# In Situ Focused Beam Reflectance Measurement (FBRM), Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) and Raman Characterization of the Polymorphic Transformation of Carbamazepine

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Material and Methods

#### 2.1. Preparation of Pure Carbamazepine Polymorphs

#### 2.2. Polymorphic Transformation during Seeded Isothermal Crystallization

## 3. Results and Discussion

#### 3.1. Characterization of Carbamazepine Polymorphs

^{−1}was subtracted from absorbance intensity peak heights at 1400 and 1677 cm

^{−1}. The calibration model is:

_{exp}is the CBZ concentration calculated from the ATR-FTIR measurements. P

_{1251}, P

_{1400}, and P

_{1677}are the intensity values of absorbance peaks at 1251, 1400, and 1677 cm

^{−1}, respectively. To check the veracity of this model, some comparisons between the known concentrations and those calculated from the calibration model at different temperatures are shown in Figure 4 and Table 1, indicating that the concentration obtained from the calibration model can accurately represent the actual solute concentration to within a 95% measurement error of ±3.6%.

T/°C | C_{act}/g ∙ (g 1-propanol)^{−1} | C_{cal}/g ∙ (g 1-propanol)^{−1} | |
---|---|---|---|

25.0 | 0.0177 | 0.0181 | 0.018 |

43.0 | 0.0329 | 0.0337 | 0.023 |

40.0 | 0.0352 | 0.0355 | 0.008 |

47.0 | 0.0376 | 0.0377 | 0.003 |

46.0 | 0.0377 | 0.0377 | 0.001 |

45.0 | 0.0379 | 0.0386 | 0.017 |

49.0 | 0.0455 | 0.0446 | 0.020 |

50.0 | 0.0515 | 0.0498 | 0.033 |

56.0 | 0.0531 | 0.0522 | 0.016 |

54.0 | 0.0550 | 0.0554 | 0.006 |

50.0 | 0.0556 | 0.0552 | 0.006 |

58.0 | 0.0666 | 0.0667 | 0.002 |

#### 3.2. Solubility of Carbamazepine Polymorphs

_{s}. The solute concentration at this temperature was calculated by the FTIR model and was considered to be the solubility at T

_{s}, which is shown in Figure 5 and Table 2. Because of transformation problems, the solubility of Form II could not be determined below 40 °C. The thermodynamic relationship between the two polymorphic forms was determined by plotting the solubility data using a quadratic equation. A transition point T

_{t}between the two polymorphic forms was evaluated at 34.2 °C by extending the quadratic fitting trend line of the Form II solubility. The fact that a transition point exists below the melting point of CBZ (191–192 °C) confirms that the two forms are enantiotropically related. At the transition temperature point the solubilities of the two forms are the same. The solubility of Form III is higher than that of Form II in 1-propanol above the transition temperature, while below the transition temperature, the solubility of Form III is lower than that of Form II.

**Figure 5.**The solubility-temperature diagram and fitting curves for carbamazepine of Forms II and III.

T/°C | Solubility of Form II/g ∙ (g 1-propanol) ^{−1} | T/°C | Metastable limit of Form II/g ∙ (g 1-propanol) ^{−1} | T/°C | Solubility of Form III/g ∙ (g 1-propanol) ^{−1} | T/°C | Metastable limit of Form III/g ∙ (g 1-propanol) ^{−1} |
---|---|---|---|---|---|---|---|

39.7 | 0.0318 | 39.2 | 0.04777 | 25.0 | 0.0196 | 22.0 | 0.03407 |

45.0 | 0.03796 | 45.9 | 0.06155 | 29.3 | 0.02485 | 27.7 | 0.03909 |

48.0 | 0.04215 | 52.3 | 0.07261 | 34.0 | 0.02909 | 34.2 | 0.04595 |

53.4 | 0.05077 | 58.0 | 0.08335 | 40.5 | 0.03831 | 38.5 | 0.04806 |

58.6 | 0.06267 | -- | -- | 48.5 | 0.05267 | -- | -- |

-- | -- | -- | -- | 52.3 | 0.06111 | -- | -- |

-- | -- | -- | -- | 58.0 | 0.07252 | -- | -- |

-- | -- | -- | -- | 60.0 | 0.08632 | -- | -- |

-- | -- | -- | -- | 64.0 | 0.09961 | -- | -- |

#### 3.3. Metastable Limits of Carbamazepine Polymorphs

_{l}, and the concentration was determined by FTIR, which was defined as the primary metastable limit at T

_{l}. Figure 6 and Table 3 show the metastable limits. There was a point of intersection at 39.9 °C of the quadratic fitting curves for CBZ metastable limits of Forms II and III. It can be inferred that, Form II will be inclined to nucleate if only primary nucleation happened above the intersection point. On the contrary, Form III tends to nucleate below the intersection point.

