G. Manoj Kumar

Laser-induced breakdown spectroscopy-based investigation and classification of pharmaceutical tablets using multivariate chemometric analysis

We report the effectiveness of laser-induced breakdown spectroscopy (LIBS) in probing the content of pharmaceutical tablets and also investigate its feasibility for routine classification. This method is particularly beneficial in applications where its exquisite chemical specificity and suitability for remote and on site characterization significantly improves the speed and accuracy of quality control and assurance process. Our experiments reveal that in addition to the presence of carbon, hydrogen, nitrogen and oxygen, which can be primarily attributed to the active pharmaceutical ingredients, specific inorganic atoms were also present in all the tablets. Initial attempts at classification by a ratiometric approach using oxygen (∼777 nm) to nitrogen (742.36 nm, 744.23 nm and 746.83 nm) compositional values yielded an optimal value at 746.83 nm with the least relative standard deviation but nevertheless failed to provide an acceptable classification. To overcome this bottleneck in the detection process, two chemometric algorithms, i.e. principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA), were implemented to exploit the multivariate nature of the LIBS data demonstrating that LIBS has the potential to differentiate and discriminate among pharmaceutical tablets. We report excellent prospective classification accuracy using supervised classification via the SIMCA algorithm, demonstrating its potential for future applications in process analytical technology, especially for fast on-line process control monitoring applications in the pharmaceutical industry.

One-Dimensional Discrete Combustion Waves in Periodical and Random Systems

The authors consider propagation of burn wave along a one-dimensional system of point heat sources connected by inert heat-conducting elements for periodical and disordered systems. Dependence of burn rate of such systems on burn temperature is determined. It is shown that under certain conditions a steady-state combustion mode in periodical systems becomes unstable and it is replaced by oscillatory modes, which consistently lose stability in the form of doubling period bifurcations. It is established that the burn rate of disordered system is many times less than the burn rate of a periodical system at identical average parameters. Results of modeling are compared with experimental data on combustion of thermite systems.

Experimental studies of spontaneous emission from dopants in an absorbing dielectric

We report the first measurements, to our knowledge, of the modification of spontaneous emission rates of Eu3+ ions in the visible region owing to an absorbing medium. Precise levels of the absorption coefficient are introduced by codoping with different amounts of Nd3+. We use a binary glass system PbO-B2O3 as the host, the compositional variation of which leads to a change in the real part of the refractive index. Measured lifetimes are found to follow the real cavity model, and the data are analyzed by the model proposed by Scheel et al. [Phys. Rev. A 60, 4094 (1999)]. We give estimates of the parameter that is related to the radius of the cavity around Eu3+.

Stoichiometric analysis of ammonium nitrate and ammonium perchlorate with nanosecond laser induced breakdown spectroscopy

We present our results on the stoichiometric analysis of ammonium nitrate (AN) and ammonium Perchlorate (AP) studied using laser induced breakdown spectroscopy (LIBS) with nanosecond pulses. The LIBS spectra collected for AP and AN, without any gating and using a high resolution spectrometer, exhibited characteristic lines corresponding to O, N, H, C, and K. The Oxygen line at 777.38 nm and three Nitrogen lines (N1, N2, N3) at 742.54 nm, 744.64 nm, 747.12 nm were used for evaluating the Oxygen/Nitrogen ratios. The intensities were calculated using area under the peaks and normalized to their respective transition probabilities and statistical weights. The O/N1 ratios estimated from the LIBS spectra were ~4.94 and ~5.11 for AP and O/N3 ratios were ~1.64 and ~1.47 for AN obtained from two independent measurements. The intensity ratios show good agreement with the actual stoichiometric ratios - four for AP and one for AN.

