Jimmy Bak

FTIR emission spectroscopy methods and procedures for real time quantitative gas analysis in industrial environments

Diagnostic tools for real time and direct gas analysis have been developed. The simultaneous measurements of gas and particle temperatures (280-330 °C) and gas concentrations (CO, CO2, HCl, H2O) are demonstrated in a hot particle-laden flue gas with a fibre-optic probe connected to a Fourier transform infrared spectrometer. The gas temperature is found from the thermal radiation at the 2350 cm-1 CO2 fundamental band, whereas the gas concentrations are determined by comparing the measured transmittance spectra with a spectroscopic database and validation measurements using the Hotgas facility at Riso. Measurement uncertainties are discussed. The measured local gas temperatures and concentrations are in good agreement with measurements made with conventional equipment.

Influence of temperature on water and aqueous glucose absorption spectra in the near- and mid-infrared regions at physiologically relevant temperatures

Near- and mid-infrared absorption spectra of pure water and aqueous 1.0 g/dL glucose solutions in the wavenumber range 8000–950 cm−1 were measured in the temperature range 30–42 °C in steps of 2 °C. Measurements were carried out with an FT-IR spectrometer and a variable pathlength transmission cell controlled within 0.02 °C. Pathlengths of 50 μm and 0.4 mm were used in the mid- and near-infrared spectral region, respectively. Difference spectra were used to determine the effect of temperature on the water spectra quantitatively. These spectra were obtained by subtracting the 37 °C water spectrum from the spectra measured at other temperatures. The difference spectra reveal that the effect of temperature is highest in the vicinity of the strong absorption bands, with a number of isosbestic points with no temperature dependence and relatively flat plateaus in between. On the basis of these spectra, prospects for and limitations on data analysis for infrared diagnostic methods are discussed. As an example, the absorptive properties of glucose were studied in the same temperature range in order to determine the effect of temperature on the spectral shape of glucose. The change in water absorption associated with the addition of glucose has also been studied. An estimate of these effects is given and is related to the expected level of infrared signals from glucose in humans.

Determination of urea, glucose, and phosphate in dialysate with Fourier transform infrared spectroscopy

Individual control and quantification of phosphate removal is desirable in dialysis treatment. Currently, no on-line method exists to quantify phosphate removal. We demonstrate that a multivariate calibration model based on infrared transmission spectra is capable of predicting phosphate, urea, and glucose concentrations at clinically relevant levels. The on-line monitoring of these components by infrared spectroscopy is therefore feasible.

Quantitative Gas Analysis with FT-IR: A Method for CO Calibration Using Partial Least-Squares with Linearized Data

Calibration spectra of CO in the 2.38–5100 ppm concentration range (22 spectra) have been measured with a spectral resolution of 4 cm−1, in the mid-IR (2186–2001 cm−1) region, with a Fourier transform infrared (FT-IR) instrument. The multivariate calibration method partial least-squares (PLS1) was used to model the CO calibration spectra in order to improve the sensitivity and to flag possible outliers in the prediction step. The relation between the absorbance values and concentrations was strongly nonlinear. This result was caused mainly by the low spectral resolution of the instrument. To improve the model predictions, we have linearized the data prior to making the model calculations. The linearization scheme presented here simplified the data pretreatment, because the function needed to linearize the data might be approximated by co-absorbance peak areas representing the concentrations. The integrated absorbance areas, rather than the concentration values, were used as input to the PLS algorithm. A fifth-order polynomial was used to calculate the concentrations from the predicted absorbance areas. The PLS algorithm used on the linearized data reduced the number of factors in the calibration model. Our results reveal that the calibration model based on the linearized data had a high concentration prediction accuracy throughout the entire concentration range.

Disinfection of Pseudomonas aeruginosa biofilm contaminated tube lumens with ultraviolet C light emitting diodes

Bacterial biofilms on long-term catheters are a major source of infection. Exposure to ultraviolet C (UVC – 265 nm) light was shown in an earlier study to reduce the number of bacteria substantially on ex vivo treated urinary patient catheters. Very large doses (long treatment times) should, however, be applied to obtain 99.9% disinfection rates. The major reason was that besides cells the mature biofilm contained absorbing and scattering particulates, which made the biofilm opaque. The potential of UVC light emitting diodes (LED) for disinfection purposes in catheter-like tubes contaminated with biofilm was investigated. It was shown that UVC light propagation was possible through both Teflon and catheter tubes (silicone). The disinfection efficiency of the diodes was demonstrated on tubes contaminated artificially with a Pseudomonas aeruginosa biofilm. The tubes were connected to a flow system and biofilms were produced during a 3 day period. Tubes in lengths of 10 (Teflon, silicone) and 20 cm (Teflon) were contaminated. Tubes for control and for UVC treatment were contaminated in parallel. Biofilms were sampled from the total inner surface of the tubes. Colony counts on the control samples were in the range of 5 × 105–1.3 × 109 CFU ml−1, with disinfection rates in the range 96–100%. The applied UVC doses corresponded to treatment times between 15 and 300 min. Disinfection (100%) was obtained in 10 cm Teflon tubes exposed for 30 min (detection limit <5 CFU ml−1). The same result was obtained for a 20 cm Teflon tube exposed for 300 min. The disinfection rate was 96% for the 20 cm tube if the dose was reduced to 30 min. A disinfection rate of 99.99% was observed for a 10 cm peritoneal dialysis catheter tube (silicone) exposed for 300 min. Differences between the tubes were dependent on the differences in length and the type of the material. The UVC light was transmitted six times more efficiently in Teflon than in silicone tubes of equal length (10 cm). The germicidal effect to obtain a 99.99% killing rate for the biofilm (∼78 J m−2) is comparable to that for the planktonic bacterium. It is concluded that there is potential for LED UVC light sources if they are used for disinfection of thin biofilms.

