Radiocarbon dioxide detection using cantilever-enhanced photoacoustic spectroscopy.

In this Letter, we report on the sub-parts-per-billion-level radiocarbon dioxide detection using cantilever-enhanced photoacoustic spectroscopy. The 14C/C ratio of samples is measured by targeting a 14CO2 absorption line with minimal interference from other CO2 isotopes. Using a quantum cascade laser as a light source allows for a compact experimental setup. In addition, measurements of sample gases with 14CO2 concentrations as low as 100 parts-per-trillion (ppt) are presented. The Allan deviation demonstrates a noise equivalent concentration of 30 ppt at an averaging time of 9 min. The achieved sensitivity validates this method as a suitable alternative to more complex optical detection methods for radiocarbon dioxide detection used so far, and it can be envisioned for future in situ radiocarbon detection.

Broadband Laser-Based Infrared Detector for Gas Chromatography.

Cantilever-enhanced photoacoustic spectroscopy coupled with gas chromatography is used to quantitatively analyze a mixture of alcohols in a quasi-online manner. A full identification and quantification of all analytes are achieved based on their spectral fingerprints using a widely tunable continuous-wave laser as a light source. This can be done even in the case of interfering column/septum bleed or simultaneously eluted peaks. The combination of photoacoustic spectroscopy and gas chromatography offers a viable solution for compact and portable instruments in applications that require straightforward analyses with no consumables.

Broadband photoacoustic spectroscopy of CH414 with a high-power mid-infrared optical frequency comb.

We report a photoacoustic spectroscopy setup with a high-power mid-infrared frequency comb as the light source. The setup is used in broadband spectroscopy of radiocarbon methane. Owing to the high sensitivity of a cantilever-enhanced photoacoustic cell and the high-power light source, we can reach a detection limit below 100 ppb in a broadband measurement with a sample volume of only a few milliliters. The first infrared spectrum of CH414 is reported and given a preliminary assignment. The results lay a foundation for the development of optical detection systems for radiocarbon methane.

Cavity-enhanced cantilever-enhanced photo-acoustic spectroscopy.

We have improved the sensitivity of a state-of-the-art cantilever-enhanced photo-acoustic trace gas sensor by combining it with an optical power build-up cavity. The build-up cavity enhances the photo-acoustic signal by a factor of ∼100, resulting in an exceptionally good normalised noise equivalent absorption (NNEA) value of 1.75 × 10-12 W cm-1 Hz-1/2. We demonstrate the sensor platform in the 1530 nm wavelength range with a simple distributed feedback diode laser, achieving 75 ppt sensitivity for C2H2 with a 10 s integration time.

Spectroscopic thermometry for long-distance surveying.

Electronic distance meters are routinely used to accurately determine the distance between two points. To reach relative measurement uncertainties of 10-7, the average temperature along the beam has to be known within 100 mK since it is a key component in determining the refractive index of air. Temperature measurements at this level are extremely challenging over long distances and especially in an outdoor environment. This paper presents a thermometer for accurate temperature measurements over distances up to a few km. The thermometer is based on direct laser absorption spectroscopy of oxygen near 770 nm. The thermometer yields a spatially continuous measurement of air temperature, and it can provide spatially and temporally well-matching data with an actual distance-measuring laser beam. A field measurement campaign at the 864-m Nummela standard baseline demonstrates applicability of the developed thermometer for improving the refractive index compensation of current high-performance electronic distance meters.

Rheological insights into 3D printing of drug products: Drug nanocrystal-poloxamer gels for semisolid extrusion.

The importance of ink rheology to the outcome of 3D printing is well recognized. However, rheological properties of printing inks containing drug nanocrystals have not been widely investigated. Therefore, the objective of this study was to establish a correlation between the composition of nanocrystal printing ink, the ink rheology, and the entire printing process. Indomethacin was used as a model poorly soluble drug to produce nanosuspensions with improved solubility properties through particle size reduction. The nanosuspensions were further developed into semisolid extrusion 3D printing inks with varying nanocrystal and poloxamer 407 concentrations. Nanocrystals were found to affect the rheological properties of the printing inks both by being less self-supporting and having higher yielding resistances. During printing, nozzle blockages occurred. Nevertheless, all inks were found to be printable. Finally, the rheological properties of the inks were successfully correlated with various printing and product properties. Overall, these experiments shed new light on the rheological properties of printing inks containing nanocrystals.

Use of dairy industry side-stream lactose for tablet manufacturing - proof of concept study.

During recent years there have been shortages of certain drugs due to problems in raw material supply. These are often related to active ingredients but could also affect excipients. Lactose is one of the most used excipients in tableting and comes in two anomeric and several solid-state forms. The aim of this study was to utilize lactose from a dairy side-stream and compare it against a commercial reference in direct compression. This would be a sustainable option and would secure domestic availability during crises. Two types of lactose, spray-dried and freeze-dried, were evaluated. Lactose was mixed with microcrystalline cellulose in different ratios together with lubricant and glidant, and flowability and tabletability of the formulations was characterized. The fully amorphous and small particle-sized spray-dried lactose flowed inadequately but exhibited good tabletability. The larger particle-sized, freeze-dried lactose exhibited sufficient flow and better tabletability than the commercial reference. However, disintegration and drug release were slower when using the investigational lactose formulations. This was most likely due to remaining milk proteins, especially caseins, in the lactose. Overall, the investigational lactose provides promise for the use of such a side-stream product during crisis situations but enhancing their properties and/or purity would be needed.

Sub-parts-per-trillion level sensitivity in trace gas detection by cantilever-enhanced photo-acoustic spectroscopy.

An exceptional property of photo-acoustic spectroscopy is the zero-background in wavelength modulation configuration while the signal varies linearly as a function of absorbed laser power. Here, we make use of this property by combining a highly sensitive cantilever-enhanced photo-acoustic detector, a particularly stable high-power narrow-linewidth mid-infrared continuous-wave optical parametric oscillator, and a strong absorption cross-section of hydrogen fluoride to demonstrate the ability of cantilever-enhanced photo-acoustic spectroscopy to reach sub-parts-per-trillion level sensitivity in trace gas detection. The high stability of the experimental setup allows long averaging times. A noise equivalent concentration of 650 parts-per-quadrillion is reached in 32 minutes.