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Determination of zinc in plant materials using ion-exchange chromatography
ANALYTICA
354
CIiiMICA
ACTA
VOL.
DETERMINATION OF ZINC IN PLANT MATERIALS ION-EXCHANGE CHROMATOGRAPHY*
19 {xg58~
USING
bY
Ilepavtrrre~~l of A gricullurul
Clwnlslry
und Soits, Universdy
(I/ Arzzonu,
Tzrcsorr,
Avis.
(U.S
A
.)
‘fhc must reliable method for the cleternlin~tioil of zinc in plant materials has been l’hat method usually requires three differen\. separation the dithizone procedurcl. and extraction steps to eliminate other ions which intcrfcrc in the zinc clctcrmination. ‘1’1~~ steps arc not only time-consuming but may result in the loss of zinc or contamination of the solution by zinc and other intcrfcring elcmcnts, It usually is possible to complete approximately 24 analysts in one day using the dithkonc procedure. Another disadvantage to the dithizone method is the USC of carbon tctrachloridc to extract the ~iIlc-clitl~i~one complex. Wflcrc ;Llarge number of analyses are to be pcrformcd this organic extractant may crcntc a health hazard due to its toxic fumes. Rusrr +\sIJ YOC~ have clescribecl a new reagent for zinc, namely ; Zincon (2-carboxy2’-llyclrosy-5’-sulfoforn~azylbcnzenc). They have rccorclcd some of the essential analytical properties of the zinc-zincon complex, and have given a method for the determination of zinc. A large number of other clcmcnts interfere in the zinc clctcrmination. Many of these clcments such as calcium, magnesium, manganese, iron, and copper commonly occur in plant mntcrials. The USCof ion-c,uchangc cl~roniatogral~l~y for the separation of certain ciemcnts is becoming more wiclcsprcad. Klcilus AND hIooHE3 using the anion exchanger Dowex r-S8 were successful in separating nickel, mangancsc, cobalt, copper, iron, and zinc. A similar teclmicluc has been described by JENTZSCII AND ~?I~OTSCII~~~. A mcthocl” proposccl for the clctcrminlrtion of zinc in plant materials by the use of Zincon, after separation of interfering metals by ion-exchange, has given erratic results in this laboratory. This may bc clue to the interference of ammonium ion from the buffer**, incomplete rcplaccmcnt of the adsorbed zinc by the use of the prescribed volume of o,oogN hydrochloric acid, ancl the lcakagc of iron(III) into the zinc eluate. ‘I’hc following proposed method climinutes the problems mentioned above and lends itself very satisfactorily for the routine und accurate determination of microgram quantities of zinc in the plant materials.
.-\I1 trnnstnItt;~~Khi
Lid i&lXWr~tlOl~ ” spcctroplrotolllctcr. A Uccltman
;P,lY Pyrex brand glnsswarc ---.-* Arizona Agr. Expt. Sta ** Unpubhshcd data. References
p.
359
were I)crforrncd 011it YilUSCh and Lomb “Spcctronlc plr mctcr, Model N-I was usccl for the pH measurcmentu, was usctl throughout the procedure. Tech
spectra
Papar
No. 440.
VOL.
