Acid In Cosmetics Research Articles

Chemical Derivatization and Paper Spray Ionization Mass Spectrometry for Fast Screening of Retinoic Acid in Cosmetics.

As a prescription drug, retinoic acid is listed as a banned cosmetic additive in the EU and China regulations. Currently, spectrophotometric methods, including thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and HPLC-MS/MS, are commonly used for the determination of retinoic acid. As these conventional methods require complex pretreatment and are time-consuming, chemical derivatization combined with paper spray ionization mass spectrometry was developed for the fast detection of retinoic acid in cosmetics. N,N-dimethylpiperazine iodide (DMPI) was utilized as a derivatization reagent. Carboxylic acid in retinoic acid was derivatized to carry a positive charge and was subjected to mass spectrometry analysis. Results showed that compared with non-derivatized compounds, the detection limit was increased by about 50 times. The linearity in the range of 0.005-1 μg·mL-1 was good. The limit of detection (LOD) was 0.0013 μg·mL-1, and the limit of quantification (LOQ) was 0.0043 μg·mL-1. The recoveries of spiked samples were in the range of 95-105%, and the RSDs were below 5%. Derivatization and paper spray ionization MS render a quick, sensitive, and accurate method for the detection of retinoic acid in a complex matrix.

A novel Escherichia coli cell–based bioreporter for quantification of salicylic acid in cosmetics

Transcription factor–based bioreporters have been extensively studied for monitoring and detecting environmental toxicants. In Escherichia coli, the multiple antibiotic resistance regulator (MarR) induces transcription upon binding to salicylic acid (SA). We generated SA-specific E. coli cell–based bioreporters utilizing the operator region of the mar operon and MarR as components of the reporter and sensing domains, respectively. Although bioreporters based on endogenous MarR and wild-type E. coli cells responded to SA, their sensitivity and selectivity were insufficient for practical sample monitoring. To improve these parameters, we genetically engineered host strains for optimal MarR expression, which enhanced the sensitivity of the biosensor to micromolar quantities of SA with increased selectivity. Under the optimized experimental conditions, the biosensor could quantify SA in environmental samples. For validation, the SA concentration in artificially contaminated SA-containing cosmetic samples was determined using the developed biosensor. Reliability assessment by comparing the concentrations determined using LC–MS/MS revealed > 90% accuracy of the bioreporters. Although bioreporters are not considered standard tools for environmental monitoring, bacterial cell–based bioreporters may serve as alternative tools owing to their affordability and simplicity. The SA biosensor developed in this study can potentially be a valuable tool for monitoring SA in environmental systems.Key points• SA-responsive bioreporter is generated by employing mar operon system in E. coli• SA specificity and selectivity were enhanced by genetic/biochemical engineering• The novel bioreporter would be valuable for SA monitoring in environmental systems

Safety Assessment of Ginkgo biloba-Derived Ingredients as Used in Cosmetics.

The Expert Panel for Cosmetic Ingredient Safety (Panel) assessed the safety of 10 Ginkgo biloba-derived ingredients, which are most frequently reported to function in cosmetics as skin conditioning agents or antioxidants. The Panel reviewed the available data to determine the safety of these ingredients. Because final product formulations may contain multiple botanicals, each containing the same constituents of concern, formulators are advised to be aware of these constituents and to avoid reaching levels that may be hazardous to consumers. The Panel was concerned about the presence of ginkgolic acid in cosmetics. Industry should use good manufacturing practices to limit impurities. The Panel concluded that 5 Ginkgo biloba leaf-derived ingredients are safe in the present practices of use and concentration described in this safety assessment when formulated to be non-sensitizing; data are insufficient to determine the safety of the remaining 5 ingredients under the intended conditions of use in cosmetic formulations.

Kinetic spectrophotometric assay for the determination of vitamin C in cosmetics following ultrasound-assisted emulsification.

