• Written by Gianpaolo Rota, Application Specialist | 17 May 2022

ISO 21392: a turning point in heavy metals analysis of cosmetic products

The new ISO 21392:2021 method

The new ISO 21392:2021 represents a turning point for laboratories that deal with cosmetic samples, because it univocally describes a method for quantification of trace levels of heavy metals in cosmetic products.
Came into effective in August 2021, the new ISO 21392:2021 is titled “Cosmetics — Analytical methods — Measurement of traces of heavy metals in cosmetic finished products using ICP/MS technique”. This document defines a universal method to determine the most common traces such as chromium, cobalt, arsenic, nickel, cadmium, antimony, and lead.
The new ISO 21392:2021 method can be defined as "self-supporting”. that is any knowledge or any use of other standards is not required at all, because all analytical procedures are specified directly in this ISO method and no consultation of other standards is required for its correct application. This simplifies al lot its adoption in analytical laboratories.
The main strengths of the described method are:
  1. The simultaneous and selective determination of all the cited metals is allowed.
  2. The appointed detection technique is mass spectrometry because of its low sensitivity: it allows to determine metal traces up to 20 μg / kg (º 0.02 ppm) or even lower with a standard configuration.

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Questions and Answers

Q1: We found that in some lipsticks a significant portion of the lead was contained in refractory compounds that required HF to enable a total assay. Therefore, this method may not be applicable for regulatory purposes if the regulation states the concentration of elements and not something like "acid extractable elements". We also found variable results as we varied the digestion conditions for samples with these refractory compounds.
We believe that results may vary in according to the digestion process. The main interest for heavy metals determination in cosmetics is correlated to safety reasons: metals that never will come into contact with the skin (that is, those ones linked in the crystalline lattice of inorganic materials) can be excluded from safety assessment.
Q2: If using a high pressure rotor, is it possible to reach higher pressure conditions compared the one recommended in the ISO 3696 (40 bar). Does this negatively affect the reaction or the recovery of analytes or is this a better approach? Would setting a higher pressure imply a method validation?
A higher performance rotor (or SRC reactor) cannot negatively affect the digestion process. The method suggests vessels that can hold pressures of 40 bar, so rotors that reach higher pressures are certainly fine. However, it is advisable to validate any analytical procedure, standard methods as well. As digestion procedures are not strictly mandatory, each lab must verify the recovery compliance.
Q3: In terms of price, which of the two devices (Rotor based vs. SRC) is more expensive?
SRC systems have a higher initial cost than rotor based units. Stated this, the high productivity and low number of consumables of the SRC reactor justify the difference in price. If you need more details about the price, please contact the local Milestone distributor in your country
Q4: I am using an SRC unit and I noticed if the concentration of some elements (for example Sn, Sb and Mo) is high, around 1000 ppb, the lost of them during the digestion is taking place. Any suggestion?
In this case I suggest an increase in the volume of hydrochloric acid. This should help with the dissolution of these elements in the liquid phase. I also suggest cooling the reactor to 60 ° C before releasing the internal pressure after the digestion cycle.
Q5: What is the maximum quantity of sample we can use for digestion in closed system?
Chpt. 8.2.2 and 8.2.3 provide good information: 200 mg as general case, up to 400 mg if sample contains a lot of water. Never less 100 mg, for homogeneity reasons.
If the ISO method is not considered, with high pressure rotors or SRC systems it is possible to increase the sample quantity up to 0.5 - 1 g depending on the reactivity of the sample
Q6: Your presentation states that ArCl is a potential interference for As. How can I avoid this problem?
The collision system of ICP/MS equipment should avoid the formation of adduct and interferences. We suggest you should vary the equipment settings to eliminate this problem. Verify it using a CRM
Q7: You were talking about how many samples we could run in 8 hours but don't we need to wash the tubes by a cleaning procedure before running another batch?
Yes, cleaning is necessary if you work with Teflon or quartz vessels / vials (although with quartz cleaning is faster and less frequent).
Considering the cleaning phase, the calculation gets worse and therefore the productivity is lower.
However, with SRC (with quartz or disposable glass vials) cleaning is minimal or not required and therefore the productivity gap between SRC and Rotor-based systems further increases
Q8: We have problems in determining arsenic, using the same microwave oven. Do you recommend me to use HCl or not? I use Ge as internal standard
I suggest using HCl. If the recovery is low the problem could be the digestion temperature. Some forms of Arsenates require high temperatures to be fully digested
Q9: Is an analysis on a sample sufficient to determine the dosage of heavy metals on the product or are multiple analyses recommended?
On our experience, one run of digestion is enough. Standard does not report the necessity of double digestion (chpt. 6,1 nd 8,2 of standard).
Double digestion run may be adopted with samples containing a lot of organic materials (typically, oils), but so not recurring in cosmetics
Q10: Is there any data available of heavy metal analysis using HF and without HF for cosmetic?
The repeatability studies during the development of the ISO 21392 did never include HF. So, no data are available.
Suggestion: some data may be found in scientific publication

Guidelines for sample preparation and analysis of cosmetics

Sample acid digestion was performed with two types of system based on different microwave technologies.
ETHOS UP

ETHOS UP

Microwave-assisted Rotor-based Digestion
The ETHOS UP is a flexible and high performing platform used for elemental analysis. Equipped with easyTEMP contactless sensor, it directly controls the temperature of all samples and solutions, providing accurate temperature feedback to ensure complete digestion in all vessels and high safety. ETHOS UP works with SK-15 rotor capable of high temperature (up to 300 °C) and pressure (up to 100 bar). The SK-15 also features Milestone’s patented “vent-and reseal” technology for controlling the internal pressure of each vessel. This ensures complete, safe and reproducible digestions of even the most diffi cult samples.
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ultraWAVE

ultraWAVE

Microwave-assisted SRC Digestion
The ultraWAVE, developed and patented by Milestone, with Single Reaction Chamber (SRC) technology utilizes high-performance stainless steel, allowing to reach higher pressures and temperatures (up to 199 bar and 300°C respectively) and to use any type of acids. Disposable vessels eliminate the need to assemble, disassemble or clean between processing. Just as important, dissimilar samples can be processed simultaneously using any mixture of disposable glass, quartz or TFM vials, thus saving time and money. The ultraWAVE is simply the fastest, easiest and most efficient digestion system ever made.
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Milestone Analytical
Milestone™ Srl
Via Fatebenefratelli 1/5 - 24010 Sorisole (BG) - Italy
Phone: +39 035.573857 | Fax: +39 035.575498
VAT n. IT01879330163
Privacy Policy
Cookies
Sitemap
Business Ethics & Compliance
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