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 Pain relief medicine (analgesic)

Surface Spectroscopy on Pain Management Drugs with EnviroESCA

The global market for pain management drugs and devices is expected to reach over 40 billion USD in 2017. In this study we had an exemplary look on two typical pain relief tablets to study their surface chemistry.

X-ray photoelectron spectroscopy (XPS) is an extremely surface sensitive technique where the sample is illuminated with X-ray radiation of a specific energy. The emitted photoelectrons originate from the uppermost surface layers. Their energies are specific to the elements in atoms or molecules of which they escaped. When X-ray photons hit atoms in deeper layers of the surface the released electrons will be absorbed by the upper layers and cannot contribute to the measurement signal. Therefore the XPS information depth is limited to the outermost 10nm. Classical XPS systems are operated with the sample in ultra-high vacuum conditions, not being compatible with most biological materials.

Two common pain relief medicines were chosen for analysis, namely Acetylsalicylic Acid and Ibuprofen. The former one is white and the latter one is orange coloured.

Pharmaceutical Drugs

In the following measurement data is presented that was taken on different position on the pills. The drugs under investigation were cleaved so that the inner and the outer surface of each pill were accessible.
The samples were cleaved and positioned on the sample plate using carbon tape directly before analysis without any additional pre-treatment, drying, or cleaning procedure. The Sample Environment was pumped down to 2 mbar of an Argon atmosphere and the sample was placed in front of the analysers nozzle and the X-ray window.

 
Results
1. Acetylsalicylic Acid

Acetylsalicylic Acid
 

The images were recorded with one of the three digital microscopes in the EnviroESCA Analysis Module. The metal pipe coming from the lower left corner allows for dosing of gases directly onto the analysed region of the sample.
 The chemical structure of Acetylsalicylic Acid  

Pharmaceutical Drug under EnviroESCA nozzle

Pharmaceutical Drug under EnviroESCA nozzle
Position 1: inside of the pill  Position 2: outside surface


The C1 s and O 1s high-resolution spectra from the inside of the Acetylsalicylic Acid pill show typical signatures of a benzoic acid derivative with an additional acetyl substituent, which are located at 285.0 eV (CC/CH), 286.7 eV (C-O), 289.3 eV (COO), 532.4 eV (O=C), and 533.9 eV (O-C).

XPS Spectra of Acetylsalicylic Acid taken with EnviroESCA

 XPS Spectra of Acetylsalicylic Acid taken with EnviroESCA
 XPS Spectra of Acetylsalicylic Acid taken with EnviroESCA
 XPS Spectra of Acetylsalicylic Acid taken with EnviroESCA
Typically these pain relief pills contain much more than just the active ingredient, e.g. Acetylsalicylic Acid or Ibuprofen. Further ingredients are needed to hold the pill together others are added to help the pill to break up, or disintegrate, after being taken. Additionally, pain relief pharmaceutical drugs often consist of a core and a coat. The coat contains sugar, e.g. sucrose, for taste and a pigment to give the pill an acceptable colour.
That coating is reflected in the C 1 score-level spectrum, which resembles very much that of a sugar with a predominant C-O component at 286.6 eV together with other peak components located at 285.0 eV, 288.0 eV, and 289.4 eV originating from carbon atoms of hydrocarbons (CC/CH), acetal or carbonyl (O-C-O, C=O), and carboxyl (COO) moieties.
So the C1s and O 1s high-resolution spectra taken on the inside of the cleaved pill look totally different compared to the ones obtained from the pills outside.
 
2. Ibuprofen

Ibuprofen

The images were recorded with one of the three digital microscopes in the EnviroESCA Analysis Module. The metal pipe coming from the lower left corner allows for dosing of gases directly onto the analysed region of the sample.
 The chemical structure of Ibuprofen  
 Ibuprofen under the analyzer nozzle of EnviroESCA   Ibuprofen under the analyzer nozzle of EnviroESCA
 Position 1: inside of the pill  Position 2: outside surface

Ibuprofens C1 s and O 1s high-resolution spectra taken at the inside of the pill show typical signatures of a carboxylic acid derivative with an aromatic substituent, which are located at 285.0 eV (CC/CH), 285.9 eV (C-COO/C-O/C-N), 287.4 eV (C=O, O-C-O), 289.5 eV (COO), 532.3 eV (O=C), and 533.6 eV (O-C).
Similar to the Acetylsalicylic Acid pill the C1s high-resolution spectrum of the Ibuprofen pills outside indicates a sugar-based surface coating.
 XPS Spectra of Ibuprofen taken with EnviroESCA
XPS Spectra of Ibuprofen taken with EnviroESCA
 XPS Spectra of Ibuprofen taken with EnviroESCA
XPS Spectra of Ibuprofen taken with EnviroESCA
 
Conclusion:
EnviroESCA has shown its ability to analyze the surfaces of common pain relief medicine with XPS. Standard ultra high vacuum based ESCA systems can often  not be applied to this kind of studies because of the high vapor pressure of many drugs. Near Ambient Pressure XPS (NAP-XPS) can easily be applied to pharmaceutical materials and drugs just out of the package. The surface analysis of two different analgesics reveals spectral signatures of the respective active ingredients, Acetylsalicylic Acid or Ibuprofen. Moreover, it could be demonstrated that the (outermost) surface layer of the analyzed pills is predominantly composed of a sugar coating.



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