*2.3.4 Analytical curve for the identification of formaldehyde*

The identification of formaldehyde in the solutions was done through the reaction that occurs between the chromotropic acid and formaldehyde in the presence of magnesium after heating, thus producing a colored compound, indicating the presence of formaldehyde in a solution. For the determination of the analytical curve of formaldehyde, the following test was performed: 90, 120, 150, 180, 210, 220, and 230 μl of stock solution containing formaldehyde were transferred to test tubes. In Then, 290 μl of solution of 5% (w/v) chromotropic acid and 3.0 ml of solution of 60% (w/v) magnesium sulfate, with stirring. The tubes were heated for 60 minutes in a steam (100°C), followed by cooling to 25°C. The solutions were transferred to 25 ml flasks and the volume filled with distilled water, obtaining the concentrations of formaldehyde (ppm): 3.6, 4.8, 6.0, 7.2, 8.4, 8.8, and 9.2, respectively. The measurements of absorbance were recorded at 535 nm. All reviews were carried out in triplicate, in order to guarantee the accuracy of the results obtained.

*Cosmetovigilance in Hair Straighteners: Determination of Formaldehyde Content… DOI: http://dx.doi.org/10.5772/intechopen.82842*

#### *2.3.5 Determination of formaldehyde in the sample*

For each commercial sample, 3.0 g was weighed and then dissolved in about 20 ml of distilled water, and the final volume was completed to 100 ml, yielding a solution with concentration (C1) of 30,000 μg ml<sup>−</sup><sup>1</sup> . After 5.0 ml of this solution (C1) were diluted in 25 ml of distilled water (C2 = 6000 μg ml<sup>−</sup><sup>1</sup> ). Aliquots of 1.0 ml of the solutions (C2) were transferred to test tubes together with 290 μl of chromotropic acid 5% (w/v) and 3.00 ml of magnesium sulfate 60% (w/v). The tubes were heated for 60 minutes in a steam bath (100°C), followed by cooling to 25°C. The solutions were transferred to 25 ml volumetric flasks, and then the volume was filled with distilled water resulting in a concentration (C3) of 240 μg ml<sup>−</sup><sup>1</sup> . The measurements of absorbance were performed at 535 nm.

#### *2.3.6 Organoleptic and physicochemical properties*

The organoleptic and physicochemical tests were performed to assess the characteristics of the products in study. The organoleptic and physicochemical characteristics evaluated were odor, color, appearance, pH, viscosity, density, and centrifugation [13], which were correlated between samples.

#### *2.3.7 Determination of pH*

For the determination of the pH, the potentiometric method was used. The samples were diluted to 10% (w/v) in distilled water, at room temperature, in triplicate [13–15].

#### *2.3.8 Determination of viscosity*

The viscosity was measured in triplicate in an analog rotary viscometer using 40 g of sample, spindle 4 and speed of 6 rpm. Next, the rotor was inserted vertically into the sample free of blister up to the groove of the rotor rod, and the apparatus was leveled, by reading the viscosity according to the operating procedure of the device [13].

#### *2.3.9 Determination of density*

The density was determined by pycnometry. Initially the empty pycnometer (M0) was weighed, first, with distilled water (M1) and, finally, (clean and dry) with the sample (M2). The masses were noted for calculation using the following formula [13]:

$$\mathbf{q} = \frac{\mathbf{M}\_{\hat{x}} - \mathbf{M}\_{\hat{\mathbf{q}}}}{\mathbf{M}\_{\hat{x}} - \mathbf{M}\_{\hat{\mathbf{q}}}}$$

where d is the sample density in g/cm3 ; M0 is the mass of the empty pycnometer, in grams; M1 is the mass of the pycnometer with distilled water, in grams; and M2 is the mass of the pycnometer with the sample, in grams.

#### *2.3.10 Centrifuge test*

From each sample, 5 g was placed in centrifugal tubes and submitted to cycles of 1000 and 2500 rpm for 15 minutes each. The homogeneity of the study formulations was evaluated by observing macroscopic separation of phases after performing the described procedure [13, 14, 16].

*Beauty - Cosmetic Science, Cultural Issues and Creative Developments*

#### **Figure 1.**

*Mandatory items on labeling of capillaries straighteners according to Annexes IV and V of DRC 211/2005.*

#### *2.3.11 Label analysis*

A qualitative analysis of the primary and secondary packaging of the tested products by a critical visual investigation was carried out, following the criteria laid down by national legislation—RDC 211/2005 which defines the labeling rules for cosmetic products [17] and RDC 332/2005 which deals with regulation and implementation of cosmetology in the cosmetic industries [6]. The analyzed items were specified according to **Figure 1**.

