Determination of Chromium Content in Hollow Capsules by Graphite Furnace Atomic Absorption Spectrosc

On 15 April 2012, CCTV's Weekly Quality Report programme, in its episode ‘Secrets Inside Capsules’, exposed certain enterprises in Hebei Province using quicklime to process leather waste into industrial gelatin. This gelatin was then sold to enterprises in Xinchang, Shaoxing, for manufacturing medicinal capsules. Ultimately, these capsules entered pharmaceutical companies and were ingested by patients. As leather processing involves chromium-containing tanning agents, such capsules frequently exceeded permissible chromium levels. Testing revealed that capsules used in 13 batches of medicines from certain pharmaceutical factories contained excessive chromium.

    As industrial gelatin primarily derives from leather products, and tanning constitutes the most critical stage in leather production, chrome tanning (primarily employing chromium oxide at approximately 12% concentration) has maintained its dominant position among tanning agents since its inception due to its superior tanning properties. Consequently, elevated chromium (Cr) levels are currently regarded as the primary distinguishing factor between industrial and edible gelatine.

The 2010 edition of China's Pharmacopoeia stipulates precise specifications for gelatin used in capsules, including gel strength, pH, light transmittance, electrical conductivity, sulphite content, peroxide value, loss on drying, ash residue, chromium content, heavy metal content, arsenic salts, and microbial limits. Currently, the state has exposed certain enterprises prioritising their own economic interests over public health and safety by producing gelatin from alum shale. Some hollow capsule manufacturers, driven by profit motives, utilise substandard gelatin as raw material and produce hollow capsules under extremely poor conditions. Glauber's salt contains substantial chromium that cannot be removed. Chromium exhibits significant toxicity to humans; low-concentration chromium in the environment causes subacute and chronic poisoning, while dust exposure leads to pneumonia, ulcers, lung cancer, and other diseases.

The 2010 edition of the Pharmacopoeia explicitly stipulates that chromium content in pharmaceutical gelatin must not exceed 2mg/kg.

Introduction to Chromium Content Evaluation Solutions for Pharmaceutical Hollow Capsules

  Reference to the 2010 edition of the Chinese Pharmacopoeia provides testing protocols for ‘chromium-toxic capsules’, intended for adoption by relevant industries. Comprehensive support is also offered to users regarding instrument after-sales service and technical applications, ensuring faster and more effective analytical testing.

1. Principal Instrumentation and Consumables 

Atomic Absorption Spectrophotometer AA1800H 

Nitric Acid              Grade A Pure              State Pharmaceutical Reagent 

Chromium Standard Material  1000 ppm              Non-Ferrous Metals Research Institute 

Ammonium Dihydrogen Phosphate  Grade A Pure              State Pharmaceutical Reagent 

2. Sample Preparation: 

Following the prescribed method in the 2010 edition of the Chinese Pharmacopoeia: Weigh approximately 0.5 g of empty capsules into a 100 mL PTFE digestion vessel. Add 5–10 mL concentrated nitric acid, mix thoroughly, secure the inner lid, and tighten the outer sleeve. Place in an electric heating oven for thermal digestion at 120–140°C. Following complete digestion, transfer the digestion vessel to an electric hotplate. Gradually heat at 120°C until reddish-brown vapour dissipates and the residue is nearly dry. Filter the precipitate, transfer the filtrate to a 25 mL plastic volumetric flask using 1% nitric acid, dilute to the mark, mix thoroughly, and proceed for analysis. Prepare blanks by the same method.

Instrumental Analysis Conditions:

Instrument Conditions:

Lamp Current: 4mA    Graphite Tube Type: Pyrolytic Coated

Wavelength: 357.9nm    Injection Volume: 20μl

Slit: 0.2nm    Matrix Modifier Injection Volume: 5μl

Ignition Mode: BGC-D2

Temperature Ramp Programme:

Graphite Furnace Temperature Programme (Pyrolytic Graphite Tube)

Stage #     Temperature (°C)   Time (sec)   Heating Mode   Sensitivity   Gas Line Type   Gas Flow (L/min)

1          150           30        RAMP      Low      Argon     0.3

2          250           15        RAMP      Low      Argon     0.3

3          350           10        RAMP      Low      Argon     0.7

4          400           10        RAMP      Low      Argon     0.7

5          550           5         RAMP      High      Argon     0.0

6         2200           3         STEP       High      Argon     0.0

7         2300           2         STEP       Low       Argon     1.0

Note: For chromium detection in pharmaceutical capsules, refer to the sample preparation method in food testing standard GB/T 5009.123-2003. The sample treatment methods include dry ashing and high-pressure digestion. The method described above employs high-pressure digestion, which offers advantages including rapid sample digestion, minimal contamination and loss, ease of operation, and accurate determination.