In this work, a new analytical approach based on ultrasound-assisted emulsification followed by a photoreaction with methylene blue (MB) and kinetic analysis by UV-vis spectrophotometry has been developed for the determination of L-ascorbic acid (AA) in cosmetic samples. The emulsification of cosmetic samples results in a transparent solution that allows an easy and rapid quantitation by UV-vis spectrophotometry. The emulsified sample is mixed with a MB aqueous solution and this mixture is subjected to irradiation with a tungsten lamp for 5 min (fixed-time kinetic assay). A reduction in the MB absorbance intensity at 664 nm occurs as the concentration of AA increases. The observed change in absorbance intensity was used for calibration and further quantitation using the relationship of absorbance logarithm vs. AA concentration (μg mL-1). In order to achieve an optimal response, different parameters involved in the reaction between AA and MB were fully investigated. Under optimal conditions, the limits of detection and quantification were 0.04 μg mL-1 and 0.15 μg mL-1, respectively. Repeatability and reproducibility, expressed as relative standard deviation, were in the range of 0.4-0.6% and 0.6-1.5%, respectively. Finally, the proposed method was applied to the analysis of 15 cosmetic samples, namely, (i) 12 samples without AA, which were used to carry out recovery studies, obtaining results in the range of 97.5-100.7%; (ii) 3 serum samples containing pure AA among their ingredients, which were used for AA stability studies.

Simple Portable Voltammetric Sensor Using Anodized Screen-Printed Graphene Electrode for the Quantitative Analysis of p-Hydroxybenzoic Acid in Cosmetics.

Screen-printed graphene electrodes (SPGEs) have become a potential option in electrochemical applications because of their outstanding properties and disposable approach to miniaturize the electrodes for onsite analysis. Herein, the detection of para-hydroxybenzoic acid (PHBA) in cosmetics using the anodized SPGE has been pioneered and reported. The simple anodization of the SPGE surface was operated by anodic pretreatment at a constant potential on SPGE. The surface morphologies and electrochemical behaviors of anodized SPGEs in different anodization electrolytes were examined. Using anodized SPGE in a phosphate-buffered solution, a nontoxic solution, the sensitivity of PHBA detection was significantly improved compared with pristine SPGE owing to the increase of the polar oxygen-containing functional group during the anodization. The anodized SPGE could detect a PHBA down to 0.073 μmol/L. Finally, the developed anodized SPGE presented high ability and feasibility for PHBA detection in cosmetics. Furthermore, a facile electrode preparation step with a nontoxic solution can present high reproducibility and compatibility with a portable potentiostat for onsite PHBA detection during manufacturing.

Optimization of Experimental Procedure for Determining Azelaic Acid in Cosmetics by Gas Chromatography Derivatized through Ethanol.

The quantitative evaluation of azelaic acid is becoming critical in the development of new medicinal products and in environment. A feasible method for the determination of azelaic acid in cosmetics by gas chromatographic-mass spectrometer detector (GC-MS) with derivation was developed and optimized. The derivative effect was good, when azelaic acid was derivatized through ethanol at room temperature for 10 min with 800 μL of sulfuric acid as a catalyst. A good linear relationship of azelaic acid derivative was present from 10 to 1000 mg L–1 (R2 = 0.9997). Detection limit and quantitative limit of GC was 15 and 50 mg kg–1, respectively. The recovery rate was in the range from 87.7% to 101% with all relative standard deviation (RSD) values less than 4%, denoting the method meeting the requirement of the analysis. Therefore, this method has the advantages of strong anti-interference ability and accurate results. Among the eight samples nominally azelaic acid, only three were detected. The respective content was 78 133, 16 710, and 2431 mg kg–1. The results showed that the actual addition of the azelaic acid in the market was quite different with label identification, being worthy of further attention. Further, it also provided a favorable experience for the monitoring of azelaic acid in the environment.

Surface-Bonding-Enhanced Self-Co-Reactant Electrogenerated Chemiluminescence for Sensitive and Selective Detection of Thioglycolic Acid in Cosmetics.

Thioglycolic acid (TGA) is an organic compound widely used in cosmetics that cause a variety of health problems when overexposed to it. So far many attempts have been made to develop methods for TGA detection, but most of them need sophisticated instrumentations and are a little bit complicated. Therefore, a simple, cheap and sensitive detection method of TGA is highly desired. Herein, we demonstrated for the first time an Au-S bonding amplified, highly sensitive electrochemiluminescence (ECL) sensing method for TGA detection using tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3 2+ ) as a luminophore and TGA as a self-co-reactant, via an anodic reaction at the Au electrode surface. Due to different molecular coordination environments of the TGA at the electrode surface, the ECL signal intensity of the developed ECL system gives much higher ECL signal in borate buffer than phosphate buffer of the same pH. Under the optimized experimental conditions, the ECL intensity has a direct relationship with the concentration of TGA in the range of 0.03 μM to 300 μM and a limit of detection of 0.013 μM (3σ/m). The reported ECL system has further been applied for the detection of TGA in cosmetics with acceptable recoveries.

