N. Bouropoulos

Use of Raman Spectroscopy for the Quantitative Analysis of Calcium Oxalate Hydrates: Application for the Analysis of Urinary Stones

The potential use of the Raman spectroscopy (RS) for the quantitative analysis of the mineral components of urinary stones consisting mainly of the mono- and dihydrate salts of calcium oxalate has been demonstrated. The quantitative analysis was based on the construction of calibration curves made of known mixtures of synthetically prepared pure calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD). The Raman spectra of well-mixed powdered samples of COM and COD were recorded, and the characteristic bands at 1462 and 1477 cm−1 for COM and COD, respectively, were used as the basis for the quantitative analysis. It was found that xM = (IR – 0.134)/(0.8IR + 1.52), where xM is the molar fraction of COM in the solid mixture and IR represents the intensity ratio of the Raman band at 1462 cm−1 to that of 1477 cm−1. The calibration curve was used for the analysis of a typical urinary stone surgically removed, and it was found that xM = 0.33. This finding was confirmed by infrared quantitative spectroscopic analysis. Quantitative analysis using the proposed Raman technique had a detection limit of approximately 0.6 mol % content in COM. The relative advantage of RS lies in its potential use as a nondestructive analytical technique for the mineral composition of urinary stones.

Urinary Stone Layer Analysis of Mineral Components by Raman Spectroscopy, IR Spectroscopy, and X-ray Powder Diffraction: A Comparative Study

Mineral components of a urinary stone forming layers have been analyzed with the use of Raman spectroscopy (RS), Fourier transform infrared spectroscopy (FT-IR), and X-ray powder diffraction (XRD). The three spectroscopic methods were compared with respect to their capability of yielding reliable analytical qualitative results. The application of RS yielded less crowded spectra with sharper bands in comparison with those obtained by FT-IR. The analysis of the various mineral layers found in a human stone was possible with RS by focusing the laser beam at the desired layer. Overlapping broad bands were produced from the application of FT-IR, which made it difficult to identify components whose bands showed overlapping. Powder XRD could not be used for accurate analysis of the mineral components of the various stone layers since the material contained in the layers of small stones is not sufficient for analytical purposes. Moreover, the necessary stone grinding precludes the possibility of mineral topological analysis.

THE INHIBITION OF CALCIUM OXALATE MONOHYDRATE CRYSTAL GROWTH BY MALEIC ACID COPOLYMERS

The crystallization of calcium oxalate monohydrate (COM) was investigated at conditions of constant supersaturation both in the absence and in the presence of synthetic maleic acid copolymers at 37C, 0.15 M NaCl. The dependence of the rates of COM crystallization in the absence of inhibitors was found to be second order at low and first order at higher supersaturations suggesting a surface diffusion controlled mechanism. The presence of all copolymers tested at concentration levels up to 5 ppm retarded the rates of COM crystal growth up to 90%. The decrease of the COM crystal growth rates by the polymers depended on the nature of the comonomer polymerized with maleic acid and the order of inhibition was found to be vinyl acetate > N-vinylpyrrolidone > styrene. Taking into consideration kinetics data published in the literature concerning the inhibition of COM crystal growth, it is suggested that molecular weight also plays a role, with more inhibition at higher molecular weights. The morphology of the COM crystals grown was unaffected yet the crystals growing at lower rates in the presence of the copolymers were larger and their size more uniform. It is concluded that maleic acid copolymers are strong inhibitors of the crystallization of COM, the inhibitory activity being more pronounced in the case of the linear copolymers.

Quantitative analysis of impurities in ε-caprolactam by Raman spectroscopy

Laser Raman spectroscopy was used for the quantitative analysis of the most common impurities contained in Iµ-caprolactam: adipic acid, sodium sulfate and ammonium sulfate. Calibration graphs were constructed from spectra obtained from pellets with known quantities of Iµ-caprolactam and each of the impurities. Linear relationships between the caprolactam content and the ratio of the relative intensities at characteristic wavelengths were found for the impurities examined. The calibration lines were defined as: adipic acid–Iµ-caprolactam I915/I746=χ–1cap 0.62 – 0.58; ammonium sulfate–Iµ-caprolactam I975/I746=χ–1cap 2.78 – 2.23; and sodium sulfate–Iµ-caprolactam I994/I746=χ–1cap 4.26 – 4.45. I is the relative Raman intensity at the wavenumber noted by the subscript and χcap is the molar fraction of caprolactam. The detection limits are better than 1 mol% for the impurities examined.