Near-Infrared Transmission Spectroscopy of Aqueous Solutions: Influence of Optical Pathlength on Signal-to-Noise Ratio

The optimal choice of optical pathlength, source intensity, and detector for near-infrared transmission measurements of trace components in aqueous solutions depends on the strong absorption of water. In this study we examine under which experimental circumstances one may increase the pathlength to obtain a measurement with higher signal-to-noise ratio. The noise level of measurements at eight different pathlengths from 0.2 to 2.0 mm of pure water and of 1 g/dL aqueous glucose signals were measured using a Fourier transform near-infrared spectrometer and a variable pathlength transmission cell. The measurements demonstrate that the noise level is determined by the water transmittance. The noise levels in the spectral region from 5000 to 4000 cm−1 show that the optimal pathlength (0.4 mm) is the same for pure water and 1 g/dL aqueous glucose solutions. When detector saturation occurs it is favorable to increase the pathlength instead of attenuating the light source. The obtained results are explained by an analytical model.

Dose requirements for UVC disinfection of catheter biofilms

Bacterial biofilms on permanent catheters are the major sources of infection. Exposure to ultraviolet-C (UVC) light has been proposed as a method for disinfecting the inner surface of catheters. Specification of a UVC-based device for in vivo disinfection is based on the knowledge of the required doses to kill catheter biofilm. Given these doses and the power of available UVC light sources, calculation of the necessary treatment times is then possible. To determine the required doses, contaminated urinary catheters were used as test samples and UVC treated in vitro. Patient catheters (n = 67) were collected and cut into segments of equal size and treated with various UVC doses. After treatment, the biofilm was removed by scraping and quantified by counting colony forming units. Percentage killing rates were determined by calculating ratios between UVC-treated samples and controls (no UVC treatment). Mean killing rates were 89.6% (0.5 min), 98% (2 min), and 99% (60 min). Approximately 99% killing was obtained with a UVC dose of 15 kJ m−2. This dose, which is about 100 to 1000 times greater than the lethal dose for planktonic cells, is expected to be the maximum dose required to maintain newly inserted catheters free of contamination. The combination of high doses required to kill mature biofilm and the limited effect of current UVC light sources result in a relative long treatment time (∼60 min). If a UVC-based method is to be of practical use for disinfection of catheters in the clinic, repeated preventive treatments should be carried out on newly inserted catheters.

Degradability of aged aquatic suspensions of C60 nanoparticles

In this study, aged aqueous suspensions of C(60) (nC(60)) were investigated in the respirometric OECD test for ready biodegradability. Two suspensions of nC(60) were prepared by stirring and aged under indirect exposure to sunlight for 36 months. ATR-FTIR analyses confirmed the presence of C(60)-structures in the suspensions. Samples of the nC(60) suspensions (20mg/l) were inoculated with activated sludge (30 mgTSS/L) and incubated in a mineral medium under aerobic conditions. Since no mineralisation of nC(60) was observed after 28 days of incubation, 5mg/l sodium acetate was added to the media. After additional 20 days, no mineralisation of nC(60) was observed. However, within a few days sodium acetate was completely mineralised, showing that the biomass was not inhibited by the presence of nC(60). Based on results from this simple approach, aged nC(60) can be classified as not ready biodegradable according to the standard OECD test procedure.

Online monitoring of urea concentration in dialysate with dual-beam Fourier-transform near-infrared spectroscopy

The robustness of a dual-beam, optical null, Fourier-transform near-infrared (FTNIR) spectrometer was investigated by means of online, near-infrared measurements and predictions of urea concentrations in spent dialysate during hemodialysis treatment. Simple multivariate calibration using a few factors based on a small number of prepared samples provided stable and accurate predictions over a period of 1 month. The calibration was robust when faced with adjustment of reference cell intensity and did not require a daily measured reference spectrum. The root-mean-square error of prediction of urea was 0.4 mM based on a two-factor partial least-squares regression model.

A hot gas facility for high-temperature spectrometry

A hot gas facility is described for determining molecular absorption data and validating spectroscopically based gas analyser systems. The facility comprises a newly developed heated 0.50 m stainless steel gas flow cell mounted with CaF2 windows, which can be operated from ambient to 1100 K. The heated cell is interfaced to a Fourier transform infrared spectrometer and a black body source, and is characterized by a uniform temperature profile over the entire path length. This profile is demonstrated by measuring the gas temperature of carbon dioxide using spectroscopic methods based on transmission-emission spectra measured simultaneously and comparing the results of these measurements with those using thermocouples. It is found that the temperatures determined by spectroscopic methods are within the uncertainty of those measured by thermocouples (±2.9 K at 1072.0 K and ±0.7 K at 462.9 K). The gas enclosed in the cell is therefore to be considered as a uniform slab of gas. In addition, the shape of the measured emission spectra, which are very sensitive to self-absorption effects caused by small amounts of cold gas molecules present in the light path, are shown to be equal to those of the transmittance spectra to within 1% (~1-2 K). This indicates that the presence of cold gas molecules close to the windows and in the light path is negligible.