2 Determination of Boron in Turkish Wines by Microwave Plasma Atomic Emission Spectrometry
2 Determination of Boron in Turkish Wines by Microwave Plasma Atomic Emission Spectrometry
2 Determination of Boron in Turkish Wines by Microwave Plasma Atomic Emission Spectrometry
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 June 2014
Received in revised form
25 November 2014
Accepted 26 November 2014
Available online 5 December 2014
Boron in various Turkish red wine and white wine samples was determined by microwave plasmaatomic emission spectrometry (MP-AES) at 249.677 nm. MP-AES is a novel instrument which provides
a low-cost analysis based on a micro-wave plasma generated with nitrogen. Wine samples were not pretreated prior to analysis. The recovery rate of boron added to the 1:1 diluted wine samples was around
80% which showed interference due to the matrix of the wine samples. Therefore standard addition
method was used for quantications. The limit of detection and limit of quantication were 0.08 and
0.28 mg mL1, respectively. A satisfactory linearity (r2 > 0.999) was obtained up to 10 mg L1 of boron. The
range of boron concentrations in various wine samples was 4.2e10.8 mg L1.
2014 Elsevier Ltd. All rights reserved.
Keywords:
Boron
Microwave plasma eatomic emission
spectrometry
Wine
1. Introduction
Boron (B) is a non-metallic element which is a common constituent of foods since it accumulates to plants from boron-rich
soils and also some boron compounds used as preservatives for
foods. Boron deprivation effects bone development, brain functions, macromineral metabolism, energy substrate utilization, immune function and insulin secretion (Nielsen, 1997). According to
World Health Organization, a tolerable daily intake (TDI) in human
consumption is 0.16 mg B per kg body weight (WHO., 2003).
Boron can be determined using various analytical methods such
as ame atomic absorption spectrometry (FAAS) (Mihaljevic, Sebek,
Lukesova, & Bouzkova, 2001), electrothermal atomic absorption
spectrometry (ETAAS) (Burguera, Burguera, Rondon, & Carrero,
2001), inductively coupled plasma mass spectroscopy (ICP-MS)
(Hokura, Matsuura, Katsuki, & Haraguchi, 2000) and inductively
coupled plasma atomic emission spectroscopy (ICP-OES) (Krejcova
& Cernohorsky, 2003). Since boron is a thermally refractive element
and forms stable carbides, its sensitivities in ETAAS and FAAS are
low causing high limit of detection (LOD) values. Therefore, it can
be determined by nitrous-oxide acetylene ame or by ETAAS only
at high atomization temperature and prolonged times. Nevertheless, high LOD values restrict the determinations of low
533
Cr, Ni, Pb and V in gasoline and ethanol fuel (Donati, Amais, Schiavo,
& Nobrega, 2013) and nally Hettipathirana determined B in hightemperature alloy steel (Hettipathirana, 2013).
In this study, a novel method was described for the determination of boron in wine samples using MP-AES. The calibration
techniques were compared and the experimental/instrumental
parameters were optimized. Finally, boron concentrations in
different wine samples were determined.
2. Experimental
2.1. Instrumental
All experiments were carried out with Agilent 4100 MP-AES
which is equipped with Inert One Neb nebulizer and double-pass
glass cyclonic spray chamber (Agilent Technologies, Melbourne,
Australia). Nitrogen was obtained from air using a F-DGSi, Thyster
8/1 LV, (Innovative Gas System Co., Evry, France), nitrogen generator. Prior to reading samples, 10 s for uptake time, 20 s for torch
stabilization time is set. For all experiments, 5 s read time with 5
replicates was xed. Before starting to study torch alignment and
wavelength calibration were carried out automatically by the instrument using a wavelength calibration solution (Agilent
Technologies, Melbourne, Australia, 2013).
2.2. Reagents and solutions
Water with 18.2 mU cm resistivity obtained by a TKA reverse
osmosis and a TKA deionizer system (TKA Wasseraufbereitungsstandards, systeme GmbH, Niederelbert Germany) was used for all
dilutions. Calibration standards were prepared from 1000 mg L1 of
boron solution (Carlo Erba, Radona, Italy) daily. Red wine and white
wine samples produced in different regions of Turkey from
different grape varieties were bought from markets.
2.3. Procedure
The boron concentrations in Turkish wines were determined
applying by standard addition technique. For this purpose, 5 mL
aliquots of samples were completed to 10 mL with distilled water
and standards. The External Gas Control Module (EGCM) was used
to inject air into plasma to burn-off carbon. Results were given as
the average of at least 5 replicate analyses. Blanks were prepared in
10% (v/v) ethanol in water to maintain the same plasma temperature and aspirating rate for the sample and the blank solutions.
