Why not use units of µg/g or µg/mL?
When performing elemental analysis most sample preparation and data workup is done in units of µg/g, µg/mL, µg/L, etc. However, when working with pharmaceutical samples the Permitted Daily Exposure (PDE) limits are reported in units of µg/day. Since different pharmaceutical products have different maximum dosages, it is critical to convert the conventional units used by elemental analysts into something that can be equated back to the PDE limit unit of µg/day. The J Value is used to perform this conversion.
What is a J Value?
If you are testing pharmaceutical samples using USP <232> / <233> and/or ICH Q3D, then you may be familiar with the concept of the J value. The J value is defined below:
PDE limits are determined by USP <232> and ICH Q3D, but the dilution factor and maximum daily dose is determined by you and your sample. The reason that the PDE limit is converted to a J value is to make it easier on the analyst after the sample has been diluted. A J value of 1 would be equal to the PDE limit.
How is the J Value calculated?
The PDE limit must be accurately accounted for based on the maximum daily dose (more or less sample per day, so think of this term as a separate dilution) and the digestion and/or dilution required to prepare your sample for analysis.
See an example below for calculating an oral J value for Cd in a sample that required a 0.4g to 100mL digestion and dilution (250X dilution) and the maximum daily dose is 1 g.
Example 1:
What happens if we keep the sample prep the same, but change the maximum daily dose to 5 g?
Example 2:
You can see that the J value decreases by a factor of 5. But how is this used in practice?
How is the J Value used in my method?
Under USP <233> your calibrations standards should range from 0.5 to 1.5 J, so you will need to know the dilution factor needed for sample preparation before preparing your calibration standards.
It is also important to consider that the elements you are testing for using USP <232> / <233> and ICH Q3D will ideally not be present in your sample, so you will follow a spike recovery method. USP <233> recommend spiking each sample with standard at a concentration ranging from 50% to 150% J for each element. So, if you spike your samples with a 100% J spike, you should expect a result for that sample to be around 100% J when ran against your calibration curve.
A low result against the calibration curve may be due to an issue of signal quenching which would require the use of an internal standard. Low results may also point to loss of sample during preparation, a common concern with some volatile elements like Hg and Os.
High results, greater than 150% spike recovery, would point to the presence of the analyte in your sample and further testing would be required.
How do I prepare standards in J Value concentrations?
Since the J value is tied so closely to your calibration standards and sample spike concentrations, the best method is to work with Certified Reference Materials (CRMs) that are already prepared at the listed PDE limit. This will allow you to calculate a dilution factor for your standards at 1 J by using the dilution factor of your sample multiplied by your maximum daily dose.
For example, a Cd CRM that is certified at 5 µg/mL would need a dilution factor of 250X to meet the 1 J concentration of 0.02 µg/mL as detailed in Example 1. Or the Cd CRM would require a dilution factor of 1250X to meet the 1 J concentration of 0.004 µg/mL in Example 2.
Inorganic Ventures offers a wide range of CRM products already prepared at concentrations to make working in concentrations of J Value easy!
Have additional questions? We’re here to help!
Check out our ICP Operations Guide and Trace Analysis Guide for more tips and tricks to achieve an accurate ICP analysis. Our team is ready to assist in all your analysis needs! Please send us an email or schedule a meeting to talk directly with a Technical Support Chemist.