Using FAST Flame Atomic Absorption for Copper, Iron, and Manganese Analysis in Wine

The increasing consumption of wine in China has led the country to implement rigorous regulations to ensure the quality and safety of the beverage. Wines that are imported to China undergo local testing upon arrival to ensure their compliance with regulatory limits for elemental concentrations. Wines that fail to comply with the regulatory limits given in Table 1 will either be destroyed or returned to their place of origin.

Table 1. Elemental limits on wines imported into China

Element Limit (mg/L)
Copper (Cu) 1
Iron (Fe) 8
Manganese (Mn) 2

The elements listed in Table 1 are naturally present in the grapes from which the wines are made.

Since the elements listed in Table 1 are naturally present in the grapes from which the wines are made, their concentrations can differ between regions and varieties due to the occurrence of nutrients in the soils used to grow grapes, the uptake of nutrients by the plants themselves, and the manufacturing process of wines.

The quality and safety of wine entering China is rigorously assessed. Image credit: Africa Studio / Shutterstock.com

The quality and safety of wine entering China is rigorously assessed. Image Credits: Africa Studio/shutterstock.com

This significant variability makes analytical testing the only way to ensure the compliance of wines with the import specifications of China. Therefore, wine manufacturers and exporters are interested in a convenient and accurate technique to determine elemental concentrations in their wine to avoid rejection of their products upon arrival to China.

Experimental Procedure

Table 2 lists nine different wines that were analyzed for copper (Cu), iron (Fe), and manganese (Mn) under the experimental conditions summarized in Table 3. A PerkinElmer PinAAcle™ 900T atomic absorption spectrometer running in flame mode was used to perform all analyses. A high-efficiency nebulizer coupled to a standard spray chamber and a 10 cm burner head was also used.

Table 2. Wines analyzed

Type Country of Origin Identifier
Cabernet Argentina AR Cab
Cabernet Australia AU Cab
Cabernet USA USA Cab A
Cabernet USA USA Cab B
Chardonnay Argentina AR Chard
Chardonnay Australia AU Chard
Chardonnay USA USA Chard A
Chardonnay USA USA Chard B
Red Zinfandel USA USA Zin

Table 3. PinAAcle 900T instrument and analytical conditions

Parameter Copper (Cu) Iron (Fe) Manganese (Mn)
Wavelength (nm) 324.75 248.33 279.48
Slit (nm) 0.7 0.2 0.2
Air Flow (L/min) 2.5 2.5 2.5
Acetylene Flow (L/min) 10 10 10
Integration Time (sec) 3 3 3
Replicates 3 3 3
Sample Flow Rate (mL/min) 6 6 6
Intermediate Standard 20 40 20
Auto-Diluted Calibration Standards (mg/L) 0.5, 2, 5 1, 4, 10 0.5, 2, 5
Calibration Curve Type Non-Linear Through Zero Non-Linear Through Zero Non-Linear Through Zero

A single intermediate standard in 2% HNO3 /deionized water was used to prepare external calibrations. This standard was subsequently diluted in-line with the PerkinElmer FAST Flame 2 sample automation accessory.

The FAST Flame 2 accessory equipped with a switching valve, peristaltic pump, and high-speed autosampler was used for injecting the samples. Apart from providing rapid sample turnaround with quick rinse-out, the FAST Flame 2 accessory eliminates memory effect between samples and ensures short signal stabilization times.

The sample loop is rapidly filled by the FAST Flame 2 accessory through vacuum and is then injected while the autosampler handles the next sample. This way, the time for self-aspiration or peristaltic pumping and the prolonged rinse-in and rinse-out times coupled to autosampler movement and flushing were eliminated, thus shortening sample-to-sample times to 15 seconds.

The mechanical pumping ability of the FAST Flame 2 accessory for sample injection allows for optimization of nebulizer and flame conditions, ensures steady sample flow for longer times, and eliminates deviations, all of which may be caused by changes in tubing length, sample viscosity and dissolved solids which can vary from sample to sample.

The in-line dilution capability of the FAST Flame 2 accessory enables automated generation of all required calibration standards in-line from a single intermediate standard.

It is also possible to set the FAST Flame 2 accessory to determine QC over-range samples. When this occurs, the sample is automatically diluted and rerun in order to ensure accurate measurements in conjunction with a passed QC check by bringing the signal in the calibration range.

Accuracy of the method was assessed by spiking of the samples at concentrations above and below the regulatory limits. In each case, the highest spike was purposefully beyond the calibration range and was identified and auto-diluted by the instrument software using the in-line dilution capability of the FAST Flame 2 accessory.

These capabilities show the advantage of using the combination of the PinAAcle 900 AA spectrometer and FAST Flame 2 accessory to evaluate samples rapidly and accurately at diverse concentration ranges with no operator intervention.

