Determination of trace elements in pumpkin seed oils and pumpkin

seeds by ICP-AES

Iva Juranovic,a Patrick Breinhoelderb and Ilse Steffan*b

aDepartment of Analytical Chemistry, Faculty of Science, University of Zagreb,Strossmayerov trg 14, HR-10000 Zagreb, Croatia

bInstitute of Analytical Chemistry, University of Vienna, Waehringerstrasse 38, A-1090Vienna, Austria

Received 23rd September 2002, Accepted 28th November 2002

First published as an Advance Article on the web 11th December 2002

Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for the determination of the

elements present in pumpkin seed oil and pumpkin seeds. After extraction of the oil from pumpkin seeds a

residue was obtained. For the determination of elements three types of samples were used: oil, seeds and the

residue (after oil extraction). Three different digestion types were applied: open vessel and closed vessel

digestion in a steel bomb as well as microwave digestion in a closed system. For most elements of interest the

measured concentration differs depending on the digestion method used. After microwave digestion a good

reproducibility for ICP-AES measurements for all elements was found. Determination of Zn by ICP-AES is

possible both after open and closed vessel digestion (steel bomb or microwave digestion). No loss of volatile

compounds in pumpkin oil during preparation or microwave digestion prior to ICP-AES analysis could be

observed. In general, the recoveries for all elements in pumpkin seed oils and seeds were w95%, for S only

they were v50%. Differences in the element concentration were found for seed oil obtained from the same

seeds but prepared by two different procedures, extracted by Soxhlet and commercially produced after roasting

of the seeds. The differences of the measured element concentrations after application of different types of

dissolution procedures are discussed. The closed vessel dissolution was found to be the best procedure prior to

the ICP-AES determination of metals. The method is evaluated by application of the standard addition method

and by recovery experiments. Addition of salt during the oil production procedure causes approx. 10 times the

Ca, K, Mg, and Na amounts compared to the Soxhlet extracted oil produced in the laboratory. Higher amounts

of Na could be registered in the residues as well. The LODs were v0.1 mg g21 for Ca, Cd, Mg, Mn, Ti, and

Zn, in the range of 0.1 to 0.8 mg g21 for Co, Cu, Fe, K, Mo, Na, Ni, Pb, and V, and w0.8 mg g21 for Al, Cr

and P in pumpkin oil samples.

1. Introduction

The determination of trace elements in edible seed oils andseeds has gained more importance during the last few yearsbecause they contain naturally occurring antioxidants andessential elements. The content of metals and their species(chemical forms) in edible seed oils depends on several factors.The metals can be incorporated into the oil from the soil orbe introduced during the production process. The presence oftrace metals such as Cu, Fe, Mn, Ni, and Zn are known to havedifferent effects on the oxidative stability of edible seed oils.Lead and copper are potentially present in oils caused byenvironmental contamination.1–3

Hydrogenation of edible seed oils and fats has beenperformed using nickel catalysts. The presence of copper andiron can be caused by the processing equipment as well.Because of the metabolic functions of the metals, a develop-ment of fast and accurate analytical methods for trace elementdetermination in oils is important from the point of view ofboth quality control of production and food analysis. Theauthenticity of products is important from the standpoints ofboth commercial value and health aspects. Over the years, ahigh degree of sophistication has evolved for chromatographicmethods4–6 for the analysis of components of oils and fats.At the same time spectroscopic methods7–10 are emerging aspotential tools for a rapid screening of samples for thedetection of their adulteration. Inductively coupled plasmaatomic emission spectrometry (ICP-AES) and atomic absorp-tion spectrometry (AAS) are the most commonly used

techniques for the determination of metals in differentsamples.11,12 Fats and oils are particularly difficult to analyzefor their trace metal contents. Different digestion methods wereapplied for oil digestion prior to spectrometric measurements.Many of the used wet or dry digestion methods are notrecommended for use in high fat material because of the asso-ciated safety hazards.13 A direct determination method likedilution with an appropriate organic solvent followed by directaspiration into an atomic absorption flame or an ICP-excitation unit is sometimes not sensitive enough. In mostcases the analytical method exhibits changes in the excitationpower for organic media compared to aqueous solutions.14