Development of a Novel Electrochemical Biosensor Based on Carbon Nanofibers-Gold Nanoparticles-Tyrosinase for the Detection of Ferulic Acid in Cosmetics.

The present paper deals with the electrochemical behavior of three types of sensors based on modified screen-printed electrodes (SPEs): a sensor based on carbon nanofibers (CNF/SPE), a sensor based on nanofibers of carbon modified with gold nanoparticles (CNF-GNP/SPE) and a biosensor based on nanofibers of carbon modified with gold nanoparticles and tyrosinase (CNF-GNP-Ty/SPE). To prepare the biosensor, the tyrosinase (Ty) was immobilized on the surface of the electrode already modified with carbon nanofibers and gold nanoparticles, by the drop-and-dry technique. The electrochemical properties of the three electrodes were studied by cyclic voltammetry in electroactive solutions, and the position and shape of the active redox peaks are according to the nature of the materials modifying the electrodes. In the case of ferulic acid, a series of characteristic peaks were observed, the processes being more intense for the biosensor, with the higher sensitivity and selectivity being due to the immobilization of tyrosinase, a specific enzyme for phenolic compounds. The calibration curve was subsequently created using CNF-GNP-Ty/SPE in ferulic acid solutions of various concentrations in the range 0.1–129.6 μM. This new biosensor allowed low values of the detection threshold and quantification limit, 2.89 × 10−9 mol·L−1 and 9.64 × 10−9 mol·L−1, respectively, which shows that the electroanalytical method is feasible for quantifying ferulic acid in real samples. The ferulic acid was quantitatively determined in three cosmetic products by means of the CNF-GNP-Ty/SPE biosensor. The results obtained were validated by means of the spectrometric method in the infrared range, the differences between the values of the ferulic acid concentrations obtained by the two methods being under 5%.

Flow injection analysis of kojic acid in cosmetics by a carbon-nanotube modified screen-printed electrode

A novel carbon-nanotube modified screen-printed electrode (CNT/SPE) was successfully prepared and validated to be a useful detector in the flow injection system. Compared to a bare screen-printed electrode (SPE), CNT/ SPE improved the detection limit for kojic acid (KA). The detection limit on S/N = 3 was as low as 0.01 ppm. Furthermore, several factors, including the pH, applied potential, flow rate and coating quantity of CNT, were assessed. The attractive response of CNT/SPE has allowed it to be used for constant-potential FIA (Flow-Injection Analysis) of KA and indicates great potential for monitoring chromatographic effluents. The linear relationship between KA concentration (0.1-120 ppm) and the current response was established. Meanwhile five different CNT/SPEs for the detection KA of 20 ppm yielded a RSD value of 4.43%, indicating acceptable reproducibility of the present analysis. Finally, two real samples on the market were analyzed using the proposed system with appreciable results.

Development and validation of a reversed-phase high-performance liquid chromatographic method for the quantitation and stability of α-lipoic acid in cosmetic creams.

To develop and validate a simple reversed-phase HPLC method for the quantitation and evaluation of stability of α-lipoic acid in cosmetics, according to International Conference on Harmonization (ICH) Guidelines. The chromatography was performed on a reversed-phase Luna C18, analytical column (150×4.6mm id, 5μm particle size) with a mobile phase of potassium dihydrogen phosphate (pΗ 4.5; 0.05M) and acetonitrile (60:40, v/v) and a flow rate of 1.0mLmin-1 with UV detection at 340nm. Accelerated and long-term stability studies of α-lipoic acid in cosmetic cream were conducted under various degradation conditions including acid, basis, oxidation, and thermal and photolytic degradation, according to European Medicines Agency Guidelines CPMP/ICH/2736/99. The limit of detection (LOD) for the cosmetic cream was 0.9μgmL-1 and the limit of quantitation (LOQ) was 2.8μgmL-1 , while the retention time was 7.2min. The method proved to be linear, precise and accurate. The stability results demonstrated the selectivity of the proposed method to the analysis of α-LA, and the degradation products were determined and evaluated in specific stress conditions in cosmetic creams. The applicability of the method was tested in two different developed cosmetic products (cream with 1.5 % w/w and emulsion with 1.0 % w/w of LA) and proved to be reliable. A reversed-phase HPLC-UV method was developed and fully validated for the analysis of α-lipoic acid in cosmetics. It is the first reported application on the quantitation of lipoic acid in cosmetic creams, while at the same time evaluates the stability in forced degradation conditions, in new cosmetic formulations. It proved to be suitable for the reliable quality control of cosmetic products, with a run time of <8min that allows for the analysis of large number of samples per day.

