FT-IR and Raman spectroscopic methods for identification and quantitation of orthorhombic and monoclinic paracetamol in powder mixes

FT-IR and Raman spectroscopic methods are suggested for identification of orthorhombic (form II) and monoclinic (form I) paracetamol and for their quantitative determination in mixes. The intensity ratio of the 836 cm(-1) FT-IR band (attributed to the presence of both forms) to the 806 cm(-1) monoclinic band plotted against the inverse monoclinic molar fraction (X) yields a straight line: I(836)/I(806)=0.515/X+0.700, r=0.9965 for eight calibration points on the regression line. Similarly, the area under the 454 cm(-1) band in FT-Raman spectra (which is attributed to both forms) over the area under the 465 cm(-1) band of monoclinic form is inversely related to its molar fraction (X): A(454)/A(465)=0.482/X-0.324, r=0.9954 for eight calibration points. Precision (RSD%) was <5% for both methods. Linear regression analysis between content and intensity of characteristic XRD reflections for four different samples gave r=0.9964 at 4.62 A and r=0.9894 at 3.70 A, for form II. For the content of form I, r=0.9596 at 3.37 A. The limit of detection for monoclinic form was estimated to be 0.012 mole fraction for both methods.     

Multivariate chemometric approach to thermal solid-state FT-IR monitoring of pharmaceutical drug compound

The study of thermal-related solid-state reaction monitored by spectroscopic method needs the use of advanced multivariate chemometric approach. It is because visual inspection of spectral data on particular functional groups or spectral bands is difficult to reveal the complete physical and chemical information. The spectral contributions from various species involved in the solid-state changes are generally highly overlapping and the spectral differences between reactant and product are usually quite minute. In this article, we demonstrate the use of multivariate chemometric approach to resolve the in situ thermal-dependent Fourier-transform infrared (FT-IR) mixture spectra of lisinopril dihydrate when it was heated from 24 to 170 degrees C. The collected FT-IR mixture spectra were first subjected to singular value decomposition (SVD) to obtain the right singular vectors. The right singular vectors were rotated into a set of pure component spectral estimates based on entropy minimization and spectral dissimilarity objective functions. The resulting pure component spectral estimates were then further refined using alternating least squares (ALS). In current study, four pure component spectra, that is, lisinopril dihydrate, monohydrate, anhydrate, and diketopiperazine (DKP) were all resolved and the relative thermal-dependent contributions of each component were also obtained. These relative contributions revealed the critical temperature for each transformation and degradation. This novel approach provides better interpretation of the pathway of dehydration and intramolecular cyclization of lisinopril dihydrate in the solid state. In addition, it can be used to complement the information obtained from differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).     

Thermal analysis of paracetamol polymorphs by FT-IR spectroscopies

A simple IR spectroscopy based methodology in routine screening studies of polymorphism is proposed. Reflectance and transmittance temperature-dependent IR measurements (coupled with the 2D-IR data presentation and the baseline analysis) offer a positive identification of each polymorphic phase, therefore allowing simple and rapid monitoring of the measured system. Applicability and flexibility of the methodology was demonstrated on the measurement of the model polymorphic compound paracetamol under various conditions (including geometric constraints and elevated pressure). The thermal behavior of paracetamol strongly depends on slight variations in experimental conditions that can result in formation of various phases (three polymorphs and the amorphous form). The amorphous phase can crystallize during heating into either Form II or Form III within almost identical temperature range. Likewise, the crystal transformations II → I and III → II also can proceed within almost identical temperature range. Furthermore, the thermal behavior is even more diverse than that, and includes the crystallizations of Forms I, II and III from the melt, and the high temperature II → I transition. The variety of the temperatures of the transformations is a major obstacle for unambiguous identification of a particular phase by DSC and a major reason for the implementation of these IR methods.     

FT-IR spectrophotometric analysis of dehydroepiandrosterone and its pharmaceutical formulation

A Fourier transform infrared (FT-IR) spectrometric method was developed for the rapid, direct measurement of dehydropeiandrosterone. Conventional KBr spectra and KBr + 2.0 mg microcrystalline cellulose (MCC) spectra were compared for best determination of active substance in drug formulation. Two chemometric approaches, partial least-squares (PLS) and principal component regression (PCR+) methods were used in data processing. The best results were obtained with PCR+ method.     