Also calibration is more difficult in organic media.15,16

Optional methods of sample introduction into ICP-AES arethe emulsions-formation techniques. Their application doesnot require destruction of the organic matter or the use of largeamounts of organic solvent. Their disadvantage compared toaqueous systems is the difficulty occurring in calibration sinceaqueous standard solution cannot be used in this case. Thestability of emulsions, selection of the surfactant, the propor-tions of the phases, the preparation procedure, and the natureof the analyte compounds present in the matrix are usuallylimitations for such a method.8,17,18

Procedures based on trace element extraction by differentextractants are often time consuming and prone to losses andcontamination.19 An alternative methodology is microwave-enhanced dissolution chemistry. It enables fast, efficient andreproducible sample preparation. Sample solutions are heatedso effectively that the reaction time can be reduced drastically,

54 J. Anal. At. Spectrom., 2003, 18, 54–58 DOI: 10.1039/b209308c

This journal is # The Royal Society of Chemistry 2003

Dow

nloa

ded

on 0

2 O

ctob

er 2

012

Publ

ishe

d on

11

Dec

embe

r 20

02 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/B20

9308

CView Online / Journal Homepage / Table of Contents for this issue

often from days to minutes. Furthermore the level of thereaction and process control offered by microwave heating isbetter than by any other heating method.8,20

The aim of this work was the determination of elementsin pumpkin seed oil and seeds by ICP-AES. Furthermoredifferences in element concentrations between oil extracted bySoxhlet (self extracted) and commercially pressed pumpkinseed oil from roasted seeds should be registered. Self extractedoil was gained by Soxhlet extraction without salt additionduring the procedure. The resulting product was used forcomparison to commercially pressed pumpkin oil.

After the oil is extracted from pumpkin seeds a residue isobtained. The concentrations of the elements in oil, seeds andresidue were determined, applying three different digestiontypes: open vessel and closed vessel digestion in a steel bomb aswell as microwave digestion in a closed system.

2. Experimental

2.1. Chemicals and glassware

Nitric acid (p.A.), hydrogen peroxide (30% H2O, p.A.) andsingle element standards p.A. (Merck, Darmstadt, Germany)were used for the experimental work. Aqueous standardstock solutions were used after appropriate dilution. Oil andseed samples were commercially available. All glassware wascleaned with nitric acid prior to use.

2.2. Apparatus

For the element detection and determination an ARL 3580 ICPspectrometer (ARL, Ecublens, Switzerland) equipped with anHF-generator (Henry, 27.12 MHz) and RF power supply(1200 W) was used. The measurements were carried outusing the sequential Paschen–Runge part of the spectrometerequipped with a grating (1080 lines mm21), a Fassel typetorch and a computer (DEC 316 sx). The gas flows usedwere/L min21: outer gas/12, intermediate/0.8, aerosol carrier/1.Observation height was 15 mm above coil. All measurementswere performed with a Babington-type nebulizer (ARLMDSN). For microwave digestion of the samples a highperformance microwave digestion unit MLS-1200 MEGAequipped with an EM-30 unit (Milestone GmbH) was applied.

2.3. Sample preparation for ICP-AES

Samples of oils, seeds and residues were weighed and sub-sequently digested by three different procedures: open vesselwet digestion, closed vessel wet digestion under pressure in asteel bomb or using the microwave digestion unit. Afterdigestion with a mixture of nitric acid and hydrogen peroxideclear solutions were obtained and the analytes were determinedby ICP-AES.

Prior to the analysis of the elements by ICP-AES the oil wasextracted from the ground seeds using a Soxhlet apparatus(petroleum ether, bp 60–90 uC, 24 h). After extraction of theoil from the seeds a residue was left. For the determination ofthe elements three types of samples were used: oil, seeds andresidue.

For this purpose 1 g each of the oils, seeds and residues wereweighed for the open vessel digestion. Open vessel digestions ofthe samples were performed in glass vessels after addition of5 mL of HNO3 conc. and 15 drops of H2O2 at approx. 120 uCand heating of the samples for approximately 12 h. During thedigestion procedure the same amount of acid and hydrogenperoxide was added to the samples again twice. After digestionall the samples were transferred into 10 or 20 mL volumetricflasks and filled to volume. For each series of digestions areagent blank was prepared.

