Determination of nitrate in vegetables by continuous flow: interlaboratory study

Area of Science:

• Food Chemistry
• Analytical Chemistry
• Environmental Science

Background:

• Nitrate levels in leafy vegetables are a significant concern for food safety and human health.
• Accurate and reliable analytical methods are crucial for monitoring nitrate content in produce.

Purpose of the Study:

• To collaboratively study and validate a continuous flow (CF) method for determining nitrate concentrations in various leafy vegetables.
• To assess the method's accuracy, repeatability, and reproducibility across multiple laboratories.

Main Methods:

• Leafy vegetable samples (endive, lettuce, spinach, beetroot) were extracted with water and filtered.
• Nitrate was reduced to nitrite using metallic cadmium within a CF system.
• Nitrite was quantified colorimetrically after reaction with sulfanilamide and N-1-naphthylethylenediamine at 530 nm.

Main Results:

• The proposed CF method was analyzed by 13 laboratories on 14 vegetable samples (including blind duplicates) with nitrate levels ranging from 900 to 5200 mg/kg.
• Repeatability relative standard deviation (RSDr) values ranged from 1.7% to 5.5%.
• Reproducibility relative standard deviation (RSDR) values ranged from 3.3% to 5.9%, indicating good method performance.

Conclusions:

• The continuous flow method is a reliable and precise technique for the determination of nitrate in leafy vegetables.
• The method's performance characteristics support its application in routine food analysis and regulatory monitoring.