Waters total solution for dicyandiamide determination in dairy products

Waters total solution for dicyandiamide determination in dairy products

Ding Juanjuan, Ji Yinghua, Wang Bing, Cai Wei Water Technology (Shanghai) Co., Ltd.

Summary
In January 2013, New Zealand milk and dairy products were found to contain small amounts of the toxic substance dicyandiamide, and the New Zealand government has ordered the ban on the sale of milk products containing dicyandiamide. Since China is a major exporter of dairy products in New Zealand, this sensitive food safety issue has once again touched the hearts of the entire Chinese people. Waters ^® has launched a complete solution for the first time, providing a powerful analytical tool for our customers. Dicyanamide (commonly known as dicyandiamide), abbreviated DICY or DCD, is a dimer of cyanamide and a cyano derivative of hydrazine. Chemical formula C ₂ H ₄ N ₄ , white crystalline powder, soluble in water, alcohol, ethylene glycol and dimethylformamide, almost insoluble in ether and benzene. Non-flammable, stable when dry.

Difficulties in analysis <br>The polarity of dicyandiamide is very large. Traditional C ₁₈ columns and HILIC columns are difficult to retain. For complex dairy substrates, they will co-elute with impurities, affecting the quantification and characterization of target compounds. Waters' BEH Amide series of columns provide excellent retention of dicyandiamide through a three-bonded amide-bonded phase and hydrophilic interaction chromatography.

experimental method
First, the sample preparation method:
1 g of milk powder and 10 mL of 1% trichloroacetic acid were dissolved and the protein was precipitated, and centrifuged at 12,000 rpm for 10 min. 2 mL of the supernatant was applied to a SepPak ^® AC2 cartridge (Sep-pak AC2 was connected to a 30 mL reservoir, wat011390). Follow the procedure below. The method recovery rate was 91%.

Second, the instrument method :
UPLC ^® method:
Instrument: ACQUITY UPLC ^®
Mobile phase A: 0.05% acetic acid water mobile phase B: 0.05% acetic acid acetonitrile column: BEH Amide 2.1 × 150 mm 1.7 μm
Flow rate: 0.3 mL/min
Column temperature: 30 ° C
Injection volume: 5 μL
Gradient curve:

MS parameters:
Capillary voltage: 3.5 kv
Desolvation gas temperature: 400 °C
Desolvent gas flow rate: 900 L/hr
Collision gas flow rate: 0.2 mL/min

Experimental results:

Reproducibility:

Detection weapon 1 - RADAR ^TM function

During the detection process, it was found that even if the dairy substrate was purified, the background interference was still serious. Therefore, the RADAR function was turned on during the detection process to monitor the interference of the impurity on the target compound and the influence of the background matrix in real time.

This figure is a multi-reaction detection channel and a full scan of the substrate for simultaneous detection of the target compound. The target compound dicyandiamide peak time background interference is not obvious, and the ion suppression effect is minimized.

Detection tool 2 - PICs function (child ion confirmation scan)
When detecting the target compound, it is found that the molecular weight of the substance itself is small, there are many interfering substances in the dairy product, and the interference is serious, and a false positive will inevitably occur. At this time, high-resolution mass spectrometry is selected for molecular weight and structure analysis, Waters Xevo ^® series quadrupole mass fragment ions can provide information to enable multiple injection to complete a qualitative compound.

It can be seen from the figure that the main fragment ions in the PICs mass spectrum of the solvent standard and the milk powder sample are the same, and the relative intensity ratio between the fragment ions is also within the error range, and the fitting degree is well matched, and it can be confirmed that it is a positive sample. This adds a qualitative function to a single-deterministic method that provides only two pairs of ion contrasts, making the data more accurate.

Conclusions <br>Licyandiamide is very polar, traditional C ₁₈ columns and HILIC columns are difficult to retain, while Waters Amide series columns are bonded via a three-bonded amide-based phase, hydrophilic interaction chromatography. The principle is that dicyandiamide is very well retained. The instrument provides a better interpretation of the residue in complex matrices. For example, the RADAR function for real-time detection of background matrix interference and the PICs function for multiple qualitative selections can be well applied in our actual work. Make our work more effective.