FT-IR and NMR spectroscopic studies of salicylic acid derivatives. I. Gentisamide -- a metabolite of salicylamide

Gentisamide (GAM, 2,5-dihydroxybenzamide), a minor first-pass metabolite of salicylamide (SAM, 2-hydroxybenzamide), was studied using FT-IR, 1D and 2D homo- and heteronuclear 1H and 13C NMR spectroscopy. GAM was isolated from human urine eight hours after oral administration of SAM. FT-IR, 1H and 13C NMR spectra unequivocally confirmed the chemical structure of GAM through chemical and substituent shifts, coupling constants and connectivities in COSY, NOESY, HETCOR and HBMC spectra. From NOESY spectra of GAM in DMSO-d6, it was concluded that the amide protons are oriented toward the ortho-proton at C-6. Obtained results indicate that the presence of the additional phenol group at C-5 in GAM favours the formation of intramolecular hydrogen bonding of the O...HO type between C2-OH proton and oxygen atom of the amide group.     

The use of low-resolution FT-IR spectrometry for the analysis of alcohols in breath

Fast and reliable diagnostic methods are needed for detection or exclusion of industrial solvents as a cause of intoxication. Analyzing human breath reveals the presence of any volatile substance. A portable Fourier transform infrared (FT-IR) multicomponent point-of-care analyzer was developed for exhaled breath. The analyzer proved to be accurate and precise in laboratory tests for simultaneous measurement of methanol and ethanol in water. Ethanol, in addition to normal contents of breath, was simultaneously analyzed in human experiments, and the results correlated well with blood samples. FT-IR method has a traceable calibration to physical properties of the analyte. The measured spectra can also be saved and analyzed later. Breath analysis with FT-IR is fast and easy, and no preparation of the sample is needed.     

Quantitative analysis of bucillamine and its pharmaceutical formulation using FT-IR spectroscopy

A Fourier transform infrared (FT-IR) spectrometric method was developed for the rapid, direct measurement of bucillamine. Conventional KBr-spectra and DRIFTS spectra were compared for best determination of active substance in its tablet formulation. Two chemometric approaches, partial least squares (PLS) and principal component regression (PCR+) methods were used in data processing. Similar results were obtained with both chemometric methods.     

Kinetic analysis of drug release from hydrogels containing amphoteric surfactants

A one compartment open model was used in order to describe chloramphenicol release from hydrogels containing amphoteric surfactants as gelling agents. Such interpretation seems to be more profitable than that based on Higuchi's root square equation. Using the proposed model it is possible to consider that drug release takes place from the water phase near the surface of membrane, rather than from the micellar phase in which drug seems to be immobilized.     

Feasibility of using GC/FT-IR for drug analysis in the forensic toxicology laboratory.

New developments in cryogenic sample deposition for gas chromatography/Fourier transform infrared (GC/FT-IR) spectroscopy have increased the sensitivity of the technique 100-1000-fold, to match or surpass that of gas chromatography/mass spectrometry (GC/MS). The current methods of GC/MS have led to some false positive identifications in drug testing labs. New methods employing GC/FT-IR will provide absolute identification through infrared fingerprinting with routine detection in the ppb range. GC/FT-IR methods are being developed which indicate low picogram amounts of material are detectable. Some preliminary data have shown that reference-quality spectra can be obtained from samples containing 200 ng/mL of amphetamines, and spectra from samples below the 25 ng/mL level for amphetamines can be obtained for identification purposes. These and other applications will be addressed along with limit of detection (LOD), limit of quantitation (LOQ), and linearity in comparison to commonly used techniques.     

Clotrimazole-loaded nanostructured lipid carrier hydrogels: Thermal analysis and in vitro studies

The aim of the present work is to design a new formulation containing clotrimazole (CTZ) loaded into nanostructured lipid carriers (NLC) for the treatment of fungal vaginal infections. In order to obtain formulations with suitable viscosity for mucosal application, NLC containing CTZ produced by the ultrasonication method were viscosized by the addition of poloxamer P407 in the NLC dispersion (CTZ-NLC-gel). These systems exhibit well-known thermogelling properties. The rheological characterization of the CTZ-NLC hydrogel using a controlled stress rheometer evidenced that the presence of NLC or CTZ did not affect gelling temperature (T_gel). Dilution with simulated vaginal fluid (SVF) increased the T_gel from 17.4 to 29.6 °C. For these thermogelling systems, micro-calorimetric assays conducted by a Micro-DSC III confirmed that the hydrogel-containing CTZ-NLC was able to change its structure with a rapid passage from non-crystalline (liquid) to crystalline (semi-solid) form. Furthermore, when a local application is considered, no drug should pass through the vaginal mucosa, limiting thus the systemic diffusion and toxicity. For this purpose, Franz cell has been employed to investigate the ex vivo permeation of CTZ through pig vaginal mucosa. The results showed no CTZ diffusion. The toxicological experiments performed on HeLa cells after a 24 h incubation time confirmed that CTZ-NLC-gel at a concentration of 1 mg/mL showed a low toxicity profile resulting in a cell vitality of 77.2%. Interestingly, anti-candida activity studies demonstrated that CTZ-NLC gel was 4-fold more active than Fungizone^® against Candida albicans. These encouraging results suggest that the hydrogel containing CTZ-NLC could be proposed as an innovative system to administer CTZ to treat vaginal infections.     