For the closed vessel digestion of the samples steel bombsequipped with a PTFE inlet were used. To 0.25 g oil, seeds or

residue 5 mL of HNO3 conc. and 15 drops of H2O2 wereadded and the sample was heated to 100 uC for approx. 12 h.After digestion all the samples were transferred into 10 mLvolumetric flasks and diluted to volume with 1 M HNO3 formeasurement.

For the microwave digestion procedure oil (0.5 g), seeds(0.5 g) and residue (0.5 g) were weighed into the digestionvessels. The digestions were performed by adding 4 mL ofHNO3 conc. and 2 mL H2O2 (30% v/v) to the sample. Themicrowave program applied is listed in Table 2 (see later). Arotating turntable was used to insure homogeneous distribu-tion of the microwave radiation in the oven. Temperaturecontrol required a temperature sensor in one vessel during theentire decomposition. The oil, seeds and residues were digestedaccording to the following optimized program (Power in W/time in min): 250/2, 0/1, 250/2, 600/1, 400/5, ventilation 3.0 min.The internal temperature was limited to 240 uC during thelast step and ventilation. After cooling all the digests weretransferred into 10 mL volumetric flasks and diluted to volumewith HNO3 (1% v/v). Reagent blanks were prepared similarlyto the samples.

The element content of commercially produced pumpkinseed oil (‘‘roasted seeds’’), self extracted oil (Soxhlet apparatus)and salad oil products available at local markets were usedfor comparison. In the laboratory the different oils wereextracted by a Soxhlet apparatus from ground seeds withoutaddition of salt.

2.4. Calibration procedure

The system was calibrated using aqueous mixed standards. Allcalibration curves were based on five different concentrations,including the blank. Standard solutions were prepared bydiluting a 1000 mg L21 multielement solution (ICP Multi-element Standard IV, Merck, Darmstadt, FRG). The con-centration ranges for the elements were: 5 to100 mg L21 of Al,Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, S, Ti, V, and Zn, and500 to 1000 mg L21 of Ca, K, Na, and P. Calibration rangeswere modified according to the expected concentration rangesof the elements of interest.

2.5. Spiking procedures

Standard additions were performed by addition of specificvolumes of aqueous standard solutions to the set of the samplesprepared. Sample spikes were prepared in triplicate (a, b and c).The oils were weighed, approx. 0.5 g, into digestion flasks forthe microwave digestion procedure and, approx. 0.25 g, forthe steel bomb. Standards were added (1 mL of standard c ~100 mg L21) and the samples were digested with a mixtureof nitric acid and hydrogen peroxide in the microwave oven ora steel bomb. After digestion the clear digests obtained weretransferred into 10 mL flasks and measured by ICP-AES.To pumpkin oil (p.oil 1) and pumpkin seeds (sample LSI4)10 mg L21 of Cd, Cu, Mo, Na, Ni, and Ti were added; topumpkin oil (sample LOI2) and pumpkin seeds (sample LSI5)10 mg L21 of Al, Ca, Co, Fe, P, and Zn, were added; topumpkin oil (sample LOI1) and pumpkin seeds (sample LSI5)10 mg L21 of Cr, K, Mg, Mn, Pb, S, and V were added. Afterdigestion the clear digests were transferred into 10 mL flasksand measured by ICP-AES. Furthermore the residues wereweighed (approx. 0.5 g) into digestion flasks for the microwavedigestion procedure and standards were added (1 mL ofstandard c ~ 100 mg L21). The samples were digested with amixture of nitric acid and hydrogen peroxide, transferredinto 10 mL flasks and measured by ICP-AES.

2.6. The limits of detection (LOD)

The limits of detection (LOD) were calculated according toBoumans15 using 3s. LODs were determined in pure element

J. Anal. At. Spectrom., 2003, 18, 54–58 55

Dow

nloa

ded

on 0

2 O

ctob

er 2

012

Publ

ishe

d on

11

Dec

embe

r 20

02 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/B20

9308

C

View Online

standards and in the pumpkin oil samples. The limits ofdetection were determined by measuring an appropriatereagent blank solution ten times and a standard solutionthree times. The detection limit was calculated as theconcentration equivalent to three times the standard deviationof the signal of the oil blank solution. All standard deviationsare based on measurements in triplicate.

2.7. ICP-AES determination

Prior to the sequential analysis line selection was performedfor every element (Table 1).