A simple capture-release strategy based on an instantly formed mixed metal hydroxide sorbent for determination of salicylic acid in cosmetics

We present a simple eco-friendly extraction-release strategy for enhancing the assessment of salicylic acid (SA) in cosmetic samples. Given that the extraction and the formation of mixed metal hydroxides (MMHs) acting as sorbent occurred at the same time, the in situ solid phase extraction (is-SPE) of SA was achieved by mixing magnesium and aluminium ions in an alkaline sample solution. After the is-SPE, the MMHs precipitates were isolated by centrifugation and dissolved completely in sulfuric acid. Subsequently, the released SA was quantified by spectrophotometry at 237 nm. The is-SPE parameters including the amount of hydroxide ions, amount of metal ions, extraction time, and centrifugation time were studied thoroughly. Under the optimized conditions, this method provided the linear range of 0.15–2 mg L−1 with the relative standard deviations of less than 7.20% and the limit of detection of 45 μg L−1. In addition, the proposed method was successfully applied for SA analysis in toner, foam, and serum samples with reasonable relative recoveries in the range of 76.3–100.3%. This method eliminated the use of organic solvents and avoided the synthesis step of sorbents as well as their characterization, thus saving time, chemicals, and energy.

Polyethylenimine-capped silver nanoclusters as fluorescent sensors for the rapid detection of ellagic acid in cosmetics

Polyethylenimine-capped silver nanoclusters (PEI-AgNCs) are being developed as fluorescent sensors because of their high fluorescence, excellent photostability and large Stokes shift. In this study, PEI-AgNCs demonstrate characteristic absorption peaks at 268 and 360 nm with the strongest blue fluorescence emission at 436 nm. The PEI-AgNCs are spherical, and their average diameter is 3.7 ± 1.8 nm. In addition, the quantum yield of the PEI-AgNCs is 3.03%. A sensitive, selective and rapid detection technique for ellagic acid has been developed utilizing a fluorescent PEI-AgNC sensor. Ellagic acid exhibits tyrosinase inhibition and antioxidative properties and is hence always added in cosmetics as a skin whitening ingredient. The reaction can be completed within 60 s in Britton-Robinson buffer at pH 11. The fluorescence quenching mechanism is assumed to be static quenching because the fluorescence lifetime of PEI-AgNCs without and with ellagic acid did not obviously change. Moreover, the quenching intensity of the PEI-AgNCs is linearly related to the ellagic acid concentration over the range from 0.1 μg/mL to 30.0 μg/mL with good linear correlation (r = 0.999), and the detection limit is 33.5 ng/mL. Finally, PEI-AgNCs have also been applied in the detection of a cosmetics containing ellagic acid.

New Perspectives on the Efficacy of Gallic Acid in Cosmetics & Nanocosmeceuticals.

Gallic acid (GA-3,4,5-trihydroxybenzoic acid), a phenolic phytochemical, is a ubiquitous secondary metabolite found in most plants, with appreciable concentrations in grapes seed, rose flowers, sumac, oak and witch hazel. GA often results from the hydrolysis of terpenes and the polyphenol tannic acid. It exhibits powerful antioxidant, anti-inflammatory, antimicrobial, and anti-cancer activities. Most intriguing benefit has been reported to be on the skin. Due to these beneficial properties, GA and its derivatives (e.g. lipid-soluble phenols such as synthetic gallic esters aka gallates) have been extensively used as an adjuvant in a number of therapeutic formulations, as a substitute of hydrocortisone in children with atopic dermatitis (AD) and other skin conditions (hyperpigmentation, wound healing), and as a cosmetic ingredient. GA has a USFDA GRAS status (generally recognized as safe), exhibiting fairly low systemic toxicity and associated mortality at acute doses in many experimental models. Despite anti-skin aging benefits obtained with relatively safe GA formulations, few cases of gallate-induced skin allergic have been reported in humans. Therefore, approaches to improve the bioavailability and biodegradability of this poor-water soluble and non-biodegradable phenolic compound are warranted. This review has focused on the recently reported biological activities pertaining to the skin as well as the pharmacological properties of GA and its derivatives with special emphasis on its use in (nano-) cosmetic formulations. Since this is an evolving area of research, an adequate emphasis has been placed upon advantages and disadvantages of various nanoformulations.

