found to give the best performance. Selenium in three juices was determined by electrothermal atomic absorption spectrometry employing the proposed matrix modifier without matrix preseparation. The relative standard deviation was 14% for 0.20 mg 1~~’ of selenium. The recoveries were 955110%. A characteristic mass was 28 pg.

Kqwwds: Selenium; Matrix

modifier:

Electrothermal

atomic absorption

1. Introduction A wild fruit juice made from Lantingguo ( VWcinium uliginosum) which grows in the mountainous area of north-east China is a natural nutrient. It contains many kinds of amino acids, vitamins and essential elements, including selenium. Selenium is an essential element in the human body. It is now recognized that deficiencies of selenium are associated with heart disease,muscular dystrophy, reproductive disorder and some cancers. * Corresponding author. Fax: + 86 41 I 3632426 0039-9140/96~S15.00 SSDf

,C’ 1996 Elsevier

0039-9140(95)01800-X

Science

B.V. All rights

reserved

spectrometry

In order to estimate the content of selenium in the wild fruit juice mentioned above, we studied the method for determining selenium. Electrothermal atomic absorption spectrometry was chosen for this purpose as the content of selenium may be low. The juice has a very complicated composition, in which the comparatively large amounts of potassium, phosphorus, and iron interfere severely with the determination of selenium by electrothermal atomic absorption spectrometry. The separation of selenium from such a complicated matrix would be unlikely to succeed. Only the application of a suitable matrix modifier would overcome the matrix interference.

986 Table I Instrumental (a) Instrumental

I’. Liu tv ul.

parameters

and operating

3

(1996)

985-989

conditions

parameters

Wavelength (nm) Spectral band-pass (nm) Lamp current (mA) Integration time (s) Mode Background corrector Injected sample volume (111) (b) Heating

Tulunr~r

196.0 2.0 8 6 Peak height Deuterium arc IO

programme

Parameter

Temperature (“C) Ramp time (s) Hold time (s) Read time (s) Internal gas flow rate (ml min

Step

‘)

I

2

3

3

120 IO 20

600 IO 20

1200 IO 20

1300

300

300

300

Up to date, a number of matrix modifiers have been proposed for the determination of selenium in various matrices, for example nickel [l-4]. copper [1.5], palladium [6-81. molybdenum [9]. silver [lo], lanthanum [9]. zirconium [ll], copper/ magnesium [ 11I 121. copper/iron [13,14], nickel/ magnesium [ 151, palladium:‘ascorbic acid [ 16- 181, palladium/magnesium [ 17,191, palladium/copper [20], palladium/vanadium [21], palladium/albumin [22], platinum,‘nickel [23], platinum/copper [23]. Saeed and Thomassen [24] used platinum as a matrix modifier for determining selenium in urine which contained phosphorus and iron. They found that platinum could decrease the overcompensation effect of these two elements when a deuterium arc background corrector was used. Bauslaugh et al. [25] proposed a mixed platinum, nickel matrix modifier to control the problems arising both from the thermal instability of selenium and the spectral interferences of phosphorus, iron, etc. in the determination of selenium in whole blood. urine and acid-digested biological materials. A matrix modifier to suppress the spectral interferences of large amounts of potassium was not found in the literature.

-

5

1 3 0 0

6

2600 I 3

20 I 3

300

300

2. Experimental 2.1. Appurutus A Perkin-Elmer Model 5000 atomic absorption spectrometer equipped with a Model HGA 500 graphite furnace, a Data Station 10 and a PR 100 printer was used. A selenium hollow cathode lamp made in the Hengshui Ningqiang Light Source Factory (Hebei, People’s Republic of China) and a Perkin-Elmer pyrolytic graphite tube were used. Instrumental parameters and operating conditions were optimized by means of experiments and are shown in Table 1. 2.2. Rrugrrm All chemicals used were of analytical grade, and distilled, deionized water was used throughout. A stock standard solution of selenium (1000 mg 1~ ‘) was prepared by dissolving 1.4050 g of selenium dioxide and diluting to 1000 ml with water. The working standard solutions were prepared by successive dilution of the stock standard solution to final concentrations (0, 20. 40, 60 pg 1~ ‘) with 0.2% nitric acid solution.