The background correction position was selected as10.14 nm. The integration time used was 5 s. For the deter-mination of K, Na, P, and S sequential spectral lines were used,while for the other elements a simultaneous program wasapplied.

3. Results and discussion

Table 2 shows the results obtained for all three digestionmethods for Al, Fe and Zn only. For the other elementsinvestigated the results varied drastically depending on thedigestion method used. Determination of Zn in pumpkin oils,seeds and residues by ICP-AES is possible both after open andclosed vessel digestion (steel bomb or microwave digestion).The differences of the results for Al and Fe obtained by usingopen and closed vessel methods varied significantly accordingto a t-test. Lower results up to approx. 50% were obtainedfor other elements after open vessel digestion compared to theclosed vessel digestion (steel bomb and microwave) methods.The differences between the results for both closed vesseldigestions are not statistically significant for most of theelements. This indicates that no loss by volatilization occurredin both cases. Comparison of the two closed vessel methodsof sample preparation, microwave digestion vs. steel bomb,results in the conclusion that microwave digestion is less timeconsuming. Further, more samples can be digested at the sametime. After the microwave digestion good reproducibility forICP-AES measurements for all elements was observed (approx.5% RSD), indicating that the microwave digestion of thesamples was complete. For testing of the losses of elementsoccurring during the laboratory procedure of oil production(evaporating of the solvent and complete removal of thesolvent using a vacuum pump) commercially producedpumpkin oil was also treated in the same way as the oilextracted in the laboratory. The microwave digestion ofcommercially produced pumpkin oils was performed byadding nitric acid and hydrogen peroxide to the samplesfollowed by ICP-AES determination of metals. No loss of theelements during preparation or microwave digestion prior tothe ICP-AES analysis could be noticed. The procedure isnot limited to non-volatile metals as can be seen from Table 3.According to the results it could be concluded that microwavedigestion is an appropriate technique for digestion of edibleoil samples.

In Table 4 the results obtained by the standard additionmethod and the recovery experiments for pumpkin oil (sample 2)are shown. The expected concentration of the elements was10 mg L21 (200 mg g21). In general, recoveries for all elementsin pumpkin oils were w95%. For Na and S they were v50%or 70%, respectively.

Results for spike experiments in pumpkin oil (sample 1) andpumpkin seeds (sample 1) are given in Table 5. The expectedconcentration of elements was 10 mg L21 (200 mg g21). Reco-veries for all elements in pumpkin oil and pumpkin seeds wereapprox. 10 mg L21, or w95%, except for S they were v50%.The results clearly demonstrate that this type of digestions andICP-measurements are suitable for all elements except S.

The limits of detection obtained for the determination of the

Table 2 Determination of Al, Fe and Zn in pumpkin oil (sample 1) andseeds (sample 1) after microwave digestion (mW), open vessel digestion(op) and digestion in steel bomb (sb). Results in mg g21

Pumpkinoil Al Fe Zn

Pumpkinseeds Al Fe Zn

Microwavedigestion

31.9 67.83 12.21 Microwavedigestion

69.86 139.13 59.64

Steel bomb 32.03 60.16 11.64 Steel bomb 72.66 151.08 53.15Open vessel 24.76 47.19 12.74 Open vessel 59.87 93.53 54.23

Table 1 Limits of detection and line selection for determination ofelements in pumpkin oil

Element LOD/mg g21 pumpkin oil Wavelength/nm

Al 0.920 396.1Ca 0.041 393.3Cd 0.044 226.5Co 0.356 239.8Cr 0.880 267.7Cu 0.293 327.3Fe 0.320 259.9K 0.248 766.5Mg 0.030 279.5Mn 0.032 257.6Mo 0.161 202.0Na 0.139 589.6Ni 0.164 341.4P 1.101 178.3Pb 0.166 220.3S — 181.0Ti 0.042 337.2V 0.114 310.2Zn 0.051 206.2

