Absorption of Salicylic Acid in Skin
After Repeated Usage of Facial
Cleansers
ASHLEY COVELLI
CHEM 4101
D E C E M B E R 8 TH, 2 0 1 0
What is Salicylic Acid?
 Compound found naturally in willow tree, “Salix
alba,” then prepared using Kolbe-Schmidt process
 Purpose in cosmetic products: anti-acne agent, skin-
conditioning agent, reported to enhance percutaneous penetration of
other chemical agents in solution1
 Problem: Salicylic acid is believed to be harmful to humans/animals
(if found above toxic threshold of 30 mg/100mL), causing problems
such as: skin irritation, increased sun sensitivity, and reproductive and
developmental toxicity at concentrations ≤3% in personal care
products1
Hypothesis
 Hypothesis:
Salicylic acid is hazardous to
human health upon repeated
exposure. Most facial cleansers
contain roughly 2% of salicylic
acid. The concentration levels
of this compound found below
the skin in humans will be
analyzed, the analyte
concentration in serum should
be below the toxic threshold of
30 mg/100mL using a proper
analytical method.
 Importance of solving
the analytical problem:
By analyzing the amount of
salicylic acid in products and
comparing these
concentrations to
concentrations of salicylic acid
present below the dermis,
would help the FDA regulate
hazardous cosmetic products.
As a result of this study,
cosmetic companies may wish
to reformulate their products in
order to provide a less
hazardous product for
consumers.
Summary of Other Analytical Techniques…
Method
Advantages
Disadvantages
CZE with UV-Vis
Detector2
CZE enables a detection of a large
variety of analytes to be analyzed,
2 μg/mL to be detected in
solution using a simple buffer
(with a pH around 8.8)
The analyte must first be
derivatized before analyzed using
this method, as analytes separate
based on charge once voltage is
applied.
UV-Vis Absorbtion1
Absorbances of various solutions
may be analyzed to determine
concentration of analyte in
cleanser (pure salicylic acid
should absorb in 305-310 nm
range), minimal preparation
needed
Interfering substances may be
present in solution (i.e. water),
small uncertainties may arise
when obtaining absorbances due
to the difficulty of reproducing
the exact wavelength setting
ESI-MS3
High sensitivity, low LOD, low
signal-to-noise ratio (0.1μL-1)
Qualitative analysis, but not an
efficient way to quantify salicylic
acid in solution, expensive
IR
Good for qualitative analysis, fast
method, multiple scans, distinct
functional groups found in
analyte may be seen in
fingerprint region
Presence of water and other
analytes may be problematic, it
may be hard to distinguish
frequencies because of
overlapping vibrational modes
Analytical Method of Choice: HPLC with UV-Vis detector
 Sensitive method which
 System is reasonably
is needed when analyzing
low concentrations
 Small sample volumes
needed
 Quantitative
determination of analyte
concentration in solution
 Relatively low limit of
detection (around 0.1
μg/mL for analyte)1
priced ($1,425 for C8
column and UV detector)
 After analyzing, sample
is not destroyed.
 Relatively good
reproducibility
HPLC column (Ascentis® C8 column – 581444-U Supelco)4 and UV
detector (Agilent 325 Dual Wavelength UV-Vis HPLC Detector)5
Reverse phase HPLC column (size=25 cm × 10.0 mm)4: (approximately $425.00)
 Main advantage is the control of elution selectivity
 Particle size of salicylic acid is <7.4 μm6
 Mobile phase: combinations of methanol and water
 Stationary phase: C8 packing (octyl) on silica gel with added buffer (i.e. sodium
phosphate)
 Flow rate: approximately 1 mL/min6
UV Detector 5 (approximately $10,000):
 Excellent quantitative technique
 Internal Standard to obtain calibration curve
 Absorbances obtained at wavelength range: 305-310 nm due to salicylic acid6
 From Beer’s law plot, concentration of salicylic acid can be determined
 Rapid analysis
 Relatively high sensitivity (around 0.1 μg/mL for analyte)1
Experimental
Design
Prepare Internal Standard and
standard solutions
1.SubcutaneousMicrodialysisobt
ain blood samples
2. Centrifuge the blood samples to
obtain plasma
3. Inject samples into HPLC-UV
vis instrument
4. Obtain an absorbance spectrum
of solution, the wavelength
absorbed in the range 305310 nm is due to salicylic
acid.