Parameters | A | B | R^2 |
---|---|---|---|

values | 9.71 × 10^{−6} | 7.51 × 10^{−4} | 0.998 |

error | 3.87 × 10^{−6} | 0.545 × 10^{−4} |

#### 3.4. Quantitative Analysis of Polymorphic Transformation

^{−1}and 1450 cm

^{−1}for the Form III and Form II respectively can be readily observed. These Raman peaks are relatively sensitive to the changes in weight ratios between Form III and Form II. As discussed in the literatures [6,8], the Raman intensities depend not only on the concentration of individual polymorphic forms but also on the overall solid content, particle size of the solid phases and temperature in the mixtures. The intensity at 1271 cm

^{−1}was found to be suitable for background to reduce these effects. The following equation and corresponding regression parameters in Table 3 were used to quantify the polymorphs during the polymorphic transformation process. In equation 2, H represents the Raman intensity of each peak, Y represents the mass fraction of solid Form II in suspension. To reduce the effect of the overall solids concentration and solution content, the results were divided by the calculated value of pure form II in each run.

#### 3.5. Real-Time Monitoring of Polymorphic Transformation of Carbamazepine during Seeded Isothermal Crystallization

Run Number | Initial solution concentration (g/g 1-propanol) | Supersaturation for Form III (g/g) | Relative seed mass of Form II (g Form II/g solute) |
---|---|---|---|

1 | 0.0275 | 0.2791 | 7% |

2 | 0.0275 | 0.2791 | 10% |

3 | 0.0275 | 0.2791 | 15% |

#### 3.5.1. FBRM Results of Polymorphic Transformation in Seeded Isothermal Crystallization

**Figure 9.**SEM picture of the sample taken at 20 min in Run 2. Crystals 1 and 2 are considered to be Form II and 3-6 as Form III.

#### 3.5.2. Raman and FTIR Results of the Polymorph Transformation in Seeded Isothermal Crystallization

**Figure 10.**The comparison between the concentration profiles measured by ATR-FTIR during Runs 1, 2 and 3.

_{II}and A

_{III}are the total surface area of Form II and Form III crystals in vessel respectively; ρ

_{II}and ρ

_{III}are the crystal densities; C represents the concentration of CBZ in solution, g/g 1-propanol; P is the mass of 1-propanol in solution in vessel. The dissolution rate for Form II and precipitation rate for Form III may be described by the following power-law expressions:

^{−2}s

^{−1}; k

_{R}and k

_{G}are rate coefficients respectively. If it is assumed that A

_{II}and A

_{III}are constant with time (a sweeping assumption) and both the dissolution and growth processes are first order (r = 1; g = 1), substituting Equation (4) and Equation (5) into Equation (3) and integrating gives:

_{II}and thus a would increase and so the concentration would fall faster for higher amounts of seed, as shown in Figure 10. Note that by assuming A

_{II}and A

_{III}do not very with time, the model is highly approximate. The ratio of the two forms suspended in the solution can also be calculated from Raman spectra and compared with Figure 11. From Figure 8,Figure 9,Figure 10,Figure 11, we can conclude that the nucleation of Form III started immediately after Form II seeds were added in the saturated solution and the dissolution of Form II seeds followed thereafter.

