1. Describe 

Nitrite, primarily referring to sodium nitrite, is a white to light yellow powder or granular substance with a slightly salty taste and high water solubility, resembling table salt in appearance and taste. It is widely used in industries such as construction and is permitted in limited quantities as a color fixative in meat products. However, sodium nitrite poisoning is a significant risk, with ingestion of 0.3–0.5g potentially causing toxicity or death. Therefore, measuring nitrite content is a critical aspect of food safety testing. 

During the processing of edible bird's nests, alum may potentially be used as an additive to enhance the whiteness or shape of the nests, while nitrites may originate from storage conditions or emerge during processing.

According to China's current food safety standards:

1. Alum is prohibited as an additive in bird's nest products.

2. Nitrite content is strictly limited to 30 mg/kg.

Therefore, all bird's nest products imported into China must comply with these regulations.

2. Limit of detection

Standard solution: 0.1mg/L; 

Sample: 1mg/kg. 

Range of detect: 0-5mg/L for liquid samples and 0-100mg/kg for solid samples. 

3. Kit composition 

Detection Solution A (6mL) ×1

Detection Solution B ×1

Droppers ×100

1.5mL Centrifuge tubes x100

50mL Centrifuge tubes x5

Colorimetric card ×1

User manual

The reagents and appliances may be required but not provided: scissor or cutting knife, pipette, purified or distilled water, ultrasonic apparatus, centrifuge, and colorimetric tube or beaker. 

4. Specifications 

100 tests 

5. Reagent preparation 

Before test, add 6mL of pure water or distilled water into the bottle of Detection Solution B, tighten the cap, and shake well to dissolve. Note: Store in a refrigerator at 4°C after use.

6. Procedure & steps 

6.1 Liquid samples: Colorless or light-colored liquid samples can be directly taken as the sample test solution. 

6.2 Solid samples: Take 1g of the finely chopped sample and put it into a medicine cups, 50mL centrifuge tube, colorimetric tube, or beaker. Add 10mL of purified or distilled water, then process ultrasound for 10min, stirring occasionally. Let it stand for 5min until the upper layer is clear (or centrifuge at 3000rpm for 2min). Use the supernatant as the test solution. 

6.3 Take 1mL of the test solution into a 1.5mL centrifuge tube, then add 1 drop of Detection Solution A and 1 drop of Detection Solution B in sequence. Cap the tube, shake well, and let it react for 5min. Observe the color change.

7. Results determination

If the solution shows an obvious purple-red color, it indicates the presence of nitrite in the sample. The deeper the color, the higher the nitrite concentration. Semi-quantitative determination can be made by comparing with the standard colorimetric chart. 

8. Attention

8.1 Since nitrite is commonly present in drinking water, it cannot be used as the dilution solution for measurement. 

8.2 This method is a rapid on-site detection method, and accurate quantification should be based on the standard method. 

8.3 The centrifuge tubes provided in the kit can be reused after being cleaned thoroughly.

9. Limit standard

The specific nitrite limit standards for food should be referenced according to local regulations. The table on the reverse side shows

the standards in China, provided for reference only. 

10. Storage conditions 

Store at room temperature with seal, away from light, and in a well-ventilated and dry place. The shelf-life is 12 months.