1.
Flow rate: 1 mL/min
Mobile Phase: methanol/water
Stationary Phase: C8
Figures of Merit for Analytical Method of Choice1:
ANALYTIC CHARACTERISTICS USING
SIMILAR METHODS:
Parameter
Salicylic Acid
Retention Time
5.5 minutes
Limit of Detection
0.1 μg/mL
Concentration Range
0.04-3.0 mol salicylic acid/mL
Limit of Quantification
0.3 μg/mL
Reproducibility
3%
UV-vis Absorption
305-310 nm
Signal to noise ratio
>3
Linearity Curve
R2=0.9982
Proposed Analysis
 Retention time for Salicylic
 Compare the levels of SA in
acid=5.5 minutes
 Quantify concentration of
Salicylic acid in serum
based on absorbance values
obtained from UV detector
and calibration plot
 Confirm concentrations of
SA obtained from UV with
areas of peaks obtained
from HPLC
serum to the concentration
of the cosmetic product the
consumer has been
consecutively using
 Be sure to run controls
using animal serum and
various concentrations of
analyte
Sample Spectrum1,7
Conclusion
 Importance of usage of safe cosmetic products,




detection of SA in consumers is important to monitor
Practical analytical method as all compounds are able
to be detected, thus multiple analyte concentrations
may be compared
Fast detection and moderate cost
High levels of SA may cause serious long term health
effects
Salicylic acid is also an ingredient in asprin, how does
consumption of this drug compare affect serum levels,
is this also hazardous?
References
1. Francis; Taylor. Safety Assessment of Salicylic Acid, Butyloctyl Salicylate, Calcium Salicylate, C12–15 Alkyl Salicylate,
Capryloyl Salicylic Acid, Hexyldodecyl Salicylate, Isocetyl Salicylate, Isodecyl Salicylate, Magnesium Salicylate, MEA
Salicylate, Ethylhexyl Salicylate, Potassium Salicylate, Methyl Salicylate, Myristyl Salicylate, Sodium Salicylate, TEA
Salicylate, andTridecyl Salicylate. Int. J. of Tox. 2003, 22, 1-108.
2. Makino, K.; Itoh, Y. Determination of nonsteroidal anti-inflammatory drugs in human specimens by capillary zone
electrophoresis and micellar electrokinetic chromatography. Electrophoresis. 2004, 25, 1488–1495
3. Kasprzyk-Horden, B.; Dinsdale, R.; Guwy, A. Multiresidue methods for the analysis of pharmaceuticals,
personal care products and illicit drugs in surface water and wastewater by solid-phase extraction and ultra performance
liquid chromatography–electrospray tandem mass spectrometry. A. Bioanal Chem. 2008, 391,1293–1308.
4. http://www.sigmaaldrich.com/analytical-chromatography/analytical-products.html?TablePage=16706624
5. http://www.chem.agilent.com/en-US/Products/Instruments/lc/analytical/systems/120
0seriesbinarylc/Pages/default.aspx
6. Sarveiya, Vikram. Liquid chromatographic assay for common sunscreen agents: application to in vivo assessment of skin
penetration and systemic absorption in human volunteers. J. of Chrom. 2004, 803, 225-231.
7. Uges, D. An HPLC method for the determination of salicylic acid, phenacetin and paracetamol in serum, with indications;
two case-reports of intoxication. Int. Jour. Of Clin. Pharm. 2001. 3, 1309-1315.