Experimental Results

The in-line dilution capability of the FAST Flame 2 accessory was used to create the calibration curves. The calibration results presented in Table 4 show very high correlation for the calibration standards, demonstrating the effectiveness of the automatic in-line sample and standard dilution capabilities of the FAST Flame 2 accessory. The Independent Calibration Verification (ICV) recoveries corroborate the validity of the calibration and accuracy of the standards created through the dilution system.

Table 4. Calibration results

Element Correlation Coefficient ICV Concentration (mg/L) ICV (% Recovery)
Copper (Cu) 0.99999 2 101
Iron (Fe) 0.99999 4 99.4
Manganese (Mn) 0.99983 2 102

The analytical results for Cu, Fe, and Mn are shown in Tables 5, 6, and 7, respectively. From the results, wines other than the Australian Chardonnay comply with the import specifications. The Mn concentration in the Australian Chardonnay is above the regulatory limits.

All elements were spiked at two levels: the regulated limit and half the regulated limit. All spike recoveries are within 10% of the spiked, demonstrating the high accuracy of the in-line dilution capability of the FAST Flame 2 and the accuracy of the methodology.

Table 5. Copper in wine (regulated limit = 1mg/L)

Wine Measured Conc. (mg/L) Measured Spikes Spike Recoveries %
0.5 mg/L 1.0 mg/L 10.0 mg/L * 0.5 mg/L 1.0 mg/L 10.0 mg/L *
AR Cab 0.046 0.558 1.08 10.4 103 104 104
AU Cab 0.603 1.11 1.61 10.8 100 101 102
USA Cab A 0.088 0.579 1.11 10.3 98.3 102 102
USA Cab B 0.088 0.611 1.12 10.8 105 103 107
AR Chard 0.013 0.527 1.03 10.5 103 101 105
AU Chard 0.478 0.969 1.38 10.3 98.2 90.3 98.6
USA Chard A 0.120 0.637 1.15 10.7 104 103 106
USA Chard B 0.099 0.609 1.13 10.8 102 103 1076
USA Zin 0.256 0.746 1.20 10.1 98.0 94.2 98.6

* = 5X Online Dilution

Table 6. Iron in wine (regulated limit = 8mg/L)

Wine Measured Conc. (mg/L) Measured Spikes Spike Recoveries %
1.0 mg/L 5.0 mg/L 20.0 mg/L * 1.0 mg/L 5.0 mg/L 20.0 mg/L *
AR Cab 1.80 2.72 6.78 21.4 92.1 99.5 97.9
AU Cab 2.18 3.20 7.35 22.8 103 104 103
USA Cab A 2.32 3.24 7.69 21.9 92.7 1085 98.1
USA Cab B 2.31 3.25 7.42 22.1 93.9 102 98.8
AR Chard 1.65 2.61 6.69 21.0 95.5 101 96.7
AU Chard 2.92 3.91 7.86 23.6 99.2 98.8 103
USA Chard A 1.68 2.67 6.62 21.3 98.7 98.8 98.1
USA Chard B 1.16 2.15 6.17 21.0 99.5 100 99.3
USA Zin 2.80 3.77 7.70 23.7 97.6 98.1 104

* = 5X Online Dilution

Table 7. Manganese in wine (regulated limit = 2mg/L).

Measured Spikes Spike Recoveries %

Wine Measured Conc. (mg/L) Measured Spikes Spike Recoveries %
1.0 mg/L 4.0 mg/L 10.0 mg/L * 1.0 mg/L 4.0 mg/L 10.0 mg/L *
AR Cab 1.36 2.31 5.20 11.0 95.0 95.9 96.0
AU Cab 1.93 2.90 6.07 12.3 97.1 104 104
USA Cab A 1.51 2.45 5.41 11.0 94.3 97.6 94.7
USA Cab B 1.50 2.45 5.45 10.9 94.5 98.8 93.9
AR Chard 1.01 1.98 5.03 10.5 97.2 101 94.4
AU Chard 2.09 3.07 6.29 12.4 97.2 105 103
USA Chard A 1.07 2.04 5.05 10.6 97.2 99.6 95.6
USA Chard B 0.968 1.94 4.96 10.8 97.1 99.8 97.8
USA Zin 1.67 2.66 5.85 11.9 98.6 105 102

* = 5X Online Dilution

Conclusion

The results clearly demonstrate the advantage of using the PinAAcle 900 AA spectrometer for accurate measurement of elemental concentrations of Cu, Fe, and Mn in different wine samples in order to confirm their compliance with Chinese regulatory limits for imported wines.

The use of the FAST Flame 2 accessory minimized human error in standard creation by reducing the formation of one intermediate and three final standards into a single intermediate standard, thus increasing sample throughput.

Over-range spikes were also identified, and consequently the samples were accurately auto-diluted with no operator intervention. This, in turn, reduced analysis time and eliminated additional sample handling and re-prep. Laboratories with low sample throughput can perform these analyses without a FAST Flame 2 accessory.

This information has been sourced, reviewed and adapted from materials provided by PerkinElmer.

For more information on this source, please visit PerkinElmer.

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