GB/T 21918-2008Determination of boric acid in foods (English PDF)

5.7 Vortex oscillator.

6.1 Preparation of standard curve

Accurately measure 0.00, 1.00, 2.00, 3.00, 4.00 and 5.00 mL of standard solutions; place

into 25 mL plastic tubes; add water to 5 mL respectively. Add 1 mL of sulfuric acid (1+1)

solution; oscillate to mix; then add 5.00 mL of EHD-CHCl3 solution; put the cover; put into

vortex oscillator to operate for about 2 min; stand still for layering; draw under layer's

EHD-CHCl3 solution; filter through Ø7cm dried fast filter paper.

Respectively take 1.00 mL of filtrate; place into 50 mL plastic tube; successively add 1.0

mL of turmeric-glacial acetic acid solution and 5 mL of concentrated sulfuric acid; oscillate

uniformly; stand still for 30 min; add 25 mL of anhydrous alcohol; after standing still for 10

min, measure absorbance at 550nm with 1 cm cuvette. Take standard series boric acid

amount (µg) as abscissa, and absorbance as ordinate; draw the standard curve.

6.2 Determination

6.2.1 Sample treatment

Solid samples. Weigh 2.00 g~10.00 g (accurate to 0.01 g) of samples; use high-speed

masher to mash; add 40 mL~60 mL of water and mix well; slowly add 2 mL of

concentrated sulfuric acid drop-by-drop; apply ultrasound for 10 min to promote the

dissolution and mixing. Add 5 mL of zinc acetate solution and 5 mL of potassium

ferrocyanide solution; add water to a fixed volume 100 mL; use as sample solution after

filtration. Take 1.00 mL~3.00 mL of sample solution according to the content of sample;

place into a 25 mL plastic tube; add water to 5 mL. Add 1 mL of sulfuric acid (1 + 1)

solution; oscillate to mix well. Then add 5.00 mL of EHD-CHCl3 solution; put the cover;

oscillator operates for 2 min; stand still for layering; draw under layer's EHD-CHCl3

solution; filter through Ø7cm dried fast filter paper.

Liquid samples. Weigh 2.00 g~10.00 g of samples (accurate to 0.01 g); add water to a

constant volume 100 mL as sample solution. For liquid samples with high protein or fat

content, 5 mL of zinc acetate solution may be added to the samples; add water to a

constant volume 100 mL and use it as sample solution. Take 1.00 mL~3.00 mL of sample

solution according to sample content; place into a 25 mL plastic tube; add water to 5 mL;

add 1 mL of sulfuric acid (1+1) solution; oscillate to mix well. Then add 5.00 mL of

EHD-CHCl3 solution; put the cover; vertex oscillator operates for about 2 min; stand still

for layering; draw under layer's EHD-CHCl3 solution; filter through Ø7 cm dried fast filter

volumetric flask; use 5% nitric acid solution to dilute and fix to constant volume;

concentration of this standard stock solution is equal to 10µg of boron per milliliter.

Prepared solution shall be timely transferred to a plastic bottle and be stored in

refrigerator at 0°C~4°C for 3 months.

9.10 Scandium standard working solution. 1.00 mg/L.

Draw 1.00 mL of scandium standard working solution and place into a 100 mL plastic

volumetric flask; use 5% nitric acid solution and fix to constant volume; each milliliter in

volumetric flask is equivalent to 1.00µg of scandium.

Solution prepared shall be timely transferred to a plastic bottle and be stored in

refrigerator at 0°C~4°C for 3 months.

9.11 Preparation of series standard solution. Respectively draw 0.0, 0.5, 3.0, 10.0 and

20.0 mL of boron standard working solutions (9.9); place into 100 mL volumetric flasks;

then accurately add 1.00 mL of yttrium element standard stock solution (9.7); use 5% nitric

acid solution to fix volume to scale; concentrations of solutions in volumetric flasks are

equivalent to 0.00, 0.05, 0.30, 1.00 and 2.00 µg of boron per milliliter. Solution prepared

shall be transferred to a plastic bottle timely.

Note. Yttrium element standard stock solution is not added to the standard solution tested

through ICP-MS.

When ICP-MS is adopted for determination, adopt yttrium standard working solution (9.10)

online internal standard adding.

10.1 All containers used in test are plastic.

10.2 Ultrapure water preparation system.

10.3 Sample smashing device.

10.4 Microwave digestion system.

10.5 Inductively coupled plasma atomic emission spectrometer (ICP-AES) and inductively

coupled plasma mass spectrometer (ICP-MS). All containers used have been soaked

overnight with 20% nitric acid.

11.1 Preparation of samples

There is a need to pay special attention to prevent all kinds of...

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