19 (1958)
DETER;MINATIOS
OX:
%n
IX
PLANT
MATERIALS
355
The Ion-exchange columns wcrc constructed as follows. A short plecc of glass tubing (50 mm In length) was affixed to the bottom of a test tube having a Icngth of 150 mm and an lnslde dlametcr of 13 mm. A short p~ccc of plastic tubing and a clamp, or mom preferably a glass stopcock was placed at the end of the glass tube. A small plug of glass wool was placed in the bottom of the test tube to prcvcnt the exchange resin from moving through the tubing. A slurry of Dowcx 1-58, 50- IOO mesh was prepared usln~ IN sodium hyclros~clc The column was filled approxlmatcly half with dclonl/.ctl water and the slurry wab then introduced Into the column. The liquid was permitted to flow from the column, thcrcby aiding the bctthng of the resin. At no time was the liquid permitted to fall below the SLirfaCC of the r&n This proccdurc was continued until a column of rcbin 70 mm high was obtained. l’hc resin contained small amounts of zinc as a contaminant and thcrcforc was washed further with 100 ml of rN sodium hydroxiilc. The column was then trcatcd with 50 ml of ZN hytlrochlorlc acid. The resin was then ready for use A series of tight columns wcrc constructed, the flow rates ranging from I -3 ml/m~n A CLAHK ASD Lues buffer system of pir 9 o was uscde. A ICIp.p.m. standard solution of zinc was made using zinc metal dissolved in a small amount of coiiccntrated hytlrochloric acid. The Zincon reagent was prepared by dissolving o. 130 g of the reagent in 2 ml of IA’ sodium hydroxide and diluting to 100 ml with dcionizcd water. All other reagents and solutions wcrc prcparcd using analytical or reagent grade chemicals. All water used was deionized by passage through a combined cation and anion exchange system.
Wclgh a x-g sample of plant material, containing less than 50 y Zn, intc) a 50-ml bcakcr and place in a muffle furnace Ury-ash tlic haiiiplc at a tcmpcraturc of 475-500” for ,1pprosimately I 11. After the beaker has cooled, udd j nil conccntratcd nitric acid. 5 ml water, and 2 ml 70-72”//0 perchloric acid in the a\~ovc or&r and place the hcakcr 011 il h(Jtl~hLtC ov’or imxliiliii heat for I II. Then raise the heat and permit the mlxturc to go to drynes?r. If unoxidized organic mrttcrlal renlaIns after the beginning stages of the high heat trcatmciit, rcmuvc the beaker fruni ttic hutplatc, coul, and repeat the acid trcatinciit. To the oxidized plant ash aclcl IO in1 ZN hydr~JChhrlC acid and bring the rcsiduc into suIution. Filter the mixture through Whatman N~J. 40 paper and wash the flltcr with thrcu 5-11~1portions
of zN hydrochloric acid h wooden filter rack may bc attached above the ion-cxchangc columns with the filter stems placed inside the top of the ion-cxchangc tube. In thir manner the filtrate goes directly mto the column and not into a scparutc hcakcr, thcrcby possibly reducing loss or contamlnation through transference. If dcsmrrblc, a bcalccr can be urcd tu catch the flltratc. Introduce the flltratc, containing less than 50 y Zn, into the ran-cxchangc column. I
To further test the reinovril of interfering ions and the cluantitative replacement of adsorbed zinc a number of experiments were conducted. Previously it was noted” that up to 500 y of iron(II1) may be removed by an ion-exchange techniclue. To further clarify this point synthetic solutions containing iron(II1) and zinc were pre-
References Q. 359
356
R.
1.1. MAIER,
J. S. BULLOCK
TAULE REMOVAL
OF
INTEHPJ~RINC
IONS
--_-___ Ion
pldsellt
IOS
ISXCHANGE
COLU.M.Nb __-
.-_--%tr fwcse?d
-..--
(yJ
-.-.
200
30
Fe+”
600
30 0
28.9
pe+3
Ho0
30.0
12
&yt”
Go0
30
30.0’
Fe+”
600
30 0
30.01’
Fc+~
Go0
30.0
30 0‘
RlniJ
200
30 0
29.8
Mn+4
Ho0
30 0
30 4
Cu+l
100
30 0
3’ 0
50
30 0
30 5
Cu+~
30
30.0
31.0
cu+a
30
20
Cu”2
30
0
0
0
10.0
__ .__-
_-_
ZnlounJ(W
------
L’e+3
C”+”
.._-
________
29.7
0
19.6 II.0 _I--..
sodium .sulfitc xddctl prior tu transfcrcncc to column. b 15 ml 5% hyclroxylnminc hydrochloride ad&xl prior to transfcrcncc C rg ml x04, sorlium arscnitc ilddcd prior to transference to column
n
20
ml
19 (x958)
I BY
-.(y)
VOL.