Analysis of Prostatic Stent Encrustation and of Entrapped Urinary Stone Using FT-IR and FT-Raman Spectroscopy

Fourier transform infrared spectroscopy (FT-IR) and Fourier transform Raman spectroscopy (FT-RS) were used in order to characterize the encrusted deposits formed on a metallic thermosensitive prostatic stent. A 4 mm urinary stone entrapped within the lumen was also analyzed. Six different substances, a very rare occurrence, were detected, yielding complex spectra. Struvite (STR), hydroxyapatite (HAP), calcium oxalate monohydrate (COM), potassium urate (PU), and ammonium urate (AU) were the main components of concretion formed on the metal surface. STR and PU were detected on the 0.2 mm external surface of the stone, while the 3.8 mm core was found to be uric acid (UA). The broad and overlapping FT-IR bands of STR and COM made their identification difficult, while the detection of HAP was hindered by the presence of numerous urates bands, which, on the other hand, were used for the discrimination among UA, AU, and PU. Raman spectroscopy proved to be more sensitive to urate presence than did FT-IR, while the identification of STR, COM, and HAP was easier for FT-RS but more difficult with respect to AU and UA since all their bands, but three, coincide. A combination of the two techniques was necessary for the qualitative analysis of the encrustation and the stone.

Influence of operational variables on the crystallization of ε-caprolactam from melts

The effect of operational variables in the process of melt crystallization of e-caprolactam, including water content and cooling rate was investigated. It was found that the metastable range depends linearly on the water content. Higher cooling rates resulted in higher water content of the e-caprolactam crystals grown in water containing melts. In the presence of water, higher cooling rates resulted in the formation of less elongated crystals. In suspensions, the e-caprolactam crystals formed agglomerates. The agglomeration kinetics of crystallites grown from unstirred melts containing 10% w/w water found to fit the perikinetic model.

Nucleation kinetics of ε-caprolactam melts in the presence of water impurity

Abstract The nucleation of e-caprolactam in melts containing water impurities between 3% and 7% w/w was investigated in a batch reactor monitoring melt temperature. The induction times preceding the formation of e-caprolactam nuclei were inversely proportional to the melt supersaturation and a threshold in the supersaturation of about 6% was found for homogenous nucleation. The interfacial tensions calculated using the classical nucleation theory ranged between 0.8 and 1.5 mJ m −2 for water content of 3%–7%, respectively. The concomitant increase of the size of the critical nucleus suggested that water inhibits the process of nucleation of e-caprolactam in melts containing water impurity. This conclusion was further confirmed for the rates of crystal growth of the e-caprolactam in the melts measured from the rates of temperature increase with time.

Encrustation of a Metal Alloy Urinary Stent: A Mechanistic Investigation

Materials and Methods: A section of a metal stent consisting mainly of tantalum coated partially by strongly adhering calcium oxalate monohydrate (COM) crystals was immersed in supersaturated solutions prepared from calcium chloride and sodium oxalate at 37°C and ionic strength 0.15 M in NaCl.AbstractObjectives: To investigate the kinetics of encrustation of a metall alloy urinary stent system in vitro by calcium oxalate and characterize the crystals forming from solutions supersaturated with respect to all calcium oxalate hydrates.Results: The COM–coated stent mineralized upon immersion in the supersaturated solutions. The process was monitored with a calcium ion–selective electrode and the rates were measured at conditions of sustained solution supersaturation. COM crystals formed on the stent and the rate of COM crystal growth yielded a second–order dependence on the solution supersaturation.Conclusions: The deposition of COM crystals on the metal stents coated partially with COM crystals by adhesive forces was found to be most important for the acceleration of the encrustation process. The dependence of the rates on the solution supersaturation suggested absence of secondary nucleation and a surface–controlled process for the encrustation process.