Spectrophotometric Determination of Lead - Pharmaceutical Technology

Latest Issue
PharmTech

Latest Issue
PharmTech Europe

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


Pharmaceutical Technology


Step 6. Add 10 mL of DI water to the sample beaker and stir to dissolve any water-soluble salt. Add 5 mL of 30% ammonium citrate solution, 2 mL of 20% hydroxylamine hydrochloride solution, and mix well. (Note: For alkaline earth-salt samples, do not add the 10 mL of DI water, instead add 20 mL of 30% ammonium citrate and 2 mL of 20% hydroxylamine hydrochloride solution, and mix well.)

Step 7. Add two drops of 0.1% phenol red in ethanol. Carefully adjust the pH with ammonium hydroxide until the solution changes colors from pink to yellow then back to pink again. Cool the solution to room temperature. Completely transfer the sample to a 125-mL separatory funnel for liquid–liquid extraction of the lead.

Step 8. Into the separatory funnel containing the sample solution, add 2 mL of 5% potassium cyanide solution and 5 mL of 0.003% dithizone extraction solution. Shake the separatory funnel for ~30 s, carefully releasing pressure from time to time. Drain the bottom dithizone phase to a 60-mL separatory funnel containing 20 mL of 1% HCl, which is used for back extraction of lead.

Repeat the extraction three more times. Collect all the dithizone phases in the 60-mL separatory funnel. The original aqueous sample solution should be collected in a specific container for waste treatment.

Step 9. Shake the 60-mL separator funnel for 45 s to back-extract lead to the acidic aqueous phase. Drain the dithizone phase into a beaker containing 20 mL of DI water to recycle the dithizone solution.

Step 10. In the 60-mL separatory funnel, add 4 mL of 2% ammonium cyanide and 5 mL of 0.001% standard dithizone solution. Shake the separatory funnel for 45 s. Drain the dithizone solution into a 10-mL of centrifuge tube for the spectrophotometric determination of lead.

Step 11. To construct the standard calibration curve, extract lead standard solutions containing 0.0, 1.0, 5.0, 10.0, and 25 μg of lead in the same way as described in steps 6–10. Using chloroform as a reference, measure the absorbances of the solutions at 520 nm. Create a calibration curve from the measured results. The R 2 value should be .0.990.

Step 12. Measure the absorbance of the samples at 520 nm. Calculate the lead concentration based on the standard calibration curve obtained at Step 11.

For quality assurance, we performed triplicate analyses for all samples.

Results and discussion

Method validation. The method was validated using two means: standard addition or method recovery and comparison with an accepted ICP-MS method.


Table I: Lead recovery test results (n 5 3).
Method recovery results. Two samples with nondetectable lead were specifically chosen for lead recovery testing. These samples were spiked with 0.5 –3.0 μg of lead, and triplicate analyses were performed in the same manner as for the regular samples. Table I lists the lead recovery test results. In these tests, 10 g of dried hotdog bun powder and 2 g of green tea extract were used.


ADVERTISEMENT

blog comments powered by Disqus
LCGC E-mail Newsletters

Subscribe: Click to learn more about the newsletter
| Weekly
| Monthly
|Monthly
| Weekly

Survey
FDASIA was signed into law two years ago. Where has the most progress been made in implementation?
Reducing drug shortages
Breakthrough designations
Protecting the supply chain
Expedited reviews of drug submissions
More stakeholder involvement
Reducing drug shortages
70%
Breakthrough designations
4%
Protecting the supply chain
17%
Expedited reviews of drug submissions
2%
More stakeholder involvement
7%
View Results
Eric Langerr Outsourcing Outlook Eric LangerTargeting Different Off-Shore Destinations
Cynthia Challener, PhD Ingredients Insider Cynthia ChallenerAsymmetric Synthesis Continues to Advance
Jill Wechsler Regulatory Watch Jill Wechsler Data Integrity Key to GMP Compliance
Sean Milmo European Regulatory WatchSean MilmoExtending the Scope of Pharmacovigilance Comes at a Price
From Generics to Supergenerics
CMOs and the Track-and-Trace Race: Are You Engaged Yet?
Ebola Outbreak Raises Ethical Issues
Better Comms Means a Fitter Future for Pharma, Part 2: Realizing the Benefits of Unified Communications
Better Comms Means a Fitter Future for Pharma, Part 1: Challenges and Changes
Source: Pharmaceutical Technology,
Click here