Solid surface spectroscopic methodology for ultra-trace urinary nickel monitoring in smokers and non-smokers’ subjects

Nickel chemical enrichment on nylon membranes previously treated with eosin (eo) is proposed for subsequent quantification by spectrofluorimetry (λ_em = 547 nm, λ_exc = 515 nm). Operational variables which have influence on quantitative metal retention have been studied. At optimal experimental conditions, quantitative recovery was reached (superior to 99%), with a detection limit of 0.13 ng L⁻¹ and quantification limit of 0.44 ng L⁻¹. The calibration sensitivity was of 6 × 10¹³ ng L⁻¹ for the new methodology with a linear range of 0.44–410 ng L⁻¹ Ni(II). The tolerance levels, respect to cations and anions as potential interferents, were studied, with good results. The methodology was validated by standard addition method and satisfactorily applied to urinary nickel determination of 50 subjects including smokers, second hand smokers and non-smokers’ samples without previous treatment. Stability of biological samples was daily studied for a period of 1 month. Within-day precision was better than 0.02 CV. The reproducibility (between-day precision) was also evaluated over 3 days by performing six determinations each day with a CV of 0.052. The different groups were evaluated using one-way analysis of variance (ANOVA) followed by Tukey–Kramer multiple comparison test with satisfactory results.     

Laser Raman spectroscopic analysis of polymorphic forms in microliter fluid volumes

Knowledge and control of the polymorphic phase of chemical compounds are important aspects of drug development in the pharmaceutical industry. We report herein in situ and real-time Raman spectroscopic polymorphic analysis of optically trapped microcrystals in a microliter volume format. The system studied in particular was the recrystallization of carbamazepine (CBZ) in methanol. Raman spectrometry enabled noninvasive measurement of the amount of dissolved CBZ in a sample as well as polymorphic characterization, whereas exclusive recrystallization of either CBZ form I or CBZ form III from saturated solutions was achieved by specific selection of sample cell cooling profiles. Additionally, using a microcell versus a macroscopic volume gives the advantage of reaching equilibrium much faster while using little compound quantity. We demonstrate that laser Raman spectral polymorphic analysis in a microliter cell is a potentially viable screening platform for polymorphic analysis and could lead to a new high throughput method for polymorph screening.     

近红外光谱法在桂利嗪片快速分析中的应用

目的利用近红外光谱(NIR)技术建立快速鉴别桂利嗪片的一致性检验模型和特征谱段相关系数模型。方法以桂利嗪片为对象,采用光纤探头测定样品近红外光谱,通过一致性指数(CI)值和一致性指数限度比较法建立一致性检验模型;通过在特征谱段选择合适的相关系数(r)值为阈值建立相关系数模型。结果建立的一致性检验模型和特征谱段相关系数模型均可快速鉴别并准确区分桂利嗪片(辰欣药业股份有限公司)与其他生产厂家的同类产品;验证样品的一致性指数值均>7.0,相关系数均<97%。结论方法快速、简便,可用于桂利嗪片的现场快速筛查。     

FT-IR and NMR spectroscopic studies of salicylic acid derivatives. II. Comparison of 2-hydroxy- and 2,4- and 2,5-dihydroxy derivatives

The 2,4- and 2,5-dihydroxybenzamides (8, 9) were synthesized from their corresponding methyl esters. The structures and the spectral properties of investigated salicylic acid (1), 2,4- and 2,5-dihydroxy benzoic acids (2, 3), their methyl esters (4-6) and amides (7-9) were analyzed by means of FT-IR and one- and two-dimensional homo- and heteronuclear 1H and 13C NMR spectroscopies. Comparison of FT-IR and NMR spectral data of investigated compounds showed that the spectral characteristics of 2,4-dihydroxy benzoic acid derivatives are more similar to those of 2-hydroxy benzoic acid (salicylic acid) derivatives than to those of 2,5-dihydroxy benzoic acid derivatives. The results suggest that the spatial orientation of amide protons in 2,4-dihydroxy benzamide resembles more that in salicylamide than that in 2,5-dihydroxy benzamide.