_
I’%,
to column
pared and analyzed in the manner clescribccl above. As shown in Table I, amounts of iron in excess of Goo y interfere in the subsequent determination of zinc as all the iron is not replaced by o.gN hydrochloric acid but appears in the IN sodium hydroxide eluate. Small amounts of iron seriously affect the development and/or stability of the zinc -2incon complex. The addition of certain reducing agents may increase the upper limit of iron that can be tolerated (Table I). The difference in adsorption and replacement of the chlorocomplexes of iron and iron(II1) arc large enough4 that a conversion to the iron(I1) state might aid the separation of iron from zinc. Other methods to increase the amount of iron separated from zinc include decreasing the particle size of the resin and/or decreasing the flow rate of the columns *. Since the proposed method recommends using a r-g plant sample, it is doubtful that quantities of iron in the interfering range will be found. KESULTS
The quantitative recovery of zinc from the exchange column is satisfactory (Table II) and as shown in Table III, the accuracy of the proposed method compares favorably with the official A.O.A.C. method r. The proposed procedure is more rapid than the dithizone method. * Unpublished References
9. 359
data.
UETERBIINATIOR OF &I IN i=LANT MATERIALS
VOL. 19 (1958)
TABLE RECOVERY
ZINC
FROM
EXCHASGE
COLUMNS
Ztnc prcrml (y)
Z&HC /oun.d(y)
10.0 IO 0
10.0
30.0
40.0
29.7
IO.2
20.0
20.2
GO.0
1954 30.5
50.0 50.0
37.4 47.0 48.5
_20.0
30.0 --
38.2
__-
TABLE COblPARlSON
II
ION
Zinc /wnd (y.J
presrPlr (y)
ZlW
OF
OF
357
T1iE
PROPOSED
METHOD ZISC _.-____
ASD IN
--.
III A.O.A.C.
THE PtAST
blISTHOD
FOR
----_-.
Propo,nl (p pm. ._.-__-
__.___ ---_.-_
melhal Zn)
_.--__-
15.2
15.0
Peach
leaves
14 3
‘5.3
lJccim leavcv
21.5
22.8
Grnpefrult
12.9
13.8
Grape lcavcs
44.4
44. ’
Lcttucc
27.0
29.4
lcavcs
Icavcs --
steins
---.
OF
- _
lcnvcs
Cantaloupe
DETPHhllNATIOS
.A 0.A .C. nufhd [p p.m. Zu)
hxlc11
._ -__
THE
.MATERIALS
SIlt@k -___-.-.--
-
40.0
40.2
-
------_
To further test the reliability of the proposed method. a recovery investigation was conducted. Known amounts of zinc were added to particular plant samples whose zinc concentration was determined previously by the proposed method. These samples were ashed and analyzed as described in the above procedure. The recovery values are shown in Table IV. As a further check on the proposed method, a synthetic ash solution was prepared containing many of the elements found in plant materials. Known amounts of zinc were added to ro-ml portions of the ash solution and analyzed as described. The results are shown in Table V. DISCUSSION
The use of IN sodium hydroxide was satisfactory for replacing the exchangeradsorbed zinc. This eliminates the need for a controlled normality of hydrochloric acid to replace the zinc. The adsorption of cadmium- and lead-chloro complexes on an anion exchanger has been noted 4. The normality of hydrochloric acid required to replace the cadmium and lead was found to be less than that required for zinc and therefore the cadmium and lead may appear in the sodium hydroxide fraction. KALLMAN et al. 7 observed that by using a mixture of sodium hydroxide and sodium chloride they were able to replace zinc and lead from Dowex r-X8 but cadmium remained on the column.
*
Refwemss
p. 359
R. Ii. XAIER,
358
J. S. i3ULLOCK
TABLE RIXOVEHY
OF
ZINC
ADDED
-~__
TO
IV SELECTED
PLANT
SAMPLES
--_-
_ ___-.
