Determination of Lead in Food Additives by Graphite Furnace Atomic Absorption Spectrometry

Lead is mostly in the form of compounds in nature. The source of lead in food mainly depends on the following aspects: the existence of natural environment; the contamination of food by lead in the environment; the lead pollution of food processing; the lead to food in food containers and utensils. Pollution. Lead metabolism in the body, lead is absorbed by the small intestine, calcium, phytic acid and protein in the diet can hinder lead absorption; lead toxicity and harm to the human body, causing acute poisoning, hematopoietic damage, nervous system damage, kidney damage, immune system Damage, affecting bone metabolism, affecting endocrine, reproductive toxicity, embryo toxicity, teratogenic carcinogenesis.

Determination of lead in various foods by graphite furnace atomic absorption spectrometry

Instruments and equipment:

SDA-100FG flame/graphite furnace atomic absorption Spectrophotometer (Jinan Fine Measurement Technology Co., Ltd.), all functions are controlled by computer, and can be flexibly matched with flame and graphite furnace. Unique optomechanical design, safe and convenient flame system, advanced graphite furnace temperature control technology, optional background subtraction technology, and various convenient functions provided by the workstation, adapt to the pursuit of precision measurement automation.

Lead hollow cathode lamp .

Sample pretreatment:

During the sampling and preparation process, care should be taken not to contaminate the sample.

After the grain and beans are removed, they are ground, passed through a 20 mesh sieve, stored in a plastic bottle, and stored for later use.

Fresh samples with high moisture content such as vegetables, fruits, fish, meat and eggs are homogenized by a food processor or a Homogenizer, stored in plastic bottles, and stored for future use.

Sample digestion (can be digested according to laboratory conditions using any of the following methods):

1. Pressure digestion tank digestion method: Weigh 1g ~ 2g sample (accurate to 0.001g, dry sample, high fat sample <1g, fresh sample <2g or press the pressure digestion tank instruction manual to weigh the sample) Teflon inner tank, soaked in 2mL ~ 4mL of nitric acid overnight. Add 2 mL to 3 mL of hydrogen peroxide (the total amount cannot exceed 1/3 of the tank volume). Cover the inner cover, tighten the stainless steel jacket, put it into a constant temperature drying oven, keep it at 120 °C ~ 140 °C for 3h ~ 4h, naturally cool to room temperature in the box, wash or filter the digestive juice with a dropper (depending on the digestion test) Depending on the salt content), in a 10mL ~ 25mL volumetric flask, wash the canister several times with water, wash the solution into a volumetric flask and dilute to volume, mix and set aside;

2. Dry ashing: Weigh 1g ~ 5g sample (accurate to 0.001g, according to lead content) in porcelain crucible, first small heat on the adjustable electric heating plate carbonized to smokeless, moved into the muffle furnace 500 It was ashed at °C±25°C for 6h～8h and cooled. If the individual samples are not completely ashed, add 1 mL of mixed acid to heat on a tunable electric furnace for a small heat until repeated digestion, let cool, dissolve the ash with nitric acid, and wash the sample digest with a dropper. Filter into (depending on the salt of the sample after digestion) 10mL ~ 25mL volumetric flask, wash the porcelain mash several times with water, wash the liquid into the volumetric flask and dilute to the mark, mix and reserve; at the same time as reagent blank.

3. Ammonium persulfate ashing method: Weigh 1g ~ 5g sample (accurate to 0.001g) in porcelain crucible, add 2mL ~ 4mL nitric acid soak for more than 1h, first small charring, add 2.00g ~ 3.00g after cooling Ammonium sulphate is placed on top, continue to carbonize to no smoke, transfer to muffle furnace, constant temperature at 500 °C ± 25 °C for 2 h, then rise to 800 ° C, keep for 20 min, cool, add 2 mL ~ 3 mL of nitric acid, use a dropper to sample Wash or filter the digestive juice (depending on the salt content of the sample after digestion) in a 10mL ~ 25mL volumetric flask, wash the porcelain mash several times with water, wash the liquid into a volumetric flask and dilute to volume, mix and set aside; At the same time, the reagent is blank.

4 Wet digestion method: Weigh 1g ~ 5g (accurate to 0.001g) in a conical flask or a high-beast beaker, put a few glass beads, add 10mL mixed acid, cover and soak overnight, add a small funnel to the electric furnace On the upper digestion, if it turns brownish black, add acid, until white smoke, the digestive juice is colorless transparent or slightly yellow, let cool, use the pipette to wash or filter the sample digestive juice (depending on the digestion test) Depending on the salt content) In a 10mL ~ 25mL volumetric flask, wash the conical flask or high-beat beaker several times with water, wash the mixture into a volumetric flask and dilute to volume, mix and set aside;

Instrument reference conditions:

Wavelength 283.3nm,

Slot 0.2nm to 1.0nm,

Lamp current 5mA ~ 7mA,

Drying temperature 120 ° C, 20 s;

Ashing temperature 450 ° C, lasting 15s ~ 20s,

The atomization temperature is 1700 ° C ~ 2300 ° C, lasting 4s ~ 5s,

The background correction is a xenon lamp or a Zeeman effect.