Determination of formaldehyde in aquatic products (3)

2 High performance liquid chromatography

1 Principle

Formaldehyde was derivatized with 2,4-dinitrophenylhydrazine under acidic conditions in a water bath at 60°C to generate 2,4-dinitrophenylhydrazon.

2 Instruments

1 High performance liquid chromatography with UV detecto.

2 High-speed centrifug.

2, 3 10 mmX150 mm stoppered glass colum.

4 Constant temperature water bat.

5 Vortex mixe.

6 Pipette: 1mL; Micro injector: 20 μL; 5mL colorimetric tube with stoppe.

7 22 μm filte.

3 Reagents

1 Methanol: chromatographically pure, used after filtration and degassin.

2 Dichloromethan.

3 2,4--Nitrophenirone solution: Weigh 100 mg of 2,4--nitrophenylphenidate and dissolve it in 24 mL of concentrated hydrochloric acid, add water to make up to 100 m.

4 Formaldehyde standard stock solution: see 8 of this standard for preparation and calibration, and dilute to 20 μg/mL for temporary us.

5 Anhydrous sodium sulfate: calcined at a high temperature of 550°C, stored in a desiccator and cooled before us.

4 Determination steps

1 Sample processing

Take 1 mL~0 mL of the steam distillate prepared in 4, place it in a 5 mL colorimetric tube with a stopper, add distilled water to 0 mL, and add 2 mL of 2,4-dinitro The benzophenone solution was placed in a 60°C water bath for 15 min, then rapidly cooled in running water, 2 mL of dichloromethane was added, vortex mixer was shaken and extracted for 1 min, 3 000 r/min, centrifuged for 2 min, and the supernatant was taken out agai.

2 Chromatographic conditions

1 Chromatographic column: ODS-C18 column, 5 μm, 6 nm × 250 n.

2 Column temperature: 40°.

3 Mobile phase: methanol + water (60+40), 5 mL/mi.

4 Detector wavelength: 338 n.

3 Drawing of standard curve

Take 0 mL, 1 mL, 25 mL, 5 mL, 75 mL, L 0 mL of 20 μg/mL formaldehyde application solution (equivalent to 0 μg, 2 μg, 5 μg, 10 μg, 15 μg, 20 μg) in 5 mL with a plug rati.
In the color tube, add distilled water to 0 mL, and take 20 μL for injection after processing according to 1. According to the time of occurrence qualitatively (1 min), the peak area is quantitative, each concentration is done twice, the average value is taken, the peak area and formaldehyde content are plotted, and the standard curve is draw.
Take 20 μL of sample treatment solution and inject it into liquid chromatography to measure the integral area and find out the corresponding concentration from the standard curv.

5 Result calculation

The content of formaldehyde in the sample was calculated according to formula (3), and the calculation result was kept to 2 decimal place.

where:

X ₃ — formaldehyde content in aquatic products, in milligrams per kilogram (mg/kg);

C3 _— curve results, in micrograms per milliliter (μg/mL);

M ₃ — sample mass, in grams (g);

V ₃ - the volume of the distillate taken from the sample measurement, in milliliters (mL);

200——The total volume of the distillate, in milliliters (mL.

6 Recovery rate

The recovery rate calculated by adding formaldehyde standard solution to the sample distillate is > 90 .

7 Precision

2 independent assays were obtained under repeatable conditions:

When the formaldehyde content in the sample is less than or equal to 5 mg/kg, the relative deviation is less than or equal to 10%; when the formaldehyde content in the sample is greater than 5 mg/kg, the relative deviation is less than or equal to 5.

8 Detection limit

The detection limit of formaldehyde in the samples was 20 mg/k.