I
21.5
0.0
2
210
42.5
20.0 0.0
2 1.0
10.0
29.7
8.7
0.0 10.0
25.0 34.6
9.6
0.0 20.0
15.0 34.6
0.0 30.0
37.0
26.9
10.0
37.0 45.6
8.6
0.0 10.0
15.0 25.7
10.7
3 4 5 6
TABLE OF
ZINC
19x3
10.0
0.0
7
D&TERMINATION
VOL. 19 (1958)
1N
V SYNTHETIC
ASH
SOLUTION -
zwc
presort (Y)
IO
ml ash solutiona
IO
ml
z,ttc --
/ound (VI
10.0
9.3
30.0
30.1
IO ml ash solution
40 .o
37.4
x0 ml ash solution
50.0
47.0
ash solution
a IO ml of nsh solution contains 30 mg I<+ 6 rug POo-3 Go mg Ca+’ 2.5 mg NI+~ 20 mg Mg+l 0.5 mg Fc+~ IO mg Na+
-_
--.
-.-
the followmg: 0.x mg Mn+J 0.1 mg A1+3 0 025 mg Co+’ 0.005 mg Mo+~
It is extremely unlikely that any appreciable amounts of lead and cadmium would be found in plant tissue. KEATON found no lead in the tops and roots of barley growing on a soil which did not receive applications of lead. However, it appeared advisable to study the influence of lead on the development of the zinc-zincon complex. In amounts up to roe y, lead did not interfere in the determination of zinc with zincon. JACKSON AND 13~0~~6 used IN hydrochloric acid to remove interfering ions from Dowex r-X8 prior to the removal of zinc. However, KRAUS AND MOORER used 0.5N hydrochloric acid to remove iron(II1). Results in this laboratory show that 0.5N hydrochloric acid was superior to IN hydrochloric acid in removing relatively large amounts of interfering elements, particularly iron(II1). References
p. 359
VOL.
19
(1g$3)
DETERMINATION
OF %l
IN
PLANT
MATERIALS
359
The proposed method is accurate and rapid for the determination of zinc in plant materials. For the routine analysis of a large number of samples, the procedure could he made more rapid by possibly altering the strength and volume of the IX sodium bydroxide solution so that the addition of 5 ml of the buffer would bring the solution to PH 9.0 without further adjustment. ACKSOWLEDGEMEST
Thanks supplying
arc due Mr. GLENN E. PRIELIPP of the Dow Chemical Company, cxperlmental samples of Dowcx x-X8 resin
Midland,
Mlchlgan,
for
SU,\IhIARY The objcctlve of this lnvcstlgatlou ww to devclop a rapld and accurate mcthocl for the dctcrmltratlon of zmc in plant matcnals. An Ion-cxchangc separation tcchmque to chminatc intcrfcrcnces in the Zmcon procedure for zinc IS dcscribcd. Comparison with the A O.A.C. method and cvaluatlon of zinc rccovcry studies show the proposed methotl to bc satisfactory for the analysis of mwzzrogram amounts of zinc in plant materlab. REFERENCES 1 Assoc.
OPPIC. AGH ~HEMISTS.~/ftC1R~n'fEfhOdSof~~tluiys~~.8tlicd.,~~~~hl~~gton. 1g55.p. i~o-1x2. AND J. l-1. Yore, /I~al. C/rent., 26 (x954) x3.+5. K. A. KRAUS ASD G. E. MOOHZ, J. Awl. C&m. Sot., 75 (x953) 14Go D. JENTXSCH ANI) 1. FROTSCHER, %. unaf Chenr., ‘44 (1955) 17. I<. K. JACKSON AND J. G. IJ~ow.u, Proc. :Iwt Sot. Horf. Set., 68 (1956) I. I. M. KOLTHOFP ASD 1-i.A. LAITISES, pff and 13ectro T~l~ufzons, 2nd cd., John Wiley and Sons, New York, 1948. p. 35. S. KALL%w, C. G. STEELE AND N. Y. CHU. Anal. Chew., 28 [x956) 230. C. M. KEATOS, Sozl Sea., 43 (x937) 410.
