April 10, 2007
Dr. Catherine Sheehan, Director,
Excipients and Food Chemical Codex,
Division of Standards Development, USP
Email: cxs@usp.org
I am writing you as Director of Technical and Regulatory Affairs, Salt Institute. This communication refers to the Food Chemicals Codex: Last Call for Revision Requests.
Specifically I refer to the Food Chemicals Codex V request on page 408 that the “manufacturers are encouraged to develop and validate methods to use in industrial settings and that are sensitive enough to detect lead in the amounts typically present in sodium chloride, and to propose such methods to the committee in a timely manner.”
The Salt Institute Food Issues Working Group maintains that the current test of Heavy Metals (as Pb) currently listed remains the most reliable, economical, and feasible for a salt plant environment. We respectfully reiterate our objections in more detail. We also would like to recommend a method to be used should a lead-specific method become a requirement. This method could serve the need for potassium chloride as well.
These comments were originally sent into Dr. Ricardo Molins on April 23, 2004. As he is no longer affiliated with the Institute of Medicine, I send these comments to your attention.
Proposed Methods (pp. 762-766, FCC IV)
Sample Preparation.
The first and biggest problem is that sample preparation suggested in the FCC IV will not work for a salt sample. We have repeatedly tried to use the sample preparation method and it is not workable. This procedure (pp. 762-766, FCC IV) was obviously written for organic matrices where wet ashing with sulfuric acid is a means of concentrating a relatively large sample into a small amount of ash. This will not work with sodium or potassium chloride. For these compounds, adding sulfuric acid and heating will only result in a messy mixture and will not reduce the salt to an ash. It will be impossible to re-dissolve the 10 g sample in a small amount (10 mL) of water. Also, with any preparation method, the more the sample is handled (ashing, transferring, etc.), the higher the risk there is for loss of lead or contamination.
This digestion procedure is labor intensive and unnecessary for salt or potassium chloride. It was also written for organic matrices. To quantify the lead, you would have to make up standards in the same salt matrix or pre-extracted brine and carry through the entire extraction procedure. Furthermore, the procedure calls for use of potassium cyanide and extracting the lead into chloroform. In order to conform with Good Laboratory Practices, salt companies have either eliminated or restricted usage of these materials in our laboratories. Chloroform is a suspected carcinogen and has exhibited teratogenic activity in animals. Because of the foregoing, we have not tested this method and therefore it is unknown if the method is suitable for determining a lead (Pb) limit of 2 mg/kg in salt or potassium chloride.
Flame AA is not sensitive enough for this test; the detection limit is too close to the lead limit. Many laboratories are replacing Atomic Absorption with Inductively Coupled Plasma Emission Spectroscopy or ICP. The sensitivity and speed of ICP is much higher and the cost difference between AA and ICP is decreasing. Another advantage of ICP is that it does not require an electrode-less discharge lamp for each element of interest, e.g. lead.
Again, many labs are replacing GFAA with ICP. Analysis by ICP is much faster and less prone to matrix problems. Salt, especially, can cause some major problems with GFAA and most likely the “method of addition” would have to be employed for calibration. If the lab technician is not sufficiently skilled or careful with either matrix matching or method of addition, it can lead to erroneous results.
This method also calls for use of chloroform. Extractions are very time-consuming and extra care must be taken to avoid contamination of the sample. Standards have to be made, either from pre-extracted brine or by using an “ultra pure” salt to prepare a calibration curve. This is also very time-consuming, labor intensive, and therefore expensive. This method specifies Flame AA as the means of detection, which may be a problem in the future, as AA’s are replaced with more convenient ICP units.
Therefore, the Salt Institute and its member salt companies proposes the following method:
FCC Lead-Specific Method—Salt Institute Guideline for Salt.
The salt industry opposes the deletion of the “heavy metals as lead” test. It is a quick pass/fail test that has and continues to serve the food industry well. It is consistent with the USP consideration of this issue. It shows that food-grade salt is well below the 2 mg/kg limit not only for lead but for other heavy metals as well. Nevertheless, after much consternation concerning future FCC actions in this regard, we believe that this attached proposed lead-specific method will serve as the best alternative should the FCC Committee mandate a lead-specific method for food-grade salt (sodium chloride) and potassium chloride. An explanation of the reasoning behind the proposal for adoption of this particular method follows:
The proposed method utilizes ICP instrumentation. ICP is faster and much more sensitive than Flame AA. Aside from the fact that Flame AA is not sensitive enough for the lead test, with a single scan, ICP can provide analysis for a wide variety of elements at the same time, including lead, whereas Flame AA requires a specific electrodeless discharge lamp for each element. Therefore, Flame AA requires multiple runs, each with an appropriate lamp, to obtain an assay of other heavy metals that may also be of interest. This is important since our customers are, to an increasing degree, asking for analysis for other metals (e.g. arsenic, barium, cadmium, silver, etc.) including lead.
ICP Emission may not be quite as sensitive as Graphite Furnace Atomic Absorption (GFAA) but it does not have the inherent sample matrix problems that make GFAA extremely labor intensive.
As stated previously, the speed and sensitivity of ICP is much higher and the cost differential between Flame AA and ICP is decreasing.
The proposed method employs a very simple digestion procedure using aqua regia with minimal handling to avoid lead loss or contamination. Only two calibration steps are required and the sample is read directly.
We are still of the one-mind belief that past historical data supports the use of a Heavy Metals as Lead pass/fail test since the lead levels are so low not to be an issue for testing. As you are aware, the USP monograph for Sodium Chloride specifies the heavy metals as lead test rather than a lead-specific test. It is quick, inexpensive, yet provides sufficient sensitivity for determination of a 2 mg Pb/kg limit in salt (NaCl) and potassium chloride (KCl).
Currently none of the Salt Institute member salt companies have an ICP spectrophotometer. A proposed lead-specific method that has been given limited salt industry approval. Should the Committee decide to require a lead-specific method, we offer this method as the best option.
Sincerely,
Morton Satin
Director of technical and Regulatory Affairs
Salt Institute
700 N. Fairfax Street
Suite 600
Alexandria, VA 22314
Phone: 703-549-4648
Fax: 703-548-2194
Email: morton@saltinstitute.org
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