Simultaneous determination of nitrate and nitrite in spinach and meat by ion chromatography

Significance of the topic

The occurrence of nitrite and nitrate in food products, both as added preservatives in processed meats and as natural components in vegetables, has significant health implications. Nitrite can react with amines to form carcinogenic N-nitroso compounds, while nitrate reduction in the human body may generate additional nitrite. Regulatory limits and accurate monitoring of these ions in complex matrices are essential for food safety and public health.

Goals and overview of the study

This work aimed to develop and validate an ion chromatography (IC) method for simultaneous determination of low concentrations of nitrite and nitrate in meat homogenates and slurried spinach. The focus was on achieving high sensitivity, precision, and robustness using a high-capacity IonPac AS11-HC column with suppressed conductivity detection.

Methodology and Instrumentation

• Sample extraction with deionized water, followed by centrifugation and 0.22 µm filtration.
• Cleanup using OnGuard II RP cartridges for hydrophobic removal and layered OnGuard II Ag/H cartridges to eliminate halides and residual silver.
• Chromatographic separation on a Dionex IonPac AS11-HC column (2 × 250 mm) with KOH gradient elution (5–50 mM) generated by an EGC 500 KOH cartridge.
• Detection via suppressed conductivity using an ADRS 600 suppressor in recycle mode at 48 mA and 15 °C.
• Calibration over 5–1500 µg/L for nitrate and 5–500 µg/L for nitrite, with linearity coefficients (r2) > 0.999.

Main results and discussion

• Baseline resolution of nitrite and nitrate from matrix anions within a 20 min run time.
• Limits of detection (LOD): 1.33 µg/L for nitrite, 2.26 µg/L for nitrate; LOQs: 4.42 and 7.52 µg/L respectively.
• Precision (n=9): retention time RSD < 0.2%, peak area RSD < 5%.
• Recovery in spiked meat homogenate and spinach: 89–100% for nitrite and nitrate.
• Measured contents: meat homogenate contained 0.597 mg/kg nitrite and 24.2 mg/kg nitrate; spinach showed nitrate at 130 mg/kg and nitrite below LOQ.

Benefits and practical applications

The method’s high sensitivity and selectivity support regulatory compliance testing of nitrite and nitrate in food products. Large injection volumes on the high-capacity column reduce the need for extensive pre-concentration, streamlining routine analysis in quality control and research laboratories.

Future trends and opportunities

Emerging coupling of IC with mass spectrometry will improve specificity and reduce interferences. Automation of sample cleanup and miniaturized IC systems will enhance throughput. Data analytics and predictive modeling may further optimize method performance and assist in risk assessment in food safety monitoring.

Conclusion

A robust IC method using a high-capacity IonPac AS11-HC column and suppressed conductivity detection was established for simultaneous analysis of nitrite and nitrate in meat and leafy vegetables. The approach offers low detection limits, excellent linearity, and reliable recoveries, making it suitable for routine food safety applications.

Reference

1. Gangolli SD, van den Brandt PA, Feron VJ, et al. Nitrate, nitrite and N‐nitroso compounds. Environ Toxicol Pharmacol. 1994;2(1):1–38.
2. Lundberg JO, Carlström M, Weitzberg E. Metabolic effects of dietary nitrate in health and disease. Cell Metab. 2018;28:9–22.
3. European Commission. Decision No 1129/2011/EC of 11 November 2011. Off J Eur Union L295:1–177.
4. Maynard D, Barker A, Minotti P, Peck N. Nitrate accumulation in vegetables. Adv Agron. 1976;28:1–32.
5. EFSA. Scientific opinion on nitrate in vegetables. EFSA Journal. 2008;689:1–79.
6. Siu DC, Henshall A. Ion chromatographic determination of nitrate and nitrite in meat products. J Chromatogr A. 1998;804(1-2):157–160.
7. Saccani G, Tanzi E, Cavalli S, Rohrer J. Determination of nitrite, nitrate, and glucose-6-phosphate in muscle tissues by IC/MS. J AOAC Int. 2006;89(3):712–719.
8. Kissner R, Koppenol WH. Qualitative and quantitative determination of nitrite and nitrate with ion chromatography. Methods Enzymol. 2005;396:61–68.
9. Thermo Fisher Scientific. AN112: Determination of Nitrate and Nitrite in Meat Using HPAEC. 2019.
10. Thermo Fisher Scientific. IonPac AS11-HC Columns Manual. 2019.
11. Thermo Fisher Scientific. OnGuard II Cartridges Manual. 2019.