1 R.
9 4 6 0 7 @
AM. RUSH
Received
February
25th,
1958
354
CIiiMICA
ACTA
VOL.
DETERMINATION OF ZINC IN PLANT MATERIALS ION-EXCHANGE CHROMATOGRAPHY*
19 {xg58~
USING
bY
Ilepavtrrre~~l of A gricullurul
Clwnlslry
und Soits, Universdy
(I/ Arzzonu,
Tzrcsorr,
Avis.
(U.S
A
.)
‘fhc must reliable method for the cleternlin~tioil of zinc in plant materials has been l’hat method usually requires three differen\. separation the dithizone procedurcl. and extraction steps to eliminate other ions which intcrfcrc in the zinc clctcrmination. ‘1’1~~ steps arc not only time-consuming but may result in the loss of zinc or contamination of the solution by zinc and other intcrfcring elcmcnts, It usually is possible to complete approximately 24 analysts in one day using the dithkonc procedure. Another disadvantage to the dithizone method is the USC of carbon tctrachloridc to extract the ~iIlc-clitl~i~one complex. Wflcrc ;Llarge number of analyses are to be pcrformcd this organic extractant may crcntc a health hazard due to its toxic fumes. Rusrr +\sIJ YOC~ have clescribecl a new reagent for zinc, namely ; Zincon (2-carboxy2’-llyclrosy-5’-sulfoforn~azylbcnzenc). They have rccorclcd some of the essential analytical properties of the zinc-zincon complex, and have given a method for the determination of zinc. A large number of other clcmcnts interfere in the zinc clctcrmination. Many of these clcments such as calcium, magnesium, manganese, iron, and copper commonly occur in plant mntcrials. The USCof ion-c,uchangc cl~roniatogral~l~y for the separation of certain ciemcnts is becoming more wiclcsprcad. Klcilus AND hIooHE3 using the anion exchanger Dowex r-S8 were successful in separating nickel, mangancsc, cobalt, copper, iron, and zinc. A similar teclmicluc has been described by JENTZSCII AND ~?I~OTSCII~~~. A mcthocl” proposccl for the clctcrminlrtion of zinc in plant materials by the use of Zincon, after separation of interfering metals by ion-exchange, has given erratic results in this laboratory. This may bc clue to the interference of ammonium ion from the buffer**, incomplete rcplaccmcnt of the adsorbed zinc by the use of the prescribed volume of o,oogN hydrochloric acid, ancl the lcakagc of iron(III) into the zinc eluate. ‘I’hc following proposed method climinutes the problems mentioned above and lends itself very satisfactorily for the routine und accurate determination of microgram quantities of zinc in the plant materials.
.-\I1 trnnstnItt;~~Khi
Lid i&lXWr~tlOl~ ” spcctroplrotolllctcr. A Uccltman
;P,lY Pyrex brand glnsswarc ---.-* Arizona Agr. Expt. Sta ** Unpubhshcd data. References
p.
359
were I)crforrncd 011it YilUSCh and Lomb “Spcctronlc plr mctcr, Model N-I was usccl for the pH measurcmentu, was usctl throughout the procedure. Tech
spectra
Papar
No. 440.
VOL.
