Soil, food, and water quality are gradually polluted by industrial waste gas, wastewater, and waste residue. Some people even directly use industrial wastewater to irrigate crops, causing a large accumulation of heavy metals such as cadmium, copper, arsenic, chromium, mercury, nickel, aluminum, fluorine, titanium, selenium, iron, zinc, manganese, and copper in the soil tillage layer, especially in urban suburbs where the phenomenon is more serious; In addition, the extensive use of inorganic chemical pesticides has led to serious exceedance of heavy metal content in vegetables and fish, continuously accumulating in the human body, resulting in chronic heavy metal poisoning among consumers. There have been multiple incidents of collective heavy metal poisoning in China, which have attracted high attention from the government and various sectors of society. However, the current heavy metal determination methods have slow determination speed, complicated steps, and expensive instruments. Based on this situation, we have developed a rapid determination method for heavy metals, which can be used for rapid combined determination of lead, arsenic, chromium, cadmium, mercury, etc. in samples such as vegetables, food, soil, organic fertilizers, and tobacco leaves.

1、 Detection principle of soil heavy metal detector:

（1） After digestion of the sample, all forms of heavy metals (including arsenic, lead, cadmium, chromium, mercury, nickel, aluminum, fluorine, titanium, selenium, iron, zinc, manganese, copper, etc.) are converted into ionic forms. After adding relevant detection reagents, the color appears. Within a certain concentration range, the depth of the solution color is proportional to the content of heavy metals, following the Lambert Beer law. The content value is then determined by instruments and compared with the national standard for the safety and quality of agricultural products and the allowable limit for pollution-free vegetable safety requirements to determine the content of heavy metals in vegetable samples.

（2） Detection principles and standards for various heavy metals

1. The detection principle and adopted standards of heavy metal arsenic

Adopting the national standard (GB/T50091.1-2003) borohydride reduction colorimetric method, the sample is digested, potassium iodide thiourea is added and heated to reduce pentavalent arsenic to trivalent arsenic. Under acidic conditions, potassium borohydride reduces trivalent arsenic to negative trivalent, forming arsine, which is introduced into the absorption solution and appears yellow. The arsenic content is detected by the instrument.

2. The detection principle and adopted standards of heavy metal lead

The national standard (GB/T5009.12-2003) dithizone colorimetric method is adopted, which means that after digestion of the sample, under weakly alkaline conditions, lead ions form a red complex with dithizone, dissolve in chloroform, and perform colorimetric determination.

3. The detection principle and adopted standards of heavy metal chromium

After digestion of the sample, in the presence of divalent manganese, chromium ions react with diphenylcarbazide to form a purple red complex. The color of the complex is directly proportional to the hexavalent chromium content, and the chromium content can be determined by colorimetric analysis.

4. The detection principle and adopted standards of heavy metal cadmium

Using the national standard (GB/T5009.15-2003) colorimetric method, after digestion of the sample, under alkaline conditions, cadmium ions react with 6-bromophenylthiazolylazo naphthol to form a red complex, which is dissolved in chloroform for colorimetric determination.

5. The detection principle and adopted standards of heavy metal mercury

Using the national standard (GB/T5009.17-2003) dithizone colorimetric method, after digestion of the sample, under acidic conditions, mercury ions react with dithizone to form an orange red complex, which is dissolved in chloroform,Colorimetric measurement.

2、 Testing process

Refer to the user manual

3、 Instrument technical specifications

1. Instrument transmittance accuracy ≥ ± 0.5%

2. Instrument repeatability ≤± 0.05%

3. Instrument stability without drift/30 minutes (after preheating the instrument for 5 minutes)

4. Linear error ≤ 0.2% (0.002, copper sulfate detection)

5. Instrument power consumption ≤ 5W

6. Power supply AC220V/50Hz or DC12V

7. The built-in thermal printer can automatically print out the detection results, which is convenient and intuitive.

4、 Instrument measurement items

1. Instrument measurement items

Determination of heavy metals (lead, arsenic, chromium, cadmium, mercury, nickel, aluminum, fluoride, titanium, selenium, iron, zinc, manganese, copper) in soil, fertilizers, food, vegetables, and fruits.

2. Instrument expansion testing project

The instrument can be extended to measure the nutrient content of soil and fertilizers.

5、 Instrument testing characteristics

1. The performance is reliable, and the working stability is 5-6 times better than the national standard JJG79-90. The repeatability reaches the index of grating spectrophotometers. It adopts microprocessor technology, microcontroller control, touch buttons, and is easy to operate.

2. The heavy metal testing adopts joint digestion and sub item testing techniques, simplifying the testing process, reducing testing time, greatly improving testing efficiency, and enhancing testing accuracy.

3. Strong scalability, this instrument can not only be used for heavy metal detection but also for testing nutrients in soil, fertilizers, and plants, making it versatile.

4. The soil heavy metal detector integrates medicine, equipment, and instruments into one, equivalent to a small laboratory with two aluminum alloy boxes, easy to carry, convenient for on-site testing, and mobile service. Suitable for grassroots testing departments to screen vegetables, fruits, and other foods containing heavy metal pollution.

Instrument configuration list

Instrument box and medicine box

Number Name Quantity Number Name Quantity

01 Host (built-in printer) 1 unit 01 Soil heavy metal reagent 1 set/100 times

02 electronic balance (100g/0.01g) 1 set 02 triangular bottle 100ml 2 pieces

03 Color dishes 4 pieces 03 Volumetric flask 1 piece

04 Scale Straws 1, 5, 10mL each 1 bottle 04 Washing Bottle 1 bottle

2 fuses 05, 1 set of sample spoon 05

06 Host power cord 1 piece 06 Qualitative filter paper 1 box

07 DC 12V wire 1 piece 07 suction ball 1 piece

08 instruction manual, certificate of conformity 1 set 08 small aluminum box 1

09 09 Measuring cylinder (50mL) 1 piece

30 10 10ml centrifuge tubes

11. 1 centrifugal tube rack