A method for the simultaneous determination of six preservatives in cosmetic and pharmaceutical prod- ucts, as well as in surface waters, using high performance liquid chromatography (HPLC) has been developed.
Methylisothiazolinone (MI), chloromethylisothiazolinone (CMI), benzyl alcohol (BA), potassium sor- bate (PS), sodium benzoate (SB), and methylparaben (MP) were separated on a Develosil RP Aqueous AR-5 RP-30 (250 x 4.6 mm, 5.0 µm) column, using a gradient elution with acetonitrile and 0.1% aqueous solution of formic acid. Acetonitrile content is increased during the analysis from 15% to 25%. The analysis time was 22 minutes. The linearity ranges of calibration curves for the standards dissolved in methanol are: 1.83-18.33 µg/mL for MI, 2.50-25.00 µg/mL for CMI, 10.00-100.00 µg/mL for BA, 0.50-10.00 µg/mL for PS, and 1.00- 10.00 µg/mL for SB and MP. The linearity ranges of analytes for the water matrix are as follows: 3.17-18.33 µg/mL for MI, 3.50-25.00 µg/mL for CMI, 25.00-100.00 µg/mL for BA, 2.50-15.00 µg/mL for PS, and 2.50- 10.00 µg/mL for SB and MP. The limits of detection and quantification for the determined compounds are within the following ranges: LOD – 0.15-5.3 µg/mL and LOQ – 0.45-16 µg/mL.
The quantitative extraction of analytes from solid samples and liquid samples with a high density and viscosity (cosmetics, pharmaceuticals) of the recoveries order 69-119% was performed using an ultrasound- assisted extraction with methanol. For the purpose of the analysis of environmental water samples, a method for extracting the analytes using solid-phase extraction technique (SPE) also was developed, allowing for the quantitative isolation of the analytes from water samples (recoveries of 65.4-105.6%) and for the 600-fold con- centration. As a sorbent in SPE, cartridges with HLB filling were used (Oasis HLB, 6 mL, 500 mg).
The method developed was applied to the analysis of the following samples: face tonics, creams, lotions, shower gels, face masks, and syrups for the content of determined preservatives, as well as for the detection and identification of its residues in surface waters. Four of the six chosen analytes were identified in the waters. The most detected and determined compound was SB (up to 3.12 µg/L). There are also detected and deter- mined CMI (up to 11.57 µg/L), BA (up to 35.1 µg/L), and MP (in amounts higher than method detection limit but smaller than method quantification limit).
The long-term stability of the compounds in surface waters also was determined. The stability of the determined compounds in environmental water varies, the most stable compounds are MI and BA, while the least stable are CMI and MP.