Determination of polyethoxylated non-ionic surfactants using potentiometric flow injection systems

Solvent extraction and gas chromatography-mass spectrometric determination of probable carcinogen 1,4-dioxane in cosmetic products

In the present work, a method based on solvent extraction and gas chromatography-mass spectrometry (GC-MS) has been validated for the determination of 1,4-dioxane in cosmetics. Various solvents including ethyl acetate, hexane, methanol, dichloromethane and acetone have been used for the extraction of 1,4-dioxane, among them the ethyl acetate was found to be the most efficient extracting solvent. This method has offered excellent quality parameters for instance linearity (R² > 0.9991), limit of detection (LOD, 0.00065-0.00091 µg/mL), limit of quantification (LOQ, 0.00217-0.00304 µg/mL) and, precision intra-day (1.65-2.60%, n = 5) and inter-day (0.16-0.32%, n = 5) in terms of relative standard deviation (RSD%). A total of thirty-nine cosmetic samples of different brands and origin have been studied. Among them, the 1,4-dioxane was found in twenty-three samples (FB₁-FB₇, MC₁-MC₄, MC₆-MC₈, HS₃, HS₅, BL₁-BL₃, BL₅ and PLD₁-PLD₃) at the levels between 0.15 µg/mL and 9.92 µg/mL, whereas in sixteen samples (MC₅, HS₁, HS₂, SG₁-SG₅, BL₄ and HP₁- HP₆) was found to be not detected. The recovery values were achieved between 93% and 99% in both low and high level of spiked samples. In comparison to the traditional analytical techniques, the proposed method was found to be very sensitive and cost-effective for the routine analysis of 1,4-dioxane at low concentration in cosmetics.

Recent advances in flow injection analysis

A dynamic development of methodologies of analytical flow injection measurements during four decades since their invention has reinforced the solid position of flow analysis in the arsenal of techniques and instrumentation of contemporary chemical analysis.

Sensitive Potentiometric Method for Determination of Micromolar Level of Polyethoxylated Nonionic Surfactants in Effluents

The Metrohm NIO surfactant electrode has been used as end-point indicator for potentiometric titration of low concentration level of polyethoxylated nonionic surfactants. This can be achieved by using of a diluted titrant concentration, thus reducing the amount of precipitate formed during titration and preventing the electrode deterioration. The solutions of low levels (down to 10−6 mol/L) of selected nonionic surfactants containing 5 to 23 EO groups were successfully titrated with diluted (as low as 10−4 mol/L) sodium tetraphenylborate as standard anionic titrant, increasing up to 20 times the sensitivity of the method. The low surfactant concentration has been determined in synthetic formulations of widely used detergent products and industrial waste waters. The titration end-point has been determined by applying extended Savitzky-Golay least-squares regression. The accuracy and precision has been evaluated by using the standard addition method. Relative standard deviation within results was between 3.4 and 12.8 % depending on the sample complexity and the surfactant concentration level.

On Plate Resolution and Identification of Three-Component Mixture of Nonionic Surfactants

Silica gel 60 F254 plates were used with mixed aqueous-organic solvent systems consisting of dioxan and lithium chloride for the chromatography of three nonionic surfactants. The resolution of coexisting Triton X-100, Brij-57 and Brij-78 was achieved with the solvent system 1,4-dioxan:1% aqueous LiCl (40:60, v/v). The effect of concentration of Li+ ions in the solvent system on the mobility of the three surfactants was studied. The interference on the resolution of the mixture of Triton X-100, Brij-57 and Brij-78, due to the presence of metal cations as impurities, is also examined. The limits of detection of Triton X-100, Brij-57 and Brij-78 estimated were 0.075, 0.150 and 0.20 μg/zone respectively. The practical applicability of proposed method was tested for the identification of three coexisting nonionic surfactants after their separation from the spiked aqueous systems.

Potentiometric Batch and Flow Injection Analysis of Betaine Hydrochloride

Novel PVC membrane electrodes for the determination of betaine ion based on the formation of betaine-tetraphenylborate (Be-TPB) and betaine-phosphotungstate (Be-PT) ion-exchangers as electroactive materials are described. The sensors show a fast, stable, near Nernstian response for 6.92 x 10(-6) to 7.94 x 10(-3) M and 1.0 x 10(-4) to 1.0 x 10(-2) M betaine hydrochloride (Be.Cl) in case of Be-TPB electrode applying batch and flow injection analysis (FIA), respectively, and 2.95 x 10(-5) to 2.26 x 10(-3) M and 3.16 x 10(-5) to 1.0 x 10(-2) M in case of Be-PT electrode for batch and FIA electrodes, respectively, at 25 degrees C over the pH range of 3.5-10 with a cationic slope of 60.2 and 59.1 mV decade(-1) and a fast potential response of < or =15 s. The lower detection limits are 7.94 x 10(-6) and 3.18 x 10(-5) M Be.Cl for Be-TPB and Be-PT electrodes, respectively. Selectivity coefficient data for some common inorganic cations, sugars, amino acids and the components other than betaine, of the mixed drug investigated show negligible interference. The electrodes have been applied to the direct potentiometric determination of betaine hydrochloride in water and in a pharmaceutical preparation under batch and FIA conditions. Potentiometric titrations of Be.Cl with NaTPB and PTA as titrants were monitored with the developed betaine electrodes as an end point indicator electrode. The determination of Be.Cl shows an average recovery of 100.8% with mean relative standard deviation of 0.61%. The effect of temperature on the electrodes was also studied.

Impurity analysis of 1,4-dioxane in nonionic surfactants and cosmetics using headspace solid-phase microextraction coupled with gas chromatography and gas chromatography–mass spectrometry

1,4-Dioxane impurity in nonionic surfactants and cosmetics were analyzed using solid-phase microextraction (SPME) coupled with gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Experimental results show that there is no significant difference using SPME-GC and SPME-GC-MS for analysis of 1,4-dioxane in three types of nonionic surfactants at the 95% confidence level. The relative standard deviation (R.S.D.) values of each analytical method were smaller than 3%. The amount of 1,4-dioxane was found to vary from 11.6 +/- 0.3 ppm to 73.5 +/- 0.5 ppm in 30% of nonionic surfactants from manufacturers in Taiwan. These methods were linear over the studied range of 3-150 ppm with correlation coefficients higher than 0.995. The recoveries of 1,4-dioxane for these nonionic surfactants following SPME were all higher than 96 +/- 1% (n = 3). The detection limits of 1,4-dioxane for these nonionic surfactants following SPME were from 0.06 ppm to 0.51 ppm. The experimentally determined level of 1,4-dioxane in cosmetics from manufacturers in Taiwan varied from 4.2 +/- 0.1 ppm to 41.1 +/- 0.6 ppm in 22% of daily used cosmetics following SPME coupled with GC and GC-MS. Conventional solvent extraction takes around 1 h for extraction and reconcentration but SPME takes only around 10 min. SPME provides better analyses of 1,4-dioxane in nonionic surfactants and cosmetics than conventional solvent extraction and head space pretreatments in term of simplicity, speed, precision, detection limit, and solvent consumption.