Sample Preparation for Elemental

Impurities

Nikki Schopp, 3/19/14

SGS Life Science Services

Overview of Methods

• Heavy Metals testing, currently performed per USP <231>

– established over 100 years ago – undergoing a much needed update – toxicological data is being used to establish limits – Both toxic metals and metals used in processing are being

addressed.

• Elemental Impurities – USP <232>,<233> & <2032>;ICH Q3D (Draft) – USP, EP and ICH all expressed desire to be harmonized prior to

implementation – Both metals addressed and limits are concerns.

Getting Started

• When analyzing for trace metals using Inductively Coupled Plasma (ICP), sample preparation is critical.

– The solubility of the test article is crucial, but not the primary factor when choosing a sample preparation method.

Sample Preparation Options

Four sample preparation methods are typically used when performing Elemental Impurities testing.

• Neat

• In aqueous solutions

• In organic solutions

• Digested in a closed-vessel apparatus

Standard Preparation

• The blank and standard solutions should be prepared in the same matrix as the sample,

– solvent, acid concentration and stabilizers

• Spike recovery studies need to be performed

– Ensures method accuracy, specificity and precision when used as a quantitative method.

• Recommended Stabilizing Acids

– Hydrochloric Acid- Osmium and Ruthenium

– Nitric Acid – Cd, Pb, Hg, As, In, Cr, Ni and Cu

– Nitric Acid/Hydrochloric Mixture- Pd, Pt, Rh, V

– Hydrofluoric – Molybdenum

• Other stabilizers – Gold for Hg

Choosing a Diluent (1)

Choosing a Diluent (2)

• Samples analyzed neat – choose a diluent for standards

• Samples diluted in an acid – correct acid and concentration needs to be chosen

• Consideration: Just because a test article is water soluble does not mean that the direct aqueous solution method is the best choice

Choosing a Diluent (3)

• Organic solvents are not the easiest to run on ICP (spray chamber, nebulizer, instrument settings)

• MeOH, EtOH, Chloroform

• Concentration of organic solvent

Microwave digestion

• Choosing the correct acid and heat profile

• Interferences

• Determing the proper mixture of acids to obtain stability and recovery (i.e. Os)

Validation Requirements

• Accuracy – average % Recoveries must be – 70-150% at the limit – half the limit – 1.5x the limit

• Precision – %RSD of calculated concentration NMT 20%

• Ruggedness (Intermediate Precision) – two analyst – 3 different days – %RSD of calculated concentration NMT 25%

Case Study I – Direct Aqueous

• Injectable Drug Product- 3 different sample preparations were needed

• Solution 1 – 2% Nitric Acid Diluent for As, Hg, Ru, Cd, Pb, Cr, Mo, Pd and V

• Solution 2 – 12% Nitric/8% Hydrochloric acid for Ni, Cu, Ir, Pt, Rh

• Solution 3 – 2% Hydrochloric acid for Osmium

Case Study I (2)

• Test Solution 1 weigh and dilute – with all injectables this is the first attempt during development. As, Hg, Ru, Cd, Pb, Cr, Mo, Pd and V all met requirements

• Elements that did not meet requirements

Level Ni Cu Rh Os Ir Pt

50% 63 58 59 62 59 65

100% 66 62 61 66 62 69

150% 66 61 56 62 59 66

Case Study I (3)

• Test solution 2 used microwave digestion

Remaining elements passed requirements, except Os

• Test Solution 3 weigh and dilute, different acid- since Os is known to behave better with HCl, this was used as the diluent for Os.

Materials used for Development vs. Validation

• Development and validation should be done on the final stage of the material of interest

• Changing the process of manufacturing and purification of the material of interest can change recoveries, especially if acids and/or bases are used in the purification process

• Development done on a material, all requirements are met, then validation begins on a purified product, some recoveries did not meet

Case Study II

• Development done on unpurified material – sample preparation was weigh and dilute, all criteria

were met

• Validation performed on purified material

• All recoveries were met except for Palladium

-50% the limit average = 65%

-100% the limit average= 67%

-150% the limit= 66%

Case Study II (2)

• Purification of the material inhibited the Palladium from being recovered

• Currently in the process of re-developing a method

Case Study III

• Development sample preparation on unpurified material – nitric acid, hydrogen peroxide heat in oven at 105°C

• All recoveries meet criteria during development

• Validation on purified material-all elements meet criteria except Palladium

50% limit avg recovery= 50.1%

100% limit avg recovery= 82.1%

150% limit avg recovery= 89.5%

Case Study III (2)

• Re-developed the method using microwave digestion

• All Elements meet criteria, even Palladium

Pd 50% limit avg recovery= 101%

Pd 100% limit avg recovery= 103%

Pd 150% limit avg recovery= 99%

Summary

• USP will not be giving specific sample preparations in the monograph

• Sample Preparation for Elemental impurities will need to be determined on a case by case basis

• Solubility plays a role however, it is not the final step in determining a sample preparation

Contact Information

• Nikki Schopp, Team Leader Analytical Services, Life Science Services, SGS

• Nikki.Schopp@SGS.com

• 616 Heathrow Dr. Lincolnshire IL 60069

• (847) 821-8900