Table 3 Pumpkin oil A, B and Ca

Ca Cd Cr Cu Fe Mg Mo Na Ti V ZnAl, Co, Ni,Mn, P, K, Pb

A a 1.46 1.74 6.63 9.76 15.45 46.04 0.84 34.41 3.87 24.65 3.22 vDLb

A b 6.13 1.72 4.93 9.91 14.4 41.12 0.81 33.35 3.84 22.26 2.88 vDLb

B a 7.85 1.76 8.6 14.77 17.75 48.62 0.91 37.82 3.91 26.51 3.55 vDLb

B b 5.43 1.71 5.05 10.59 15.88 40.46 0.79 36.42 3.83 24.86 3.25 vDLb

C a 7.28 1.76 8.46 14.59 17.7 48.86 0.9 36.61 3.91 26.59 3.49 vDLb

C b 6.4 1.72 7.44 12.83 15.56 42.97 0.82 32.2 3.84 23.38 3.07 vDLb

Mean 5.8 1.7 6.8 12.1 16.1 44.7 0.8 35.1 3.9 24.7 3.2SD 2.30 0.02 1.61 2.30 1.34 3.70 0.05 2.20 0.04 1.71 0.25%RSD 39.4 1.1 23.5 19.0 8.3 8.3 5.9 6.2 1.0 6.9 7.7aA—commercially produced pumpkin oil. B—commercially produced pumpkin oil was diluted with petroleum ether and the solvent was evaporatedon a rotary evaporator at 45 uC. C—commercially produced pumpkin oil was filled in a round bottom flask, connected to a vacuum pump atroom temperature for 30 min. Results are given in mg g21. bThe LOD were 0.1 mg g21 for Co, K, Mn, Ni, Pb and w0.8 mg g21 for Al and P.

56 J. Anal. At. Spectrom., 2003, 18, 54–58

Dow

nloa

ded

on 0

2 O

ctob

er 2

012

Publ

ishe

d on

11

Dec

embe

r 20

02 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/B20

9308

C

View Online

elements in pumpkin oil are given in Table 1. LODs weredetermined also in pumpkin seeds and pumpkin oil residuesamples. The limits of detection for the elements in thosesamples were the same as for the elements in pumpkin oil(Table 1). Limits of detection v0.1 mg g21 were obtained forCa, Cd, Mg, Mn, Ti, and Zn. For Co, Cu, Fe, K, Mo, Na, Ni,Pb, and V they were in the range from 0.1 to 0.8 mg g21, and forAl, Cr, and P w0.8 mg g21.

Further improvements of the method’s performance, espe-cially for the S determination are limited by the sample amountand the reagent volumes, necessary for the digestion procedure.Smaller volumes of nitric acid and hydrogen peroxide did notlead to complete digestion. Higher volumes of reagents caneven cause excessive foaming and sample loss by the vapourremoval system.

The clear sample digests obtained by the method describedcan be used not only for ICP-AES but also for ICP-MS,graphite furnace or flame atomic absorption spectrometry.Compared to direct analysis of samples after dilution with anorganic solvent, the digestion method applied for this studyallows a simultaneous determination of metals and avoidslimitations due to the introduction of a carbonaceous matrix orcontamination caused by the organic solvents used. Figs. 1 and2 show results for the determination of elements in oil, seedsand residue after oil extraction and subsequent digestion usingthe microwave unit.

For all residues investigated the concentrations of the ele-ments of interest are higher compared to the ones measured forseeds and oils.

In all samples investigated the concentration of the toxicelements (Cd, Pb) was rather low; approx. 10 mg L21 or less forCd and Pb and approx. 6 mg L21 or less for Mo, Ni and Ti.

Salad pumpkin oil is commercially produced from roasted

seeds (PK is the so called ‘‘Presskuchen’’ i.e. molding cake).This type of oil was used also for comparison to the selfextracted oil (‘‘Soxhlet’’ apparatus). Higher concentrations ofCa, K, Mg, Na, and P in PK-oil samples were determinedcaused by addition of salt (NaCl) to the roasted seeds beforepressing of the oil. Salt is added to obtain a higher amount ofoil from the seeds. Self extracted oil contained approx. 10 timesless Ca, K, Mg, Na, and P than the commercially producedpumpkin oil from ‘‘roasted seeds’’. The amounts of Ca, K, Mg,Na, and P depend on the procedure of the oil production. Forroasted seeds: 70 to 90 mg Ca g21, 110 to 300 mg K g21, 150 to250 mg Mg g21, 190 to 440 mg Na g21, and 450 to 950 mg P g21