Laser-induced breakdown spectroscopy of RDX and HMX with nanosecond, picosecond, and femtosecond pulses

Herein we present some of our initial experimental results obtained from the laser induced breakdown spectroscopic (LIBS) measurements of RDX and HMX using nanosecond (ns), picosecond (ps), and femtosecond (fs) laser pulses acquired without gating and delay. RDX and HMX were mixed with KBr and pellets were prepared for the spectroscopic studies. Nanosecond pulses at 532 nm, ps/fs pulses at 800 nm were used for the experiments. The spectra were collected using Ocean Optics 4000/Maya spectrometer using a UV transmitting, 400 μm core diameter fiber in one case and a combination of lenses to collect the light from plasma in the second case. Several features were observed in the spectra exclusive for each pulse domain. The differences/similarities in the spectra collected using different pulses are presented.

Investigation of molecular and elemental species dynamics in NTO, TNT, and ANTA using femtosecond LIBS technique

We present our initial experimental results from the LIBS studies of pyrazole, 1-nitropyrazole, 3-nitropyrazole, 3,4- dinitropyrazole and 1-methyl- 3,4,5 trinitro pyrazole recorded with femtosecond pulses and performed in argon atmosphere. CN molecular bands in three different spectral regions of 357 nm-360 nm, 384 nm-389 nm and 414 nm -423 nm, C2 swan bands near 460 nm-475 nm, 510 nm– 520 nm and 550 nm-565 nm were observed. The C peak at 247.82 nm, H peak at 656.2 nm have also been observed along with several peaks of O and N. CN/C2, CN/C, C2/C and C2/N ratios were measured from the average of 25 spectra obtained in argon. The effect of number of nitro groups on the atomic and molecular emission has been evaluated. A gate delay of 100 ns and a gate width of 800 ns were used for collecting the spectra.

Discrimination methodologies using femtosecond LIBS and correlation techniques

Laser induced breakdown spectroscopy is an attractive and versatile spectroscopic technique employed successfully for the detection of hazardous substances. The specific advantages of using femtosecond (fs) pulses with LIBS technique include lower ablation threshold, reduced background Continuum emission. In addition to atomic peaks in plasma the molecular peaks (CN and C2) also play a significant role in classification of these samples. In the present work fs LIBS spectra were recorded from five different samples (RDX, HMX, NTO, ANTA, and DADNE) made in the form of pure pellets. Correlation statistics were used to discriminate the samples based on molecular, atomic ratios. This paper discusses, in detail, a simple correlation technique applied for the fs LIBS data for achieving classification.

Femtosecond LIBS studies of Nitropyrazoles

We present our initial experimental results from the LIBS studies of pyrazole, 1-nitropyrazole, 3-nitropyrazole, 3,4- dinitropyrazole and 1-methyl- 3,4,5 trinitro pyrazole recorded with femtosecond pulses and performed in argon atmosphere. CN molecular bands in three different spectral regions of 357 nm-360 nm, 384 nm-389 nm and 414 nm -423 nm, C2 swan bands near 460 nm-475 nm, 510 nm– 520 nm and 550 nm-565 nm were observed. The C peak at 247.82 nm, H peak at 656.2 nm have also been observed along with several peaks of O and N. CN/C2, CN/C, C2/C and C2/N ratios were measured from the average of 25 spectra obtained in argon. The effect of number of nitro groups on the atomic and molecular emission has been evaluated. A gate delay of 100 ns and a gate width of 800 ns were used for collecting the spectra.

Dynamic response of metals and alloys to laser-induced shock waves

We present the measurements on the propagation characteristics of the laser generated acoustics shock waves and the vibrations inside material targets from laser-metal interaction in real time. Laser pulses (7 ns) from second harmonic of a Nd: YAG laser (532 nm) were used to launch compression waves inside the solid samples. The acoustic measurements were carried out using a calibrated microphone, while the vibrations induced within the material before getting converted into ASW in the atmosphere were measured using vibration transducers (piezoelectric accelerometer). The arrival time of the vibration transducer was used to measure the particle velocity within the material that increased with increasing laser energy. The measurement of the arrival time of the ASW as a function of the microphone distance from the source of explosion was carried out. The shock velocity with respect to distance from the source of explosion followed an exponential decay. The arrival time of the ASWs was found to be increasing with the distance. The shock arrival time with respect to incident laser energy showed an exponential decay where as the shock velocity was found to be linearly increasing with the incident laser energy. Overall, acoustic energy has increased with increasing density of the material.