Experimental and statistical analysis on a nanostructured sensor for determination of p-hydroxybenzoic acid in cosmetics

In this research, differential pulse voltammetry (DPV) coupled with experimental design, was used for determination of p-hydroxybenzoic acid (PHB) in cosmetics. Optimization of effecting parameters was carried out based on rotatable central composite design (RCCD) and response surface methodology (RSM) at the surface of a nanostructured electrode for achieving the best sensitivity. Sol-gel process was used for synthesize of nickel titanate (NiTiO3) nanoceramics. The structural and morphological characterization of the nanoparticles was studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Then the NiTiO3 nanopowders were used for surface modification of a carbon paste modified electrode (CPE). Surface characterization of the electrode was accomplished using SEM, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Under the optimized conditions, the voltammograms exhibited two linear dynamic ranges of 0.7–80.0 μM and 80.0–1000.0 μM for PHB with the detection limit of 62.0 nM (S/N = 3). Finally the NiTiO3 nanoceramics modified carbon paste electrode (NiTiO3/CPE) could be employed for the determination of PHB in real samples with satisfactory results.

Development of ultrasonic-assisted closed in-syringe extraction and derivatization for the determination of labile abietic acid and dehydroabietic acid in cosmetics

Two resin acids, abietic acid (AA) and dehydroabietic acid (DHAA), in cosmetics may cause allergy or toxicoderma, but remain inaccurately investigated due to their lability. In this work, an accurate, sensitive, efficient and convenient method, utilizing the ultrasonic-assisted closed in-syringe extraction and derivatization (UCSED) prior to high performance liquid chromatography (HPLC) coupled with fluorescence detection (FLD) and on-line tandem mass spectra (MS/MS), has been developed. Analytes are extracted by acetonitrile (10/1, v/m) in a sealed syringe under safe condition (60°C; 15min; nitrogen atmosphere) and then in-syringe derivatized by 2-(2-(anthracen-10-yl)-1H-naphtho[2,3-d]imidazol-1-yl) ethyl-p-toluenesulfonate (ANITS) (8-fold, 93°C, 30min, DMF as co-solvent, K2CO3 as catalyst). In UCSED, derivatization contributes to increase both analytical sensitivity and stability of analytes. Excellent linearity (r2≥0.9991) is achieved in wide range (75–3000ng/mL (AA); 150–4500ng/mL (DHAA)). Quite low detection limits (AA: 8.2–10.8ng/mL; DHAA: 19.4–24.3ng/mL) and limits of analyte concentration (LOAC) (AA: 30.0–44.5ng/mL; DHAA: 70.9–86.7ng/mL) ensure the trace analysis. This method is applied to the analysis of cosmetic samples, including depilatory wax strip, liquid foundation, mascara, eyeliner, eyebrow pencil and lip balm. No additional purification is required and no matrix effect is observed, demonstrating obvious advantages over conventional pretreatment such as solid phase extraction (SPE). Accuracy (RE: −3.2% to 2.51%), precision (RSD: 1.29–2.84%), recovery (95.20–103.63%; 95.51–104.22%) and repeatability (<0.23%; <2.87%) are significantly improved. Furthermore, this work plays a guiding role in developing a reasonable method for labile analytes.

Chemical derivatization combined with capillary LC or MALDI-TOF MS for trace determination of lipoic acid in cosmetics and integrated protein expression profiling in human keratinocytes

Lipoic acid (LA) is an essential cofactor in mitochondrial enzymes and an ideal antioxidant in prokaryotic and eukaryotic cells. Capillary liquid chromatography coupled with ultraviolet detection (CapLC–UV) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) are two environmentally friendly methods for determining LA. In this study, a pre-column microwave-assisted derivatization with 4-bromomethyl-6,7-dimethoxycoumarin enhanced the UV absorbance of LA and was monitored at 345nm by CapLC–UV. Gradient separation was performed using a reversed-phase C18 column with a mobile phase consisting of acetonitrile–0.1% formic acid solution. The ionization of LA was increased, and the LA derivative was detected by MALDI-TOF MS at m/z 683 with an α-cyano-4-hydroxycinnamic acid matrix. The linear response ranged from 0.1 to 40μM with a correlation coefficient of 0.999. The CapLC–UV and MALDI-TOF MS had detection limits of 5 and 4fmol, respectively. These methods effectively detected LA in dietary supplements and cosmetics. Cellular proteomes of a human keratinocyte cell line (HaCaT) irradiated with UV radiation were also compared with and without LA treatment. The cellular proteomes were identified by nanoultra performance LC with LTQ Orbitrap system after trypsin digestion. Protein identification was performed by simultaneous peptide sequencing and MASCOT search. The analysis revealed changes in several proteins, including CDC42, TPI1, HNRPA2B1, PRDX1, PTGES3 and MYL6.