were measured. Furthermore the results of the elementdeterminations in the different residue samples were comparedto those obtained in oils. No significant differences of theelement concentrations were found for the residues after oilextraction by a Soxhlet apparatus and the residues afterpressing of the oil. With one exception: for Na a difference of23.78 to 31.04 mg Na g21 for residues of ground seeds toapprox. 10000 mg Na g21 for the residues after pressing of theoil was found. As expected adding salt to seeds before pressingof the oil causes an increase of the Na amount of the oil. Selfextracted oil was gained from ground seeds using a Soxhletapparatus (without adding salt). Adding salt in commerciallyproduced pumpkin seed oil causes high amounts of Ca, K, Mg,Na, and especially P.

4. Conclusion

For most elements of interest the concentrations in pumpkinoils, seeds and residues differ considerably depending on thedigestion method applied. Determination of Zn by ICP-AES ispossible both after open and closed vessel digestion (steel bombor microwave digestion). The microwave digestion is less time

Table 4 Results for spike and recovery experiments for pumpkin oil (sample 2) after microwave digestion. Results in mg L21

Al Ca Cd Co Cr Cu Fe K Mg Mn Mo Na Ni P Pb S Ti V Zn

p.oil 2a 9.3 10.0 9.6 9.2 9.5 9.3 10.0 10.6 10.6 10.0 9,7 3.4 9.2 9.2 10.2 6.6 13.1 9.8 9.2p.oil 2b 11.5 11.7 11.4 12.0 11.2 12.8 11.5 12.4 12.8 11.7 11.1 4.8 10.4 9.8 10.0 8.7 16.4 11.6 12.6p.oil 2c 10.3 10.6 10.3 10.0 10.1 10.4 10.5 9.9 11.7 10.6 10.1 4.8 9.6 13.0 9.1 7.2 15.1 10.6 13.0

Mean 10.4 10.8 10.4 10.4 10.2 10.8 10.7 11.0 11.7 10.8 10.3 4.4 9.7 10.7 9.8 7.5 14.9 10.7 11.6SD 1.1 0.9 0.9 1.4 0.9 1.8 0.8 1.3 1.1 0.9 0.7 0.8 0.6 2.0 0.6 1.1 1.7 0.9 2.1

Table 5 Results for spike experiments with pumpkin oil (sample 1) and pumpkin seeds (sample 1) after digestion in a steel bomb. Results in mg L21

Al Ca Cd Co Cr Cu Fe K Mg Mn Mo Na Ni P Pb S Ti V Zn

p. oil 1 1.6 0.7 10.6 2.9 1.7 9.2 3.5 2.1 0.9 0.3 9.3 11.1 11.0 5.9 0.2 0.0 13.9 0.0 0.7p. oil 2 10.9 10.9 0.5 13.9 1.6 0.0 9.5 1.3 0.8 0.2 0.1 1.0 0.0 13.7 0.1 0.0 0.2 0.0 9.4p. oil 3 1.0 0.7 0.6 3.0 10.5 0.0 3.4 11.8 11.4 11.7 0.0 1.2 0.0 5.6 10.2 0.0 0.2 10.0 0.6p.seed 4 3.1 27.3 10.1 3.2 0.3 10.3 5.9 467.6 84.8 2.9 10.1 9.3 9.1 493.3 0.0 0.0 15.8 1.3 3.3p.seed 5 11.3 31.8 1.7 14.6 0.3 0.8 15.9 500.6 95.8 2.1 0.2 1.9 0.0 514.6 0.0 0.0 3.8 1.3 15.2p.seed 6 3.0 28.0 1.7 3.1 11.2 0.8 5.1 497.6 100.1 13.3 0.4 1.9 0.0 482.5 9.8 5.6 3.8 9.1 2.9

Fig. 1 Determination of Al, Co, Cr, Cu, Fe, Mn, Na, Zn in pumpkinoil, seeds and residue after oil extraction and digestion in themicrowave unit.

Fig. 2 Determination of Ca, K, Mg, P in pumpkin oil, seeds andresidue after oil extraction and digestion in the microwave unit.

