2.2 Sample Preparation
Samples were analysed directly. 2 mg/L Sc was added as internal standard. 2.3 Calibration Standards
The calibration standards were prepared from 1000 mg/L single element standards by dilution. To match the matrix, 15% Ethanol was added to all solutions. In order to correct for the varying matrix, ‘Smart Background Correction’ was applied, using four separate samples with varying Ethanol concentrations. 2 mg/L Sc was used as internal standard. The concentrations are given in Tables 3 and 4.
Table 3. Calibration Standards. Blank 0
Al [mg/l] As [mg/l] B [mg/l] Br [mg/l] Cd [mg/l] Cu [mg/l] Fe [mg/l] Mn [mg/l] Pb [mg/l] Sn [mg/l] Zn [mg/l]
Sc [mg/l]
S-1 0.1
0 0.05 0 0
0 0.05 0 0.05 0 0.05 0 0.05 0 0.05 0 0.05 0 0.05
2 Ethanol [% ] 15 2 15
0.1 0.1
S-2 1
0.5 1 1
0.5 0.5 0.5 0.5 0.5 0.5 0.5
2 15
S-3 S-4 2.5
3. Results and Discussion
Table 5 shows the selected wavelengths and the limits of detection (LOD). The LODs were calculated according to the equation [6]:
LOD = 3 RSDb
Where: RSDb
c - - SBR - 5
1.25 2.5 2.5 2.5
1.25 2.5 1.25 2.5 1.25 2.5 1.25 2.5 1.25 2.5 1.25 2.5 1.25 2.5
2 2 15 15
Table 4. Smart Background Correction Standards. SBC-1 SBC-2 2
Sc [mg/l] Ethanol [% ] 20 2 15 10
5 5
c/SBR
relative standard deviation of 10 replicates of the blank
concentration of the standard signal to background ratio
Table 5 shows the 3 sigma detection limits for a selection of lines in a 15% Ethanol-Water matrix. The values show that the requirements of the regulations can be met. Figure 1 shows the strongly structured spectrum in the VUV/UV spectral region between 147 and 189 nm. While most elements have their most prominent spectral lines above 200 nm, where such effects are minimal, the sensitive spectral lines of As and Sn at 189 nm and also the most sensitive line of Al at 167 are affected by the emission spectrum of carbon species. In addition to the structure, depending on the carbon species concentration in the sample, the background level shows strong variations, which makes analysis difficult. By utilising a novel pixel intensity based correction approach and solutions containing the relevant matrix components, Smart Background Correction, enables the modelling and
SBC-3 SBC-4 2
2 5
Table 5. Limits of detection (LOD) for the selected lines in a 15% Ethanol-Water matrix. Element
Line (nm)
Al Al Al
As As B B
Br
Cd Cd Cd Cu Cu Cu Fe Fe Fe
Mn Mn Mn Pb Pb Pb Sn Sn Sn Zn Zn Zn
167.078 308.215 396.152 189.042 193.759 249.677 249.773 154.065 214.438 226.502 228.802 224.700 324.754 327.396 238.204 239.562 259.941 257.611 259.373 260.569 168.215 220.353 405.778 140.045 147.516 189.991 202.613 206.191 213.856
LOD (3 ) [ g/L]
0.9 4.8 3.5
12.6 17.6 2.6 1.3
113 0.4 0.5 0.8 2.1 1 1
0.9 2.3 1.5 0.2 0.2 0.3
25.4 7.2
34.3 22.5 16.3 10.1 0.5 0.9 0.3
Table 6. Spike recovery results of a selection of wines. Al 167.078
Cabernet
Cabernet-Spike Spike
Recovery [%] Red Table Wine
Red Table Wine-Spike Spike
Recovery [%] Cabernet Rose
Cabernet Rose-Spike Spike
Recovery [%] Chardonnay
Chardonnay-Spike Spike
Recovery [%] Cabernet
Cabernet-Spike Spike
Recovery [%] Red Table Wine
Red Table Wine-Spike Spike
Recovery [%] Cabernet Rose
Cabernet Rose-Spike Spike
Recovery [%] Chardonnay
Chardonnay-Spike Spike
Recovery [%]
mg/l 1.021 1.188 0.200 97.3
0.510 0.672 0.200 94.6
0.826 1.033 0.200 100.7 0.794 1.002 0.200 100.8
Fe 238.204 mg/l
3.175 3.223 0.100 98.4
2.632 2.736 0.100 100.1 1.729 1.851 0.100 101.2 1.533 1.677 0.100 102.7
As 189.042 mg/l
0.040 0.145 0.100 103.6 0.023 0.122 0.100 99.2
0.043 0.152 0.100 106.3 0.031 0.135 0.100 103.1
1.177 1.219 0.100 95.5
0.431 0.523 0.100 98.5
1.522 1.635 0.100 100.8 1.127 1.254 0.100 102.2
subsequent subtraction of the background spectrum, which effectively eliminates the influencing effects from the carbon matrix (Figure 2). This ultimately enables calibration and sample measurement of the effected elements even in cases, where the background is drastically different. Prior knowledge of the matrix concentration is not required, since SBC utilises the spectral region surrounding the spectral line to model and match the spectrum. In order to verify precision and accuracy, a selection of different wines, with alcohol concentrations, ranging from 9% -15% were examined and spike recovery measurements were performed. Excellent recoveries are found for all elements and samples (Table 6). For concentration in the ppm range a relative precision between 0.5% and 1% was obtained for replicate measurements.
4. Conclusion
The ability to determine trace elements in Wine utilising direct aspiration without prior sample digestion was demonstrated using the Spectro ARCOS with radial plasma observation. Other alcoholic beverages can be analysed using the same methodology.
Without the usually required digestion procedure, preparation related errors are eliminated and the total analysis time is drastically reduced. Additional advantages of the ICP-OES method are the high linear calibration range and the short analysis time. ICP-OES is thus a cost efficient way for the quality control of wines.
B 249.773 mg/l
7.690 7.768 0.200 98.5
6.279 6.508 0.200 100.4 6.497 6.823 0.200 101.9 6.740 7.120 0.200 102.6
Mn 257.611 Pb 220.353 mg/l
mg/l 0.006 0.097 0.100 91.5
0.009 0.102 0.100 93.6
0.006 0.099 0.100 93.4
0.010 0.106 0.100 96.4
Br 154.065 mg/l
1.483 1.642 0.200 97.6
0.372 0.640 0.200 111.9 0.974 1.224 0.200 104.3 0.847 1.113 0.200 106.3
Sn 189.991 mg/l
0.045 0.140 0.100 96.6
0.028 0.121 0.100 94.5
0.033 0.132 0.100 99.2
0.037 0.135 0.100 98.5
Cd 226.502 Cu 324.754 mg/l
0.003 0.098 0.100 95.1
0.000 0.092 0.100 92.0
0.000 0.098 0.100 98.0
0.000 0.099 0.100 99.0
Zn 213.856 mg/l
2.143 2.211 0.100 98.6
0.243 0.346 0.100 100.9 0.577 0.691 0.100 102.1 0.977 1.102 0.100 102.3
mg/l 0.039 0.138 0.100 99.3
0.134 0.232 0.100 99.1
0.042 0.145 0.100 102.1 0.143 0.249 0.100 102.5
Figure 1. Emission Spectrum of Carbon Species- @ Sn 147, Al167, Pb168 and As189 nm.
Figure 2. Correction of Molecular Interferences.
Spectroscopy Focus
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32