Synthesis of Carboxymethyl Polysaccharides and Their Moisture Absorption and Retention Abilities

In this study, carboxymethyl hyaluronic acid, carboxymethyl starch and carboxymethyl chitosan were successfully prepared. The characterization of carboxymethyl hyaluronic acid was identified by IR and NMR techniques. The moisture absorption and retention abilities of these products were examined. Results showed that carboxymethyl hyaluronic acid, as well as carboxymethyl starch and carboxymethyl chitosan, had better moisture absorption and retention abilities both at 43 and 81 % relative humidity than the corresponding polysaccharide and hyaluronic acid. It is concluded that carboxymethylation could improve greatly the moisture absorption and retention abilities of polysaccharides and that carboxymethyl hyaluronic acid, carboxymethyl starch and carboxymethyl chitosan all would be very promising to be used as moisture absorption and retention ingredients instead of hyaluronic acid in cosmetics and in certain other fields.

Determination of thioglycolic acid in cosmetics by capillary electrophoresis

A new and simple method for the accurate determination of thioglycolic acid (TGA) in cosmetics was developed using capillary electrophoresis (CE) with diode array detection at 236nm. The CE separation was performed on an uncoated fused silica capillary with a separation buffer solution containing 300mmolL−1 tri-sodium phosphate and 0.5mmolL−1 cetyltrimethylammonium bromide at a voltage of −5kV. Both the intra- and inter-day precisions of the method were 1.4%. The calibration curve between the corrected peak areas and the concentrations of the TGA was linear within the concentration range of 0.006–1.0mgmL−1 with a correlation coefficient (r) of 0.9998. The limit of detection and limit of quantitation were 0.002mgmL−1 (S/N=3) and 0.006mgmL−1 (S/N=10), respectively. The average recoveries at the spiked levels of 0.125, 0.250 and 0.500mgmL−1 were 96.9%, 102.3% and 94.0% with the relative standard derivations of 2.1%, 3.9% and 2.2%, respectively. The method was cross-validated by both high performance liquid chromatographic and ion chromatographic method. Eighty-five commercial depilatory creams and hair-treatment products were analyzed with satisfactory results.

Determination of phenolic whitening agents in cosmetics by micellar electrokinetic capillary chromatography with amperometric detection

Abstract A sensitive method for simultaneous determination of six phenolic whitening agents, including arbutin, phenol, resorcinol, hydroquinone, kojic acid, and salicylic acid in cosmetics has been developed using micellar electrokinetic capillary chromatography with amperometric detection (MECC-AD). Effects of several factors, such as the pH value and concentration of running buffer, potential applied to the working electrode, separation voltage, and injection time were investigated to obtain optimum conditions for separation and detection. With a 75 cm long fused-silica capillary tube, well-defined separation of six phenolic compounds was achieved in 10 mmol/L SDS/40 mmol/L H3BO3–Na2B4O7 running buffer (pH 9.0). Good linear relationship was obtained for each analyte over three orders of magnitude with correlation coefficients (r2) between 0.9985 and 0.9994, and the detection limit (S/N = 3) ranged from 0.04 μg/mL to 0.45 μg/mL. The proposed method has been successfully applied for the determination of phenolic whitening agents in real cosmetic samples with satisfactory results, providing an alternative monitoring method for cosmetics safety regulation.

Photometric determination of thioglycolic acid in cosmetics by using a stopped-flow reverse flow-injection system and the formation of gold nanoparticles

The positive effect of thiol compounds as reducing agents in the synthesis of gold nanoparticles in the presence of a micellar medium of Triton X-100 has been photometrically studied using a reverse flow-injection system which operates in the stopped-flow mode (SF-rFIA). The analytical usefulness of this new system has been assessed by its application to the determination of thioglycolic acid (TGA), which was chosen as the analyte model. The dynamic range of the calibration graph was 5.97–80 μmol L −1, and the detection limit was 1.73 μmol L −1. The behaviour of other thiol compounds on the system has been also studied. The precision of the method, expressed as relative standard deviation, ranged between 1.5 and 2.3%. The method was applied to the determination of TGA in several cosmetic samples with acceptable recoveries in all instances, which ranged between 90.32 and 101.46%.