#### **3. Results**

#### **3.1 Analytical curve for the identification and determination of formaldehyde**

The identification of formaldehyde was evidenced by the production of a pink compound resulting from the reaction between chromotropic acid and formaldehyde in the presence of magnesium sulfate. The analytical curve data, resulting from the average of three calibration curves, were adjusted by linear regression (**Figure 2**), whose equation of the line is given by absorbance = 0.0922 × [formaldehyde solution, chromotropic acid, and magnesium sulfate] (ppm) − 0.0234. The correlation coefficient obtained was 0.996, a significant linear regression. Samples A1, A3, A5, and A8 developed a coloration after heating, indicating the presence

*Cosmetovigilance in Hair Straighteners: Determination of Formaldehyde Content… DOI: http://dx.doi.org/10.5772/intechopen.82842*

**Figure 2.**

*Graphical representation of the formaldehyde analytical curve using chromotropic acid (AC) and sulfate of magnesium (MgSO4) at 535 nm where Y = 0.0922, x = 0.0234, and R = 0.996.*


#### **Table 3.**

*Absorbances, concentrations of formaldehyde in diluted samples (ppm) and percentages of formaldehyde in the formulations A1–A8.*

of formaldehyde in these formulations, which tends to be as darker as greater the concentration of said substance. The samples A3 and A8, on the other hand, presented more intense in relation to others, which justifies a higher concentration of formaldehyde. The percentages of formaldehyde calculated by the equation from the analytical curve confirm these results and are described in **Table 3**.

#### **3.2 Organoleptic and physicochemical characteristics**

The results obtained in organoleptic and physicochemical tests of the study samples are listed in **Table 4**. Regarding appearance and color, observed macroscopically, the samples presented as homogeneous creams, whether or not colored and without precipitation or exudation. The odor was checked directly through the smell, being possible to smell characteristic of formaldehyde in samples A1, A3, A5, and A8, capable of causing some mucosal irritation and burning in the eyes during observation, confirming symptoms caused by exposure to formaldehyde. The sample A5, although with a strong chocolate odor, failed to mask the presence of formaldehyde in the product. Samples A6 and A7 showed an odor of sulfur, a characteristic of thioglycolic acid. The samples A2 and A4 presented no strong or unpleasant smell, only the essence odor used in these products.

Samples A2 and A4 showed a pH of very acid (1.0 and 1.3, respectively), which may damage the capillary wires [18]. In the other hand, the sample A8 has a pH

#### *Beauty - Cosmetic Science, Cultural Issues and Creative Developments*


#### **Table 4.**

*Organoleptic and physico-chemical characteristics of the formulations under study.*

**Figure 3.**

*Average values of the viscosity (cP) of the samples A1–A8 at 25°C.*

within the range that tends to assist in the maintenance of wires. The samples A1, A3, and A5 also have a pH slightly acidic, being able to close the capillary cuticle and help in preserving the color deposited in the hair. The samples A6 and A7 presented extremely high pH, a characteristic of products for permanent straightening.

The analyzed samples did not present significant variation in relation to the determination of the density and did not need to correct the weighing to carry out the dosing of the formaldehyde.

The formulations showed without phase separation, precipitation, formation of caking, and coalescence, except the A2 sample that presented phase separation after being subjected to the centrifugation.

The viscosity results can be in **Figure 3**. These results point to discrepant values between formulations, ranging from extremely low (A2) to extremely high (A6 and A7).

#### **3.3 Label analysis**

The results of the analysis of the product labels are presented in **Table 5**. Samples A1, A3, A5, and A8 presented formaldehyde content in the procedure *Cosmetovigilance in Hair Straighteners: Determination of Formaldehyde Content… DOI: http://dx.doi.org/10.5772/intechopen.82842*


**Table 5.**

*Analysis of the labels of the products under study according to Annexes IV and V to DRC 211/2005.*

spectrophotometric assay; however, only samples A1 and A8 indicated formaldehyde in their composition. Samples A3 and A5, in addition to the absence of the substance, presented other irregularities on the label, both ignoring the warning information and usage restrictions. Sample A5 does not yet have registration number granted by ANVISA, evidencing the likely clandestine origin of this product.

The samples A2, A4, A6, and A7, whose labels said formaldehyde-free, are not really content of the substance, being in compliance and complying with the technical requirement legislations.