Y. Liu et ul.

Permissible

amounts

Modifier

Ni/Cu Pd:Mg Pt;Mg Pt/Ni Pt/Cu

Amount

of seven co-existing

amount

(/rg)

33 (1996)

usmg the followmg

Permissible

used (pg)

(203 IO) (3020) (10;50) (lo;?oo) (lO~?OO) Maximum

elements

Taluntu

amount

988-989

matrix

modifiers

(icg) of co-existing

element

987

for the determination Characteristic

K

P

Ca

Mg

Mn

Zn

Fe

25 50 50 IO0 100

1.25 0.06 0.03 IO 1.26

25 5 5 50 50

IO

IO 5 5 5 5

IO 5 -.‘5 5 5

2.5 0.5 0.5 1.5 I

4

0.4

of co-existing 20

4

element

20 10 m real juice

4

4

of 0.4 11g of selenium mass (pg)”

27 Ii 21 28 26

sampleh 4

*The mass of an analyte element that generates a signal of I’:;# net absorption (0.0044 absorbance). b The amount contained in a IO ,uI aliquot of the sample solution prepared from IO g of sample.

A 1 g 1~~’ solution of platinum, a 20 g 1 ’ solution of nickel, a 3 g 1 ’ solution of palladium, a 20 g l- ’ solution of copper and a 5 g 1~ ’ solution of magnesium were prepared for the preparation of the matrix modifiers. A mixed matrix modifier was prepared by mixing equal volumes of a 1 g 1~ ’ solution of platinum and a 20 g 1~ ’ solution of nickel. A 10 g 1~. ’ solution of potassium. a 1 g 1~ ’ solution of phosphorus, a 5 g I- ’ solution of calcium, a 2.5 g l- ’ solution of magnesium. 1 g 1~ ’ solutions of zinc and manganese, and a 0.25 g l- ’ solution of iron were prepared for the study of the interferences. 2.3. Prowhire

About 10 g of fruit juice sample was weighed into a 250 ml beaker and 20 ml HCL-HNO, mixture (3:l) was added. The sample solution was heated on a hotplate until the organic component was completely decomposed. After cooling, the sample solution was transferred to a 25 ml volumetric flask and diluted to the mark with water. A 10 ~1 aliquot of the sample solution and a 20 yl volume of the mixed matrix modifier were injected into the graphite furnace, and the peak height was measured.

3. Results and discussion

Preliminary analysis shows that this wild fruit juice contains many kinds of element. The amounts of each element differ with the growing location of the fruit. The elements found are: large amounts of potassium ( > 1000 mg l- ‘), phosphorus. calcium. magnesium, manganeseand zinc ( lOO- 1000 mg 1 ‘); small amounts of iron and sodium (lo- 100 mg 1- ‘). aluminum, chromium and cobalt (1- 10 mg 1 ‘); trace amounts of cadmium copper, lead. nickel, silicon. strontium and selenium ( < 1 mg 1 ‘). An appropriate matrix modifier was sought for suppressing the interferences of comparatively large amounts of potassium, phosphorus, calcium. magnesium, zinc and iron. Although platinum as a matrix modifier can decrease the overcompensation effect caused by phosphorus and iron, the analytical sensitivity is significantly affected, and therefore a modifier to increase the analytical sensitivity, such as nickel. copper or magnesium, is thought to be preferable to use with platinum for compensating the nega-

tive effect of platinum. Palladiumjmagnesium, proposed by Welz [17] as a universal matrix modifier was also tested. Accordingly, the following five matrix modifiers were selected to study the suppression of the interferences of the seven co-existing elements mentioned above: nickelcopper. palladium/magnesium, platinum/magnesium. platinum/nickel and platinum/copper. The results, shown in Table 2, indicate that phosphorus has the severest interference effect and only a platinum/nickel modifier among these five modifiers could suppress all interferences from the seven co-existing elements. Using platinum/nickel as a matrix modifier the analytical results obtained for a real juice sample by application of a standard calibration technique are the same as that obtained by application of the analyte addition technique. This demonstrates that a platinum/nickel matrix modifier also has the ability to suppress the interferences of the remaining co-existing elements (aluminum, cadmium, chromium, cobalt, copper, lead, silicon, sodium and strontium).

The suppression effects of different composi tions of a platinum/nickel matrix modifier on potassium. phosphorus and calcium were studied. The results, shown in Table 3, indicate that a matrix modifier composed from 10 /cg of platinum and 200 Llg of nickel has the best performance.