19 (1958)
DETER;MINATIOS
OX:
%n
IX
PLANT
MATERIALS
355
The Ion-exchange columns wcrc constructed as follows. A short plecc of glass tubing (50 mm In length) was affixed to the bottom of a test tube having a Icngth of 150 mm and an lnslde dlametcr of 13 mm. A short p~ccc of plastic tubing and a clamp, or mom preferably a glass stopcock was placed at the end of the glass tube. A small plug of glass wool was placed in the bottom of the test tube to prcvcnt the exchange resin from moving through the tubing. A slurry of Dowcx 1-58, 50- IOO mesh was prepared usln~ IN sodium hyclros~clc The column was filled approxlmatcly half with dclonl/.ctl water and the slurry wab then introduced Into the column. The liquid was permitted to flow from the column, thcrcby aiding the bctthng of the resin. At no time was the liquid permitted to fall below the SLirfaCC of the r&n This proccdurc was continued until a column of rcbin 70 mm high was obtained. l’hc resin contained small amounts of zinc as a contaminant and thcrcforc was washed further with 100 ml of rN sodium hydroxiilc. The column was then trcatcd with 50 ml of ZN hytlrochlorlc acid. The resin was then ready for use A series of tight columns wcrc constructed, the flow rates ranging from I -3 ml/m~n A CLAHK ASD Lues buffer system of pir 9 o was uscde. A ICIp.p.m. standard solution of zinc was made using zinc metal dissolved in a small amount of coiiccntrated hytlrochloric acid. The Zincon reagent was prepared by dissolving o. 130 g of the reagent in 2 ml of IA’ sodium hydroxide and diluting to 100 ml with dcionizcd water. All other reagents and solutions wcrc prcparcd using analytical or reagent grade chemicals. All water used was deionized by passage through a combined cation and anion exchange system.
Wclgh a x-g sample of plant material, containing less than 50 y Zn, intc) a 50-ml bcakcr and place in a muffle furnace Ury-ash tlic haiiiplc at a tcmpcraturc of 475-500” for ,1pprosimately I 11. After the beaker has cooled, udd j nil conccntratcd nitric acid. 5 ml water, and 2 ml 70-72”//0 perchloric acid in the a\~ovc or&r and place the hcakcr 011 il h(Jtl~hLtC ov’or imxliiliii heat for I II. Then raise the heat and permit the mlxturc to go to drynes?r. If unoxidized organic mrttcrlal renlaIns after the beginning stages of the high heat trcatmciit, rcmuvc the beaker fruni ttic hutplatc, coul, and repeat the acid trcatinciit. To the oxidized plant ash aclcl IO in1 ZN hydr~JChhrlC acid and bring the rcsiduc into suIution. Filter the mixture through Whatman N~J. 40 paper and wash the flltcr with thrcu 5-11~1portions
of zN hydrochloric acid h wooden filter rack may bc attached above the ion-cxchangc columns with the filter stems placed inside the top of the ion-cxchangc tube. In thir manner the filtrate goes directly mto the column and not into a scparutc hcakcr, thcrcby possibly reducing loss or contamlnation through transference. If dcsmrrblc, a bcalccr can be urcd tu catch the flltratc. Introduce the flltratc, containing less than 50 y Zn, into the ran-cxchangc column. I
To further test the reinovril of interfering ions and the cluantitative replacement of adsorbed zinc a number of experiments were conducted. Previously it was noted” that up to 500 y of iron(II1) may be removed by an ion-exchange techniclue. To further clarify this point synthetic solutions containing iron(II1) and zinc were pre-
References Q. 359
356
R.
1.1. MAIER,
J. S. BULLOCK
TAULE REMOVAL
OF
INTEHPJ~RINC
IONS
--_-___ Ion
pldsellt
IOS
ISXCHANGE
COLU.M.Nb __-
.-_--%tr fwcse?d
-..--
(yJ
-.-.
200
30
Fe+”
600
30 0
28.9
pe+3
Ho0
30.0
12
&yt”
Go0
30
30.0’
Fe+”
600
30 0
30.01’
Fc+~
Go0
30.0
30 0‘
RlniJ
200
30 0
29.8
Mn+4
Ho0
30 0
30 4
Cu+l
100
30 0
3’ 0
50
30 0
30 5
Cu+~
30
30.0
31.0
cu+a
30
20
Cu”2
30
0
0
0
10.0
__ .__-
_-_
ZnlounJ(W
------
L’e+3
C”+”
.._-
________
29.7
0
19.6 II.0 _I--..
sodium .sulfitc xddctl prior tu transfcrcncc to column. b 15 ml 5% hyclroxylnminc hydrochloride ad&xl prior to transfcrcncc C rg ml x04, sorlium arscnitc ilddcd prior to transference to column
n
20
ml
19 (x958)
I BY
-.(y)
VOL.