J. Anal. At. Spectrom., 2003, 18, 54–58 57

Dow

nloa

ded

on 0

2 O

ctob

er 2

012

Publ

ishe

d on

11

Dec

embe

r 20

02 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/B20

9308

C

View Online

consuming and more samples can be digested at the same timecompared to open vessel and steel bomb digestion. Aftermicrowave digestion a good reproducibility for ICP-AES mea-surements of all elements was found. There is no limitation forthe determination of non-volatile metals that cannot be lostnormally by open vessel digestion. An addition of salt duringoil production causes approx. 10 times higher amounts of Ca,K, Mg, and Na than found for self extracted oil. Also in seedsand residues higher amounts of Na could be registered. No lossof volatile elements in pumpkin oil could be observed usingmicrowave digestion prior to the ICP-AES analysis of theelements. In general, recoveries for all elements in pumpkin oilsand seeds were w95%, only S could not be detected. The LODsof the elements in pumpkin oils were v0.1 mg g21 for Ca, Cd,Mg, Mn, Ti, and Zn, in the range from 0.1 to 0.8 mg g21 for Co,Cu, Fe, K, Mo, Na, Ni, Pb, and V, and higher than 0.8 mg g21

for Al, Cr, and P in pumpkin oil samples.

Acknowledgements

This work was supported by OEAD (Austrian AcademicExchange Service) scholarships (OEAD research scholarshipand Ernst Mach scholarship) in the course of a co-operationbetween Croatia and Austria (Croatian Ministry of Science andTechnology and Austrian Culture Institute).

References

1 L. Allen, P. H. Siitonen and H. C. Thompson, J. Am. Oil Chem.Soc., 1998, 75, 477–481.

2 A. Banks, E. Eddie and J. G. Smith, Nature, 1961, 190, 908–912.

3 A. J. DeJonge, W. E. Coenen and C. Okkerse, Nature, 1965, 206,573–577.

4 A. Mandl, G. Reich and W. Lindner, Eur. Food Res. Technol.,1999, 209, 400–406.

5 P. L. Buldini, D. Ferri and J. L. Sharma, J. Chromatogr., 1997,798, 549–555.

6 G. P. Blanch, M. D. Caja, M. L. R. del Castillo and M. Herraiz,J. Agr. Food Chem., 1998, 46, 3153–3157.

7 I. Karadjova, G. Zachariadis, G. Boskou and J. Stratis, J. Anal.At. Spectrom., 1998, 13, 201–204.

8 M. Maurillo, Z. Benzo, E. Marcano, C. Gomez, A. Garaboto andC. Marin, J. Anal. At. Spectrom., 1999, 14, 815–820.

9 R. Calapaj, S. Chiricosta, G. Saija and E. Bruno, At. Spectrosc.,1988, 9, 107–109.

10 F. J. Slikkerveer, A. A. Braad and P. W. Hendrikse, At. Spectrosc.,1980, 1, 30–35.

11 K. Pomazal, C. Prohaska, I. Steffan, G. Reich and J. F. K. Huber,Analyst, 1999, 124, 657–663.

12 C. Prohaska, K. Pomazal, I. Steffan and A. Torvenyi, J. Anal. At.Spectrom., 2000, 15, 97–99.

13 C. Feldman, Anal. Chem., 1974, 46, 1609–1613.14 E. Tserovsky and S. J. Arpadjan, J. Anal. At. Spectrom., 1991, 6,

487–491.15 P. W. J. M. Boumans, Basic Concepts and Characteristics of

ICP-AES, Inductively Coupled Plasma Emission Spectroscopy.Part I, Methodology, Instrumentation, and Performance, ed.P. W. J. M. Boumans, Wiley, New York, 1987, ch. 4.

16 J. L. Fabc and M. L. Ruschak, Anal. Chem., 1985, 57, 1853–1856.17 I. M. Goncalves, M. Murillo and A. M. Gonzale, Talanta, 1998,

47, 1033–1042.18 M. Guardia and M. T. Vidal, Talanta, 1984, 31, 799–803.19 W. J. Price, J. T. H. Roos and A. F. Clay, Analyst, 1970, 95, 760–

762.20 R. C. Richter, D. Link and H. M. Kingston, Anal. Chem., 2001, 1,

30–37.

58 J. Anal. At. Spectrom., 2003, 18, 54–58

Dow

nloa

ded

on 0

2 O

ctob

er 2

012

Publ

ishe

d on

11

Dec

embe

r 20

02 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/B20

9308

C

View Online