التطبيقات

Determination of Chromium in Wheel Hub Surface Paint (Flame Atomic Absorption Spectrometry)

سبتمبر 9, 2025

1. Method Overview

The wheel hub is cleaned with purified water, dried, and its surface topcoat, coating paint, and primer are scraped off with a scraper. Microwave digestion is adopted, and the concentration of chromium is determined by flame atomic absorption spectrometry at a wavelength of 357.9 nm.

2. Instruments and Reagents

2.1 Instruments and Equipment

2.1.1 Testing Instruments

اسم	كمية	Technical Requirements	مُكَمِّلات
Microwave Digestion System	1 set	Equipped with platinum resistance and infrared temperature measurement; temperature control accuracy: ±0.1℃	–
Temperature-Controlled Hot Plate	1 set	–	–
Electronic Balance	1 set	Sensitivity: 0.1 mg	–

2.1.2 Sample Pretreatment Equipment

Serial No.	اسم	كمية	Technical Requirements	مُكَمِّلات
1	Temperature-Controlled Hot Plate	1 set	–	–
–	Volumetric Flask; Colorimetric Tube	–	–	–

2.2 Reagents

2.2.1 Raw Reagents

（No specific raw reagents listed in the original document except for the prepared reagents below）

2.2.2 Prepared Reagents

اسم	Preparation Method
Nitric Acid Solution (1+99)	Measure 10 mL of nitric acid, slowly add it to 990 mL of deionized water, and mix well.
Ammonium Chloride Solution (40 g/L)	Weigh 4 g of ammonium chloride, dissolve it in deionized water, and mix well.

2.3 Reference Standards

2.3.1 Stock Solution

Serial No.	اسم	Technical Requirements	ملاحظات
1	National Liquid Reference Material – Chromium	GSB 04-1723-2004 (a); Concentration: 1000 μg/mL	Provided by National Center for Analysis and Testing of Nonferrous Metals and Electronic Materials

3. Operation Procedure

3.1 Sample Preparation

3.1.1 Preparation of Test Solution

Sample Pretreatment: Clean the automobile wheel hub with purified water, dry it, and scrape off the surface topcoat, coating paint, and primer with a scraper. Weigh 0.2 g of the sample (on an electronic balance) into a polytetrafluoroethylene (PTFE) digestion tank, add 7 mL of nitric acid and 2 mL of hydrogen peroxide, cover the digestion tank, and place it in the microwave digestion system for digestion. After digestion, cool the tank, take it out, and place it on a temperature-controlled hot plate for acid driving at 160℃ until the solution volume is reduced to approximately 1 mL. Transfer the solution to a 25 mL colorimetric tube with deionized water, dilute to the marked volume with deionized water, shake well, and set aside for testing.

Microwave Heating Program

Step	Temperature (℃)	Holding Time (min)
1	–	3
2	130	3
3	150	3
4	170	–
5	–	–

Note: If there is a small amount of flocculent insoluble matter in the digested sample, filter it through a 0.45 μm filter membrane before testing on the instrument.

3.1.2 Preparation of Standard Solutions

Preparation of Chromium Standard Series:
Accurately pipette 0.0 mL, 0.1 mL, 0.2 mL, and 0.3 mL of chromium standard stock solution (1000 μg/mL) into 100 mL volumetric flasks respectively. Add 5 mL of 40 g/L ammonium chloride solution to each flask, dilute to the marked volume with nitric acid solution (1+99), and obtain chromium standard series solutions with concentrations of 0.0 μg/mL, 1.0 μg/mL, 2.0 μg/mL, and 3.0 μg/mL.

3.2 Sample Testing

Testing Conditions
Reference Conditions for Flame Atomic Absorption Spectrophotometer Detection

Wavelength (nm)	Slit Width	Lamp Current (mA)	Gas Flow Rate	Background Correction
357.9	0.22	8	2500	None
(Supplementary Parameter)	4.0	–	–	–

اختبار العينة
Adjust the instrument to the optimal working state, ignite the flame, adjust the fuel gas flow rate, test the blank solution, standard series solutions, and sample solutions in sequence, read the data, input the sample weight, and check and record the results.