Table 4 Determination of selenium m three Lantingguo of platinumflnickel as a matrix modifier Sample number

L-l L-w L-i

.4mount

of Ni (jig)

Amount

K

P

Ca

100 100 100 100 100

IO IO IO IO 5

IO 25 5 IO 10

[4] [5] [6]

300 200 100 200 I50

IO IO 30 5 IO

Added (mg I-‘)

Found (mg I-‘)

Recovery (%)

0.70 0.20 0.20

0.22 0.71 0. I9

II0 105 95

of selenium

in Ic?ild fruit

juice

References

of a platinum

Permissible amoung (j(g) -

test

The proposed method was applied to the determination of selenium in three juices made from Lantingguo grown in different places. The results shown in Table 4, demonstrate that the proposed method could be used for the determination of selenium in such a wild fruit juice without preseparation of the matrix. The relative standard deviation was 14% for 0.20 mg 1-I of selenium (H = 8; 0.17. 0.22. 0.20, 0.25, 0.20, 0.18, 0.18 and 0.16 mg I ‘), A characteristic mass was 28 pg. The linear range of the calibration curve was O-60 ,~cg1 ’ and its correlation coefficient was 0.9998.

[3] of Pt (i(g)

Recovery

by use

of eight determinations. of three determinattona.

3.3. Detertninutiotz

[?I compositions

0.20” l).Xh O.I(Jb

’ Mean h Mean

[l] Table 3 Suppression effects of ditrerent nickel matrix modifier

Value obtained (mg I ‘)

juices

[7] [8] [9]

Perkin-Elmer Model HGA 500 Operation Manual. Perkin-Elmer Co.. 1982. J. Dedina. W. Frech. A. Cedergren, I. Lindberg and E. Lundberg. J. Anal. At. Spectrom.. 3 (1987) 435. M.S. Droessler and J-4. Holocombe. Can. J. Spectrosc., 31 (1986) 6. 0. Kujirai. T. Kobayashi. K. Ide and E. Sudo, Talanta. 30 (1983) 9. J. Kumpulainen, A.-M. Raittila. J. Lehto and P. Koivistoinern. J. Assoc. Off. Anal. Chem.. 66 (1983) 1129. B.E. Jacobson and G. Lockitch. Clin. Chem. (WinstonSalem. NC). 34 (1989) 709. L. Ping. K. Fuw~a and K. Matsumoto. Anal. Chim. Acta. I71 (1985) 279. C. Charlot, D. Rieu and J. Touati. Analusis, I7 (1989) 271. J. Alexander. K. Saeed and Y. Thomassen. Anal. Chim. Acta, I20 (1980) 377.

(IO]

G. Norheim, 4 (198.3)

K. Saeed

[I I] B. Sampson. [I?] P.L.H. Jonett [I31

and

Y. Thom;~arn.

1243. B. Welz. M. Anal. Chem..

Melcher and G. 316 (1983) 271.

A.G. Krynitsky. E. .Aradiand.

[16]

Thomasen. Fresenius’ Z. Anal. M.B. Knowles and K.G. Brodie.

[I71

Spectrocc..

J. Anal. At. Spectrom.. 2 (19X7) and M.I. Banton. Anal. Lett..

[I41 [I51

3 (10X8) B. Welz. Spectrom..

AI.

[IX]

99.

Schlemmer.

437. IY (19X61

Fresrnius‘

Anal. Chem.. 59 (1987) 1884. J. Aaseth. B. Radzich. K. Saeed

51 I. G. Schlemmer and 4 (1989) 305.

J.R.

Z.

and

Mudakail.

J. Anal.

At

Ashlno.

K.

Takada

(1994)

443.

and

K.

297

[19] [30]

E.H. C.K.

Larsen Martin

and and

J. Ekelund. J.C. Williams.

[II]

(1989) 691. D.L. Taalr\.

T.S.

Dimitrob

Hlrokawa.

Anal.

Chim.

.Analyst. 16 (1988) 97. J. Anal. At. Spectrom..

and

P.B.

[37]

At. Spectrom.. 5 11990) 189. J.E. Teagua-Nishimura. T. Tominaga. Matcumoto. Anal. Chem., 59 (I 987)

[23] [24]

K. Saeed. K. Saeed

[25]

(19X1) 381. J. Bauslaugh. Anal. Chim.

‘r.

Chem., 32X (1987) 367. J. Anal. .At. Spectrom..

T. Acta.

J. Anal. At. Spcctrom., and Y. Thomassen.

Mandjukov.

J. Anal.

T. Katsura 1637.

and

2 (1987) 151. Anal. Chim. Acta.

B. Radziuk. K. Saced Acta. I65 (IY84) 149.

and

4

Y. Thomassrn.

K.

130