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Isothiazolinones Quantification in Shampoo Matrices: A Matter of Method Optimization or Stability Driven by Interactions?

1
CICS-UBI, Health Sciences Research Center, Faculty of Health Sciences, University of Beira Interior, Avenida Infante D. Henrique, 6200-506 Covilhã, Portugal
2
Labfit–HPRD Health Products Research and Development, Lda Edifício UBIMedical, Estrada Municipal 506, 6200-281 Covilhã, Portugal
3
CNC.IBILI–Center for Neurosciences and Cell Biology, University of Coimbra, 3004-531 Coimbra, Portugal
*
Author to whom correspondence should be addressed.
Cosmetics 2020, 7(1), 4; https://doi.org/10.3390/cosmetics7010004
Received: 5 December 2019 / Revised: 29 December 2019 / Accepted: 30 December 2019 / Published: 1 January 2020
Methylisothiazolinone (MI) is one of the most used preservatives in shampoos and also one of the most effective. A preservative mixture known as Kathon™ CG is commercially available. It contains 5-chloro-2-methyl-4-isothiazolin-3-one (CMI) and 2-methyl-4-isothiazolin-3-one (MI) (3:1) and stabilizers. The aim of this study is to evaluate the influence of formulation factors in the quantification and stability of isothiazolinones in shampoos. Two shampoo bases containing Kathon™ CG as a preservative were prepared. Some ingredients that are at risk of interfering with the preservative stability were added to these formulations. The preservative was quantified by HPLC-DAD (High-performance liquid chromatography with a diode-array detector) after preparation of the formulation and after storage at room temperature and at 40 °C. The addition of magnesium silicate proved to be essential for the breakdown of the interaction between the matrix and the analytes in the extraction procedure. The content of CMI/MI decreased right after preparation indicating that immediate interactions between CMI/MI and the ingredients may have occurred after preparation resulting in a decrease in the preservative concentration. Detrimental interactions between the ingredients, regarding the stability of the isothiazolinones were detected immediately after preparation and over time resulting in the reduction of CMI/MI concentration in these cosmetic shampoos. View Full-Text
Keywords: cosmetics; shampoo; cosmetic ingredients; preservatives; methylisothiazolinone; chloromethylisothiazolinone; dermatitis cosmetics; shampoo; cosmetic ingredients; preservatives; methylisothiazolinone; chloromethylisothiazolinone; dermatitis
MDPI and ACS Style

Tomás, M.; Agonia, A.S.; Borges, L.; Palmeira de Oliveira, A.; Palmeira de Oliveira, R. Isothiazolinones Quantification in Shampoo Matrices: A Matter of Method Optimization or Stability Driven by Interactions? Cosmetics 2020, 7, 4.

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