_
I’%,
to column
pared and analyzed in the manner clescribccl above. As shown in Table I, amounts of iron in excess of Goo y interfere in the subsequent determination of zinc as all the iron is not replaced by o.gN hydrochloric acid but appears in the IN sodium hydroxide eluate. Small amounts of iron seriously affect the development and/or stability of the zinc -2incon complex. The addition of certain reducing agents may increase the upper limit of iron that can be tolerated (Table I). The difference in adsorption and replacement of the chlorocomplexes of iron and iron(II1) arc large enough4 that a conversion to the iron(I1) state might aid the separation of iron from zinc. Other methods to increase the amount of iron separated from zinc include decreasing the particle size of the resin and/or decreasing the flow rate of the columns *. Since the proposed method recommends using a r-g plant sample, it is doubtful that quantities of iron in the interfering range will be found. KESULTS
The quantitative recovery of zinc from the exchange column is satisfactory (Table II) and as shown in Table III, the accuracy of the proposed method compares favorably with the official A.O.A.C. method r. The proposed procedure is more rapid than the dithizone method. * Unpublished References
9. 359
data.
UETERBIINATIOR OF &I IN i=LANT MATERIALS
VOL. 19 (1958)
TABLE RECOVERY
ZINC
FROM
EXCHASGE
COLUMNS
Ztnc prcrml (y)
Z&HC /oun.d(y)
10.0 IO 0
10.0
30.0
40.0
29.7
IO.2
20.0
20.2
GO.0
1954 30.5
50.0 50.0
37.4 47.0 48.5
_20.0
30.0 --
38.2
__-
TABLE COblPARlSON
II
ION
Zinc /wnd (y.J
presrPlr (y)
ZlW
OF
OF
357
T1iE
PROPOSED
METHOD ZISC _.-____
ASD IN
--.
III A.O.A.C.
THE PtAST
blISTHOD
FOR
----_-.
Propo,nl (p pm. ._.-__-
__.___ ---_.-_
melhal Zn)
_.--__-
15.2
15.0
Peach
leaves
14 3
‘5.3
lJccim leavcv
21.5
22.8
Grnpefrult
12.9
13.8
Grape lcavcs
44.4
44. ’
Lcttucc
27.0
29.4
lcavcs
Icavcs --
steins
---.
OF
- _
lcnvcs
Cantaloupe
DETPHhllNATIOS
.A 0.A .C. nufhd [p p.m. Zu)
hxlc11
._ -__
THE
.MATERIALS
SIlt@k -___-.-.--
-
40.0
40.2
-
------_
To further test the reliability of the proposed method. a recovery investigation was conducted. Known amounts of zinc were added to particular plant samples whose zinc concentration was determined previously by the proposed method. These samples were ashed and analyzed as described in the above procedure. The recovery values are shown in Table IV. As a further check on the proposed method, a synthetic ash solution was prepared containing many of the elements found in plant materials. Known amounts of zinc were added to ro-ml portions of the ash solution and analyzed as described. The results are shown in Table V. DISCUSSION
The use of IN sodium hydroxide was satisfactory for replacing the exchangeradsorbed zinc. This eliminates the need for a controlled normality of hydrochloric acid to replace the zinc. The adsorption of cadmium- and lead-chloro complexes on an anion exchanger has been noted 4. The normality of hydrochloric acid required to replace the cadmium and lead was found to be less than that required for zinc and therefore the cadmium and lead may appear in the sodium hydroxide fraction. KALLMAN et al. 7 observed that by using a mixture of sodium hydroxide and sodium chloride they were able to replace zinc and lead from Dowex r-X8 but cadmium remained on the column.
*
Refwemss
p. 359
R. Ii. XAIER,
358
J. S. i3ULLOCK
TABLE RIXOVEHY
OF
ZINC
ADDED
-~__
TO
IV SELECTED
PLANT
SAMPLES
--_-
_ ___-.