3. Results and discussion
3.1. Optimization for boron determination by MP-AES
To obtain the highest sensitivity, the instrumental working parameters such as nebulizer pressure and viewing position were
optimized by the instrument automatically and then ne adjustments were made. Nebulizer pressure was set to 120 kPa whereas
viewing position set to 20. The calibration curves were formed at
249.772 nm, 208.889 nm, 249.677 nm, 208.957 nm and
330.244 nm. The highest slopes (i.e. sensitivity) were obtained at
249.772 and 249.677 nm with perfect linearity (r2 > 0.999) in a
wide range up to 10 mg L1 which includes the boron concentrations of samples even with standard addition technique (Fig. 1).
Although the working range could be further extended providing
non-linear calibration using rational tting, the concentration of
the analyte in the samples were low enough to work in the linear
range.
Fig. 2. Effects of ethanol content on the emission signal for 1 mg L1 of boron. Error
bars present standard deviation of 5 replicates.
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Table 1
Recovery test for boron added to 10 fold diluted wine samples (N:5).
Added
e
1
2
e
1
2
0.54
1.45
2.61
0.87
1.89
2.85
mg L1
mg L1
mg L1
mg L1
Recovery (%)
e
94
102
e
101
99
0.02
0.13
0.12
0.13
0.12
0.15
Mean SD.
found by linear calibration against aqueous standards and standard addition techniques were not signicantly different. However, upon excessive dilution, there is a risk of falling below LOD.
In this study, to detect lower concentrations of boron, standard
addition was preferred to stay above LOD. The TDS values of
arbitrarily selected white wine and red wine samples determined
gravimetrically were below 1.5%. Since the TDS concentration of
wine was low enough not to cause any salt accumulation all determinations were performed without damaging of torch during
the whole analysis.
Table 2
Boron contents of some red and white wine samples with their region, grape type and the year of recolte (N:5).
White wine
Red wine
Region
Grape type
Recolte
year
Boron
content (mg L1)*
Region
Grape type
Recolte year
Eastern AnatoliaTokat/Erba
Narince
2011
5.44 0.12
Kalecik Black
2012
8.75 0.13
Central Anatolia
Ankara/Kalecik
Aegean Denizli
Thrace
Narince-Chardonay
2012
5.14 0.14
Kalecik Black
2012
7.94 0.15
Sultaniye
Sultaniye-Semillon
2011
2012
4.42 0.16
4.48 0.13
Merlot
Angora
2012
2012
8.10 0.13
4.88 0.12
Thrace
Sultaniye-Semillon
2008
4.12 0.15
Angora
2011
4.94 0.16
Thrace
Sultaniye-Semillon
2008
4.56 0.14
Angora
2012
9.33 0.17
Thrace
Thrace
Aegean
Aegean
Sultaniye-Semillon
Sultaniye-Semillon
Muskat
Muskat
2012
2008
2009
2010
4.66
5.02
5.10
5.36
Central Anatolia
Ankara/Kalecik
Central Anatolia
Ankara/Kalecik
Aegean Denizli
Central Anatolia
Ankara
Central Anatolia
Ankara
Central Anatolia
Ankara
Aegean Denizli
Aegean
Aegean
Aegean
alkaras-Merlot
Cabarnet Sauvignon-Shiraz-Merlot
Cabarnet Sauvignon-Shiraz-Merlot
Cabarnet Sauvignon-Shiraz- Merlot
2012
2012
2010
2011
Mean SD.
0.18
0.13
0.12
0.12
Boron content
(mg L1)*
6.32
10.72
10.44
10.75
0.14
0.13
0.12
0.12
4. Conclusion
The trace concentration of boron in wine samples were successfully determined using a cost-efcient nitrogen micro-wave
plasma optical emission spectrometry. No spectral interference
was observed due to overlapping the emission lines for boron and
matrix components. The running costs are much lower than AAS
and especially ICP. In addition, ammable gases are not used which
makes the MP-AES safer compared to FAAS. On the other hand, the
LOD values were better (lower) than FAAS but not as low as ICP-MS.
The method is fast and suitable for sequential multi-element
analysis. Standard addition calibration was preferred and advised
to compensate errors due to the non-spectral interferences originated from the differences between the sensitivities for boron in
the sample and calibration standard.
Acknowledgments
We are grateful to Agilent Technologies and SEM, Agilent
Authorized Distributor in Turkey, for providing MP-AES 4100
spectrometer.
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