## 4. Conclusions

## References

- Chapman, D. The polymorphism of glycerides. Chem. Rev.
**1962**, 62, 433–456. [Google Scholar] - Fried, E.; Gurtin, M.E. Dynamic solid-solid transitions with phase characterized by an order parameter. Phys. D
**1994**, 72, 287–308. [Google Scholar] - Cardew, P.; Davey, R. The kinetics of solvent-mediated phase transformations. Proc. R. Soc. Lond. A
**1985**, 398, 415–428. [Google Scholar] - O’Sullivan, B.; Barrett, P.; Hsiao, G.; Carr, A.; Glennon, B. In situ monitoring of polymorphic transitions. Org. Process Res. Dev.
**2003**, 7, 977–982. [Google Scholar] [CrossRef] - O’Sullivan, B.; Glennon, B. Application of in situ FBRM and ATR-FTIR to the monitoring of the polymorphic transformation of D-mannitol. Org. Process Res. Dev.
**2005**, 9, 884–889. [Google Scholar] - Ono, T.; Ter Horst, J.; Jansens, P. Quantitative measurement of the polymorphic transformation of L-glutamic acid using in-situ Raman spectroscopy. Cryst. Growth Des.
**2004**, 4, 465–469. [Google Scholar] - Tian, F.; Zeitler, J.A.; Strachan, C.J.; Saville, D.J.; Gordon, K.C.; Rades, T. Characterizing the conversion kinetics of carbamazepine polymorphs to the dihydrate in aqueous suspension using Raman spectroscopy. J. Pharm. Biomed. Anal.
**2006**, 40, 271–280. [Google Scholar] - Chen, Z.P.; Fevotte, G.; Caillet, A.; Littlejohn, D.; Morris, J. Advanced calibration strategy for in situ quantitative monitoring of phase transition processes in suspensions using FT-Raman spectroscopy. Anal. Chem.
**2008**, 80, 6658–6665. [Google Scholar] - Vankeirsbilck, T.; Vercauteren, A.; Baeyens, W.; van der Weken, F. Applications of Raman spectroscopy in pharmaceutical analysis. TrAC Trends Anal. Chem.
**2002**, 21, 869–877. [Google Scholar] - Liu, W.; Wei, H.; Black, S. An investigation of the transformation of carbamazepine from anhydrate to hydrate using in situ FBRM and PVM. Org. Process Res. Dev.
**2009**, 13, 494–500. [Google Scholar] - Hartley, R.; Aleksandrowicz, J.; Ng, P.; McLain, B.; Bowmer, C.; Forsythe, W. Breakthrough seizures with generic carbamazepine: a consequence of poorer bioavailability? Br. J. Clin. Pract.
**1990**, 44, 270–273. [Google Scholar] - Edwards, A.D.; Shekunov, B.Y.; Kordikowski, A.; Forbes, R.T.; York, P. Crystallization of pure anhydrous polymorphs of carbamazepine by solution enhanced dispersion with supercritical fluids (SEDS™). J. Pharm. Sci.
**2001**, 90, 1115–1124. [Google Scholar] - Yoshihashi, Y.; Yonemochi, E.; Terada, K. Estimation of initial dissolution rate of drug substance by thermal analysis: Application for carbamazepine hydrate. Pharm. Dev. Technol.
**2002**, 7, 89–95. [Google Scholar] - Burger, A.; Ramberger, R. On the polymorphism of pharmaceuticals and other molecular crystals. I: Theory of thermodynamic rules. Microchim. Acta
**1979**, 72, 259–271. [Google Scholar] [CrossRef] - Ostwald, W. Studies of the formation and transformation of solid substances. Phys. Chem.
**1897**, 22, 289. [Google Scholar] - Kaneko, F.; Sakashita, H.; Kobayashi, M.; Suzuki, M. Infrared spectroscopic and chemical etching study on the crystallization process of the B and E forms of stearic acid: Roles of dislocations in single crystals. J. Phys. Chem.
**1994**, 98, 3801–3808. [Google Scholar] - Brittain, H.G. Polymorphism in Pharmaceutical Solids; Marcel Dekker, Inc.: New York, NY, USA, 1999; Volume 95. [Google Scholar]
- McCrone, W.C. “Polymorphism,” Chapter 8 in Physics and Chemistry of the Organic Solid State; Fox, D., Labes, M.M., Weissberger, A., Eds.; Interscience: New York, NY, USA, 1965; Volume 11. [Google Scholar]
- Grzesiak, A.L.; Lang, M.; Kim, K.; Matzger, A.J. Comparison of the four anhydrous polymorphs of carbamazepine and the crystal structure of form I. J. Pharm. Sci.
**2003**, 92, 2260–2271. [Google Scholar] - Mao, S.; Zhang, Y.; Rohani, S.; Ray, A.K. Kinetics of (R, S)-and (R)-mandelic acid in an unseeded cooling batch crystallizer. J. Cryst. Growth
**2010**, 312, 3340–3348. [Google Scholar]

© 2012 by the authors; licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).

## Share and Cite

**MDPI and ACS Style**

Zhao, Y.; Bao, Y.; Wang, J.; Rohani, S.
*In Situ *Focused Beam Reflectance Measurement (FBRM), Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) and Raman Characterization of the Polymorphic Transformation of Carbamazepine. *Pharmaceutics* **2012**, *4*, 164-178.
https://doi.org/10.3390/pharmaceutics4010164

**AMA Style**

Zhao Y, Bao Y, Wang J, Rohani S.
*In Situ *Focused Beam Reflectance Measurement (FBRM), Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) and Raman Characterization of the Polymorphic Transformation of Carbamazepine. *Pharmaceutics*. 2012; 4(1):164-178.
https://doi.org/10.3390/pharmaceutics4010164

**Chicago/Turabian Style**

Zhao, Yingying, Ying Bao, Jingkang Wang, and Sohrab Rohani.
2012. "*In Situ *Focused Beam Reflectance Measurement (FBRM), Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) and Raman Characterization of the Polymorphic Transformation of Carbamazepine" *Pharmaceutics* 4, no. 1: 164-178.
https://doi.org/10.3390/pharmaceutics4010164