Abstract
The sample preparation of a cosmetic specimen in Cosmetic Science for the purpose of determining the analytical composition of heavy and toxic metals such as lead (Pb), mercury (Hg), cadmium (Cd), and arsenic (As) is of particular importance due to the difficulty of handling the sample. There are two main methods of sample preparation. The first method is the wet digestion of the sample with strong acids such as H2SO4, HNO3, HF, and HNO3/HCl (1:3) and the combination of a strong acid with H2O2. Liquid digestion of the sample under the influence of strong acids damages the organic material of the sample and converts the carbon into carbon dioxide. The contained metals are oxidized to the highest oxidizing step and converted to soluble salts. A problem with this method is the loss of metals during digestion because it occurs at high temperatures as well as the decrease in the concentration of the residual acid. The second method of preparation is the wet liquid digestion of the sample with strong acids in a microwave oven in a closed vessel. The acids that are used are mainly HNO3 or mixtures of acids such as HNO3–HCl and HNO3–H2SO4. When the sample in the acid’s solvent is exposed to microwave energy, it can reach temperatures substantially above the boiling temperature of the acid solution. The result is the decomposition of the organic material, the oxidation of the metals, and their conversion to soluble nitrates. The advantages of using microwaves are the ability to control the temperature, pressure, and loss of metals and, thus, avoid erroneous measurement results. Simultaneously with the above, extraction methods have been, for almost a decade, very effective complementary processes that we can use to enrich a sample of a cosmetic product. Liquid–liquid dispersion micro-extraction (DLLME) and solid phase extraction (SPE) are the two main methods used in sample preparation and are usually applied after the digestion process.
Highlights
This work is based on information obtained with the assistance of the ScienceDirect database and using keywords that refer to methods of pretreatment and the analysis of metals in cosmetic products
The aim of this review is to present and classify the methods for the pretreatment of cosmetic products with regard to heavy metals as well as to describe new pretreatment methods
In the above-described procedures, the digestions were done by treating each sample with nitric acid (HNO3) and hydrogen peroxide (H2O2) and the determination of the metal ions was achieved by flame atomic absorption spectrometry (FAAS)
Summary
This work is based on information obtained with the assistance of the ScienceDirect database and using keywords that refer to methods of pretreatment and the analysis of metals in cosmetic products. The amounts of Pd ranged from 6.4 μg g−1 to 22.4 μg g−1 Another mixture of nitric acid, hydrofluoric acid, and hydrogen peroxide (HNO3/HF/ H2O2) for the digestion of skin-whitening cosmetics and heavy metals determination was presented by Alqadami et al [14]. The combination of wet digestion and the use of microwaves allows for the degradation of the excipients of the cosmetic product and the dissolution of the metals This is achieved by taking a small amount of sample and a small amount of each strong acid, while the process is carried out at a higher speed to avoid partial or total loss of volatile compounds of heavy metals [18]. AAfftteerr tthhee pprroocceedduurree,, tthhee cclleeaarr ssoolluuttiioonn ooff tthhee rreessuullttiinngg ssaammppllee iiss ddiilluutteedd wwiitthh ddiissttiilllleedd wwaatteerr iinn aa vvoolluummeettrriicc flflaasskk ttoo bbeeccoommee tthhee fifinnaall ssoolluuttiioonn ooff uunnkknnoowwnn ccoonncceennttrraattiioonn
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