I
21.5
0.0
2
210
42.5
20.0 0.0
2 1.0
10.0
29.7
8.7
0.0 10.0
25.0 34.6
9.6
0.0 20.0
15.0 34.6
0.0 30.0
37.0
26.9
10.0
37.0 45.6
8.6
0.0 10.0
15.0 25.7
10.7
3 4 5 6
TABLE OF
ZINC
19x3
10.0
0.0
7
D&TERMINATION
VOL. 19 (1958)
1N
V SYNTHETIC
ASH
SOLUTION -
zwc
presort (Y)
IO
ml ash solutiona
IO
ml
z,ttc --
/ound (VI
10.0
9.3
30.0
30.1
IO ml ash solution
40 .o
37.4
x0 ml ash solution
50.0
47.0
ash solution
a IO ml of nsh solution contains 30 mg I<+ 6 rug POo-3 Go mg Ca+’ 2.5 mg NI+~ 20 mg Mg+l 0.5 mg Fc+~ IO mg Na+
-_
--.
-.-
the followmg: 0.x mg Mn+J 0.1 mg A1+3 0 025 mg Co+’ 0.005 mg Mo+~
It is extremely unlikely that any appreciable amounts of lead and cadmium would be found in plant tissue. KEATON found no lead in the tops and roots of barley growing on a soil which did not receive applications of lead. However, it appeared advisable to study the influence of lead on the development of the zinc-zincon complex. In amounts up to roe y, lead did not interfere in the determination of zinc with zincon. JACKSON AND 13~0~~6 used IN hydrochloric acid to remove interfering ions from Dowex r-X8 prior to the removal of zinc. However, KRAUS AND MOORER used 0.5N hydrochloric acid to remove iron(II1). Results in this laboratory show that 0.5N hydrochloric acid was superior to IN hydrochloric acid in removing relatively large amounts of interfering elements, particularly iron(II1). References
p. 359
VOL.
19
(1g$3)
DETERMINATION
OF %l
IN
PLANT
MATERIALS
359
The proposed method is accurate and rapid for the determination of zinc in plant materials. For the routine analysis of a large number of samples, the procedure could he made more rapid by possibly altering the strength and volume of the IX sodium bydroxide solution so that the addition of 5 ml of the buffer would bring the solution to PH 9.0 without further adjustment. ACKSOWLEDGEMEST
Thanks supplying
arc due Mr. GLENN E. PRIELIPP of the Dow Chemical Company, cxperlmental samples of Dowcx x-X8 resin
Midland,
Mlchlgan,
for
SU,\IhIARY The objcctlve of this lnvcstlgatlou ww to devclop a rapld and accurate mcthocl for the dctcrmltratlon of zmc in plant matcnals. An Ion-cxchangc separation tcchmque to chminatc intcrfcrcnces in the Zmcon procedure for zinc IS dcscribcd. Comparison with the A O.A.C. method and cvaluatlon of zinc rccovcry studies show the proposed methotl to bc satisfactory for the analysis of mwzzrogram amounts of zinc in plant materlab. REFERENCES 1 Assoc.
OPPIC. AGH ~HEMISTS.~/ftC1R~n'fEfhOdSof~~tluiys~~.8tlicd.,~~~~hl~~gton. 1g55.p. i~o-1x2. AND J. l-1. Yore, /I~al. C/rent., 26 (x954) x3.+5. K. A. KRAUS ASD G. E. MOOHZ, J. Awl. C&m. Sot., 75 (x953) 14Go D. JENTXSCH ANI) 1. FROTSCHER, %. unaf Chenr., ‘44 (1955) 17. I<. K. JACKSON AND J. G. IJ~ow.u, Proc. :Iwt Sot. Horf. Set., 68 (1956) I. I. M. KOLTHOFP ASD 1-i.A. LAITISES, pff and 13ectro T~l~ufzons, 2nd cd., John Wiley and Sons, New York, 1948. p. 35. S. KALL%w, C. G. STEELE AND N. Y. CHU. Anal. Chew., 28 [x956) 230. C. M. KEATOS, Sozl Sea., 43 (x937) 410.
1 R.
9 4 6 0 7 @
AM. RUSH
Received
February
25th,
1958