FAST Flame Atomic Absorption for the Analysis of Copper in Wine

With the popularity of wine consumption continuously growing in China, regulations on the safety and quality of wine are being applied.

Today, wine imports into China are compelled to meet mandated elemental limits and upon arrival are subjected to local testing. If a wine does not meet the specifications as detailed in Table 1, it can be either destroyed or returned to its point of origin.

These elements occur naturally in wine grapes and, as such, are typically present in the wine from which they are produced.

Concentrations of these elements may vary from variety to variety and region to region due to the presence of nutrients in the soil that the grapes are grown in, the absorption of these nutrients by the vine itself, and the production process by which the wine is made.

Because of this significant variation, there is no way to guarantee that a given wine meets the import regulations without undertaking analytical testing.

Therefore, because of the real possibility of the wine being rejected upon arrival into China and the potential financial impact that arises, wine producers and exporters are invested in finding a simple and accurate method for identifying the concentrations of elements of interest in their wine.

Table 1. Elemental limits on wines imported into China. Source: PerkinElmer Food Safety and Quality

Experimental

Nine different wines were purchased (Table 2) for the analysis of copper (Cu), iron (Fe), and manganese (Mn), utilizing the conditions detailed in Table 3. All analyses were conducted using a PerkinElmer PinAAcle™ 900T atomic absorption spectrometer functioning in flame mode.

A high-power nebulizer with the standard spray chamber and a 10 cm burner head was used. External calibrations were produced using a single intermediate standard made in 2% HNO₃ /deionized water which was subsequently diluted in-line using the full capacity of the PerkinElmer FAST Flame 2 sample automation accessory.

The highest standard surpassed the concentrations of the upper regulatory limit for each element to ensure a wide range of detectability. Wine samples were directly introduced without any preparation other than spiking using the FAST Flame 2 accessory. The FAST Flame 2 accessory combines a high-speed autosampler, peristaltic pumps, and switching valve.

It offers fast sample turnaround times with rapid rinse-out, short signal stabilization times and no sample-to-sample memory effect. The FAST Flame 2 sample automation accessory quickly fills a sample loop via vacuum and then shifts to inject the sample loop while the autosampler moves on to the next sample.

This eliminates the wait time affiliated with self-aspiration or peristaltic pumping and the long rinse-in and rinse-out times related to the autosampler movement and flushing, resulting in sample-to-sample times in as little as 15 seconds.

The FAST Flame 2 accessory has the capacity to mechanically pump the sample during injection which facilitates the optimization of nebulizer and flame conditions. This eliminates variability as a result of alterations in sample viscosity, dissolved solids, and tubing length, and also supplies long-term sample flow stability.

The capacity for in-line dilution enables the analyst to produce a single intermediate standard, and then the FAST Flame 2 accessory produces all calibration standards in-line automatically, as required.

Additionally, the instrument can be configured to determine QC over-range samples and then use the in-line dilution capability to re-run a sample that falls outside the calibration range at an increased dilution factor automatically to bring the signal within the calibration and supply precise measurements along with a validated QC check.

Each wine sample was spiked at levels both above and below the regulatory limit to evaluate the precision. The highest spike in each case was intentionally placed out of range of the calibration, and the instrument software identified and then auto-diluted the samples utilizing the in-line capacity of the FAST Flame 2 accessory.

This demonstrates the PinAAcle 900 AA spectrometer’s potential when paired with the FAST Flame 2 accessory to quickly evaluate samples precisely across a wide range of concentrations automatically.

Table 2. Wines analyzed. Source: PerkinElmer Food Safety and Quality

Table 3. PinAAcle 900T instrument and analytical conditions. Source: PerkinElmer Food Safety and Quality

Results and Discussion

The calibration curves were generated using the in-line dilution capabilities of the FAST Flame 2 accessory. Calibration results are displayed in Table 4.

The superb correlation for the calibration standards is indicative of the value of the automatic in-line sample and standard dilution supplied by the FAST Flame 2 accessory.

The independent calibration verification recoveries ensure that the calibration is valid and that the generation of standards via the dilution system is extremely accurate.

Tables 5-7 display the respective results for the analyses for copper, iron, and manganese. The results signify that the wines are well within the regulatory limits with the exception of the Australian chardonnay which is over the controlled limit for manganese.

From the limited samples analyzed, it can be seen that the 2 mg/L specification for manganese could be a key parameter when qualifying a wine for importation into China.

Spike recoveries for all elements are within 10% of spiked values, even when spikes were spiked below half of the regulated values and when diluted via the inline dilution feature of the FAST Flame 2 sample automation accessory, demonstrating the excellent accuracy required for successful analysis.

The inclusion of the FAST Flame 2 accessory limited the production of standards from one intermediate and three final standards to a single intermediate standard with a proportional reduction in human error throughout standard creation.

The FAST Flame 2 accessory had the capacity to react to the over-range spikes and auto-dilute the samples consistently and precisely without intervention from an analyst, saving time and getting rid of additional sample handling and re-prep.

These results show the strength and accuracy of the analysis, as well as demonstrating the speed and increased productivity the PinAAcle 900 AA spectrometer and the FAST Flame 2 accessory make possible.

Table 4. Calibration results. Source: PerkinElmer Food Safety and Quality

Table 5. Copper in wine (regulated limit = 1 mg/L). Source: PerkinElmer Food Safety and Quality

* = 5X Online Dilution

Table 6. Iron in wine (regulated limit = 8 mg/L). Source: PerkinElmer Food Safety and Quality

* = 5X Online Dilution

Table 7. Manganese in wine (regulated limit = 2 mg/L). Source: PerkinElmer Food Safety and Quality

* = 5X Online Dilution

Conclusion

This study showed the PinAAcle 900 AA spectrometer​​’s capacity to precisely measure Cu, Fe, and Mn across a range of wine samples at levels that meet the regulations set by China for imported wine.

User errors are minimized using the FAST Flame 2 sample automation accessory when carrying out dilutions and meeting calibration standards, boosting sample throughput.

For labs with low sample throughput, these same analyses can also be conducted without the FAST Flame 2 sample automation accessory.¹

References

1. Neubauer K., Lim S., "The Analysis of Copper, Iron, and Manganese in Wine with the PinAAcle 500", PerkinElmer Application Note.

Consumables

Table 8. Source: PerkinElmer Food Safety and Quality

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

For more information on this source, please visit PerkinElmer Food Safety and Quality.