Spectrophotometric Determination of Lead - Pharmaceutical Technology

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Spectrophotometric Determination of Lead
The authors developed a reliable spectrophotometric method for determining and measuring trace amounts of lead in various samples.

Pharmaceutical Technology

In this reported method, dithizone extraction solution was washed with 1% HCl rather than 1% of HNO3 as in the USP method (24) because a trace amount of HNO3 left in the dithizone solution could rapidly decompose the dithizone. After replacing 1% of HNO3 with 1% of HCl, the decomposition problem did not happen again.

To maximally reduce the consumption of chloroform, some preliminary experiments were performed for the recycling of the dithizone chloroform solution. We found the following procedure could be used for recycling the dithizone chloroform solution: After lead extraction, the 0.003% dithizone solution is washed with 20 mL of DI water, followed by 20 mL of 1% of HC, and then washed again with 20 mL of DI water. After washing, a small amount of ethanol is added into the dithizone solution, 1 mL to 100 mL (1:100 v/v), to stabilize the dithizone. This solution should be kept in a refrigerator until next time of use. Based on our experimental results, the dithizone solution could be reused for as many as 10 times, as long as the greenish-blue color retains stable.


This method was used in our quality control laboratory for several months with various samples and proved to be reliable for the determination of trace amounts of lead in all samples. From sample digestion to interfering element masking and to dithizone chloroform solution recycling, each step has been optimized. For certain mixture samples of organic ingredients and minerals, repeated treatment with H2SO4–H2O2 and H2SO4–HNO3 is very effective and could reduce the digestion time dramatically. For the determination of ppm levels of lead in salts of alkaline earth metals, sulfuric acid should be avoided and an extra amount of citrate reagent should be used to prevent the precipitation. Recycling the dithizone solution can not only reduce the consumption of chloroform but also maximally lower the overall cost. This method is very rugged and could be used for routine analysis of trace amounts of lead as well as for the validation of other instrumental methods such as ICP-MS or GFAA.

Lang Lang is a senior student at School of Pharmacy & Allied Health Science, University of Montana, Missoula, MT. Konghwa Chiu is a professor in the department of applied science, National Hualien University of Education, Taiwan, ROC. Qingyong Lang* is a senior analytical chemist in the R&D department at Nutritional Laboratories International, Missoula, MT,

*To whom all correspondence should be addressed.

Submitted: Aug. 21, 2007. Accepted: Dec.3, 2007


1. R. Eisler, "Lead Hazards to Fish, Wildlife, and Invertebrates: A Synoptic Review," Biological Report 85(1.14), Contaminant Hazard Reviews, US Fish and Wildlife Service (1988), available at http://www.pwrc.usgs.gov/infobase/eisler/CHR_14_Lead.pdf, accessed March 7, 2008.

2. C. Rubio et al., "Lead Dietary Intake in Spanish Population (Canary Islands)" J. Agric. Food Chem. 53 (16), 6543–6549 (2005).

3. D. K. Houston and M. A. Johnson, "Blood Lead Level is Associated with Elevated Blood Pressure in Blacks," Nutr. Rev. 57 (9 Part 1), 277–279 (1999).

4. California Poison Control System, "Lead Poisoning," available at http://www.calpoison.org/public/lead.html.

5. FDA, 21 CFR Part 173 "Secondary Direct Food Additives Permitted in Food for Human Consumption," (2002), available at http://a257.g.akamaitech.net/7/257/2422/14mar20010800/edocket.access.gpo.gov/cfr_2002/aprqtr/21cfr173.60.htm, accessed Mar. 7, 2008.


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