MACROIMS MACROION MOBILITY SPECTROMETER MOLECULAR WEIGHT AND PARTICLE SIZE DETERMINATION OF POLYVINYLPYRROLIDONE (PVP)

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1 MACROIMS MACROION MOBILITY SPECTROMETER MOLECULAR WEIGHT AND PARTICLE SIZE DETERMINATION OF POLYVINYLPYRROLIDONE (PVP) APPLICATION NOTE CHEMC-009 (A4) Polyvinylpyrrolidone (PVP) Polymer Polyvinylpyrrolidone (PVP) is a water-soluble polymer made from the monomer N-vinylpyrrolidone and is used in pharmaceutical and chemical applications. Typical molecular weights of PVP products are between 2 kda and over 2 MDa. This application note shows measurements with the TSI MacroIMS Macroion Mobility Spectrometer (MacroIMS) System as described below. Two PVP powders were purchased from Sigma: PVP10 with approximate mean molecular weight of 10 kda, and PVP360, with approx. mean molecular weight of 360 kda. Macroion Mobility Spectrometry for Molecular Weight and Size Determination The MacroIMS System is a versatile ion mobility spectrometry (IMS) system that relies on firstprinciple size analysis to determine the molecular weight of macromolecules and complexes between 8 kda and > 100 MDa. This technique reduces the breakdown of non-covalent interactions which usually accompany electrospray ionization through charge neutralization, allowing for analysis of macromolecular complexes. Separation of the intact, high mass macromolecules and complexes takes place in an ion mobility drift cell. The number of macromolecules is determined in each fraction by a single-macromolecule counter. The technique has been extensively reviewed in numerous citations, and a new development has enabled automated, high-throughput analysis and hyphenation options, making it applicable for routine laboratory applications. TSI and TSI logo are registered trademarks of TSI Incorporated. MacroIMS is a trademark of TSI Incorporated.

2 Sample Preparation PVP10 PVP10 powder (Sigma Aldrich, approx. average molecular weight 10 kda) was dissolved into 20 mm ammonium acetate buffer of ph approx. 6.8, resulting in a 3.39 mg/ml solution. The solution was vortexed until the PVP was completely dissolved. A dilution series was prepared using the same buffer, covering a concentration range of 42 nm to 3390 nm (0.42 µg/ml to 33.9 µg/ml, respectively). PVP360 PVP360 powder (Sigma Aldrich, approx. average molecular weight 360 kda) was dissolved into 20 mm ammonium acetate buffer of ph approx. 6.8 resulting in a 3.8 mg/ml solution. The solution was vortexed until the PVP was completely dissolved. A dilution series was prepared using the same buffer, covering a concentration range of 26 nm to 1056 nm (9.5 µg/ml to 380 µg/ml, respectively). Results In summary, molecular weight, polydispersity, and particle diameter have been determined for PVP10 and PVP360 for several concentrations. The signal response was found to be linear within a 95% confidence interval for the assessed concentrations. Table 1: Summary of basic polymer properties found for PVP10 and PVP360 measured with MacroIMS spectrometer. PVP10 PVP360 M p (kda) M n (kda) M w (kda) Polydispersity Diameter (D p ) (nm) Mp: Molecular weight in peak; Mn: number average molecular weight; Mw: weight average molecular weight; Dp: Diameter in peak The molecular weight found for PVP360 using the MacroIMS system would appear to be surprisingly low, and there are various factors that should be taken into account. Table 1 shows an M p of kda as the molecular weight in the peak of a count (number)-based distribution. The mass average molecular weight based on the measured distribution was determined to be approx kda. The size distribution of the PVP360 is very broad with a large tail preceding the main peak. Thus, when using a number-based measurement method like MacroIMS, the resulting molecular weight values are smaller than those derived from analytical methods that rely on separation interactions, optical properties, or mass dependent detection. -2-

3 Figure 1: Molecular weight distribution of PVP10 measured with the MacroIMS System at concentrations from 42 nm to 3390 nm. The scan range covered approx. 2 kda to 28 MDa. The molecular weight at the peak (M p ) was determined to be 12.1 kda. Polydispersity was calculated as approx. 2. Figure 2: Polymer size distribution of PVP10 measured with the MacroIMS System at concentrations from 0.42 µg/ml to 33.9 µg/ml. The scan range covered 2 nm to 55 nm. The particle diameter at the peak was determined to be 4.2 nm. -3-

4 Figure 3: Peak area integral of the PVP10 signal plotted versus the prepared concentration. Graph shows the 95% confidence interval. Figure 4: Molecular weight distribution of PVP360 measured with the MacroIMS System at concentrations from 26 nm to 528 nm. The scan range covered approx. 2 kda to 28 MDa. The molecular weight at the peak (M p ) was determined as kda. Polydispersity was calculated to be approx

5 Figure 5: Polymer size distribution of PVP360 measured with the MacroIMS System at concentrations from 10 µg/ml to 190 µg/ml. The scan range covered 2 nm to 55 nm. The particle diameter at the peak was determined to be 11.5 nm. Figure 6: Peak area integral of the PVP360 signal plotted versus the prepared concentration. Graph shows the 95% confidence interval. -5-

6 Discussion Knowing the size and molecular weight of polymers is of importance for developing pharmaceutical, chemical, cosmetic or other products with regards to bioavailability, drug stabilization, product stability, etc. Methods used to determine size and molecular weight may be biased by the performance of the separation technique used to fractionate the polydisperse polymers, and the detection method. The MacroIMS System performs separation of sizes in the gas-phase under atmospheric pressure, and therefore has no analyte-column material interaction dependence. The primary measurement of particle size is based on a first-order principle and requires no calibration. The detector delivers counts of polymer particles in the size fractions, and as such provides a truly number-based concentration determination. The size distribution obtained is independent of elution volumes. Thus the number-weighted size distribution may differ from calculated data using conventional methods. TSI Incorporated Visit our website for more information. USA Tel: UK Tel: France Tel: Germany Tel: India Tel: China Tel: Singapore Tel: CHEMC-009-A4 (9/3/2014) 2014 TSI Incorporated Printed in U.S.A.