Detection and localisation of small molecules
on skin using ambient mass spectrometry
Tara L Salter, Felicia M Green, Ian S Gilmore, Nilofar Faruqui
National Physical Laboratory, Teddington, UK.
Email: [email protected]
Introduction
Analysis of PCP ingredients
Detection of small molecules direct from skin or tissue is important for
development of novel health and personal care products. Understanding the
distribution of personal care product molecules in skin would be a valuable
tool for understanding adsorption and efficiency of the products.
14 key ingredients were individually analysed by DESI and PADI.
PADI
DESI
Mass spectrometry analysis of personal care products (PCPs) is largely
dominated by LC and GC-MS [1]. This involves lengthy extraction procedures
dependent on the molecules of interest. Ambient surface mass spectrometry
offers an alternative with minimal sample preparation and quick analysis.
The processes involved in PADI
ionisation and desorption lead to
complex ions forming which are not
as easy to identify as the molecular
ion. These ions can be losses,
additions or rearrangements of the
molecule.
Ambient mass spectrometry
Mass spectrometry is a powerful analytical technique with high chemical
specificity and sensitivity. Ambient MS enables the direct chemical analysis of
surfaces at atmospheric pressure.
DESI – Desorption Electrospray Ionisation
• Charged solvent droplets impact
the surface desorbing molecules
which are subsequently analysed
by a mass spectrometer.
• Used in a large range of
applications including
pharmaceutical and biomedical
analysis, forensics, homeland
security, tissue imaging and testing
of counterfeits in drugs and food.
DESI [2] mechanism
Structures of molecules successfully analysed by
each technique
• PADI successfully detects all molecules analysed, but spectra may be
difficult to interpret.
• DESI successfully analyses 64% of the molecules with simple spectra.
Analysis of PCPs on skin cells
A comparison of the similarities and differences between mass spectra from
different PCPs shows the ability to obtain useful information from each
technique.
All mass spectra are dominated by siloxanes, a common ingredient in PCPs
which act as a carrier and make the products have a silky smooth texture [1].
Cream 1
PADI – Plasma Assisted Desorption Ionisation
DESI
PADI
• An RF generated, atmospheric
non-thermal helium plasma is
used to desorb and ionise molecules
from the surface.
• PADI has successfully analysed
pharmaceuticals, plant materials
and polymers.
• Dn - cyclic polysiloxanes, (Si(CH3)2O)n
PADI [3] schematic
and in action
• Ln - linear polysiloxanes, CH3[Si(CH3)2O]nSi(CH3)3
Cream 2
DESI
PADI
Model skin systems & Personal Care Products (PCPs)
• Adult human dermal fibroblast (HDFa) cells
were cultured to confluence on sterile glass
microscope slides. This provided a uniform
monolayer of cells that was representative of
the surface of the skin.
• $250 billion is spent annually worldwide on
PCPs. Here, three off-the-shelf anti-ageing
creams from three different leading brands,
were deposited, without any dilution, onto the
cell surface using a swab.
• PADI mass spectrum gives rich information.
• Small molecules from PCPs identified – sunscreen agents, solvents and aromas.
Cream 3
DESI
PADI
Fluorescence confocal microscope
image of HDFa using the stains DAPI,
to visualise the nucleus, and Alexa
Fluor 488 conjugated phalloidin which
stains the actin filaments in the cell.
• PADI spectrum dominated by triethanolmaine, an emulsifier.
[1] R. Wang, R. P. Moody, D. Koniecki, J. Zhu, Environ. International, 2009, 35, 900
[2] Z. Takats, J. M. Wiseman, B. Gologan, R. G. Cooks, Science, 2004, 306, 471
• PADI and DESI MS can effectively analyse PCPs directly from skin cells,
with different information obtained from the two techniques.
[3] L. V. Ratcliffe, F. J. M. Rutten, D. A. Barrett, T. Whitmore, D. Seymour, C. Greenwood,
Y. Aranda-Gonzalvo, S. Robinson, M. McCoustra, Anal. Chem. 2007, 79, 6094
• Mass spectra are dominated by siloxanes, but also identify some small
active ingredients.
www.npl.co.uk/nanoanalysis