1 Method Summary

Chromium is an essential trace element for the human body, and its deficiency or excess can cause serious harm to both humans and animals. Moderate chromium can increase the breakdown and excretion of cholesterol in the human body, and is an effective component of the glucose energy factor in the body. Lack of chromium can affect the metabolism of sugars and lipids, but excessive chromium can also pose a risk of cancer.

The determination of chromium is usually carried out by colorimetric method and atomic absorption spectroscopy. There are many interference factors in colorimetric method, and the operation is complicated; Atomic absorption spectroscopy has the advantages of easy operation, speed, and accuracy. This article refers to2010Annual edition of the Chinese Pharmacopoeia and food testing methodsGB-T5009.123-2003The determination of chromium in food "uses high-pressure digestion method, microwave digestion method, and wet method to process multiple user hollow capsule samples. After being tested by graphite furnace, the results of the three methods were compared and found to be very close, thus proving that all three methods are suitable for the detection of chromium in capsules.

2 Preparation of reagents and standard solutions required for the experiment

2.1 reagent

Nitric acid（HNO3）: Ultra clean and pure

Perchloric acid（HClO4）: Youji Pure

Chromium single element standard solution (Guo Family Reference Material Research Center)

2.2Standard solution preparation

2.2.1Preparation of chromium standard intermediate solution: suction100uLThe concentration is1000ug/mLThe chromium single element standard solution is placed in100mLIn a volumetric flask, add2mLNitric acid, diluted with deionized water to the mark, obtained a concentration of1Mg/mLChromium standard intermediate solution.

2.2.2Preparation of chromium standard curve: Draw the chromium standard intermediate solution prepared above0，0.25，0.50，0.75，1.00，1.50，2.50mLYu50mLIn a volumetric flask, add1mLNitric acid, diluted with deionized water, prepared0，5，10，15，20，30，50ng/mLSeries.

3 Instruments and working conditions required for the experiment

3.1Main Instruments

AA7003Atomic absorption spectrophotometer (equipped withCrHollow cathode lamp, Beijing Dongxi Analytical Instrument Co., Ltd

constant temperature drying oven

High pressure digestion tank(Nanjing Ruinike Technology)

Microwave digestion instrument(Nanjing Ruinike can provide microwave digestion tanks from various manufacturers)

electric hot plate

Adjustable electric furnace

3.2Instrument operating parameters

The working parameters of the instrument are as follows：

Watch1 Host measurement parameters

wavelength （λ/nm）	Lamp current （I/mA）	Deuterium lamp current（I/mA）	Spectral passband width (Δ λ)/nm）	Background subtraction
357.87	2	100	0.2	Deuterium lamp

Watch2furnace program

Id	Step Name	Initial temperature	Termination temperature	warm-up time	Internal air circuit	Auxiliary gas path	pattern
1	dry	40	80	30	open	Close	power
2	dry	80	120	10	open	Close	power
3	Ash	120	600	10	open	Close	power
4	Ash	600	600	8	open	Close	power
5	Ash	600	600	4	Close	Close	power
6	atomization	2600	2600	3	Close	Close	power
7	Clear	2800	2800	3	open	Close	power
8	cooling	0	0	30	open	Close	power

4 Analysis steps and results

4.1sample preparation

4.1.1microwave digestion method

Weigh out0.5gSample (accurate)0.0001g）Add an appropriate amount to the PTFE inner tankHNO3Gently shake well, soak overnight, cover the inner lid, tighten the outer jacket, and place it in a suitable microwave digestion device for digestion. After digestion, slowly heat the inner tank of the digestion tank on an electric heating plate until the reddish brown steam evaporates completely, and steam the solution until it is dissolved2～3mLLeft and right, remove, cool, use2% HNO3Clean and transfer in50mLIn a volumetric flask, use2% HNO3Dilute to the mark, shake well and set aside, while preparing the reagent Kong White.

4.1.2wet process

Accurately weigh0.5gSample (accurate)0.0001g）In the250mLAdd an appropriate amount to a high necked beakerHNO3 Add more0.5mLHClO4，Cover with a surface dish, place on an electric heating plate to digest and heat until white smoke appears. Add a small amount of water to remove excessHNO3，Wait for the liquid in the beaker to approach2～3mLWhen removing the cooling, use2% HNO3Clean and transfer in50mLIn a volumetric flask, use2% HNO3Dilute to the mark, shake well and set aside, while preparing the reagent Kong White.

4.1.3High-pressure digestion method

Weigh out0.5gSample (accurate)0.0001g）Add an appropriate amount to the PTFE inner tankHNO3Gently shake well, soak overnight, cover the inner lid, tighten the stainless steel jacket, and place it in a constant temperature drying oven130℃ digestion, after digestion *, cool to room temperature, place the digestion tank on an electric heating plate and slowly heat it until the reddish brown steam evaporates completely, and then steam the solution until2～3mLLeft and right, remove, cool, use2% HNO3Clean and transfer in50mLIn a volumetric flask, use2% HNO3Dilute to the mark, shake well and set aside, while preparing the reagent Kong White.

4.2determination

According to the working conditions of the instrument shown in the table above, the standard solution and sample solution were measured, and the injection volume was10ML.

4.3Result Calculation

X= (C－C0)×N×V×10-3／m

Where:

XThe chromium content in the sample, unit:Mg/g；

CThe chromium content in the digestion solution of the sample, unit:ng/mL；

C0The chromium content in the reagent Kong white liquid, unit:ng/mL；

NThe dilution ratio after sampling from the sample reserve solution;

VFixed volume, unit:mL；

mSample mass, unit:g.

The calculation result retains three significant digits.

4.4Standard Curve and Analysis Results (Example)

Cr curve equation: Curve equation: y=0.0135 * x-0.0018 Linear correlation coefficient: 0.99961

Watch3Add standard recycling test data

Pre-processing method	Sample solution contentng/mL	Add standard quantity ng/mL	Labeling test resultsng/mL	RSD%	Recovery rate（%）
microwave digestion method	12.3075	10	21.7333	1.37	94.25
wet process	13.6395	10	23.1704	1.19	95.31
High-pressure digestion method	12.0852	10	21.8815	1.43	97.96

5 Conclusion

5.1This article uses atomic absorption spectroscopy-Graphite furnace method（AAS）The high-pressure digestion method and wet method for determining chromium in hollow capsules have the advantages of simple equipment, easy and fast operation, and easy mastery. Customers can choose the appropriate pretreatment method according to their actual situation.

5.2 The detection limit of this experiment is:0.4pgRecovery rate:(94～97)%.

If dealing with opaque capsule samples, a small amount can be added dropwiseHFDissolve the residue, which has no effect on the results.

Notes:The nitric acid used in this experiment should beMOS）The container requirements are relatively high. Before processing the sample, a reagent should be prepared and tested on a white machine to verify its qualityCrIs the content low and able to meet the requirements of this experiment? Secondly, boil the utensils to be used with an appropriate amount of nitric acid for more than half an hour.

References：

• Analysis Method of Atomic Absorption Spectrometer

[2] Chinese Pharmacopoeia 2010edition

[3] GB-T5009.123-2003Food hygiene inspection methods Determination of Chromium in Food

[4] Kathryu J L,Steve J H,Microwave Digestion Procedures for Environment at Matrices[J],Anatyst ,1998,123(7):103133.

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