Open-source autosampler for elemental and isotopic analyses of solids

Water temperature affects somatic growth, body condition and oxygen and carbon otolith isotopes of stout whiting (Sillago robusta)

Ocean warming will continue to affect the growth, body condition and geographic distributions of marine fishes and understanding these effects is an urgent challenge for fisheries research and management. Determining how temperature is recorded in fish otolith carbonate, provides an additional chronological tool to investigate thermal histories, preferences and patterns of movement throughout an individual's life history. The influence of three water temperature treatments (22°C, 25°C, and 28°C) on hatchery-reared juvenile stout whiting, Sillago robusta, was tested using a controlled outdoor mesocosm system. Fish were measured for change in length and weight, and body condition was determined using bioelectrical impedance analysis. Sagittal otoliths were analysed for stable oxygen (δ18Ootolith) and carbon (δ13Cotolith) isotopes via isotope ratio mass spectrometry. Whiting kept at 22°C were significantly smaller and had diminished body condition compared to fish in 25°C and 28°C, which did not significantly differ from each other. The δ18O otolith values of stout whiting demonstrated a negative temperature-dependent fractionation relationship which was similar in slope but had a different intercept to the relationships reported for inorganic aragonite and other marine fish species. The δ13C otolith values also showed a negative relationship with water temperature, and the calculated proportion of metabolic carbon M in otoliths differed between fish reared in the coolest (22°C) and warmest (28°C) temperature treatments. Overall, the results suggest that stout whiting may have reached an upper growth threshold between 25°C and 28°C, and that growth and body condition may be optimised during warmer seasons and toward the northerly regions of their distribution. Otolith oxygen thermometry shows promise as a natural tracer of thermal life history, and species-specific fractionation equations should be utilised when possible to prevent errors in temperature reconstructions of wild-caught fish.

Adapting an elemental analyser to perform high-temperature catalytic oxidation for dissolved organic carbon measurements in water

RATIONALE

Many laboratories employ elemental analyzers (EAs) coupled to isotope ratio mass spectrometers (IRMSs) to measure carbon stable isotope ratios (δ¹³ C) in solid samples. Dissolved organic carbon (DOC) in most natural water samples cannot be analyzed using this approach unless time-consuming preconcentration is employed.

METHODS

An EA-IRMS can be used to measure DOC δ¹³ C in natural waters without the need for sample preconcentration by employing high-temperature catalytic oxidation. An autosampler injects water into the EA reactor at 680°C filled with platinum catalyst beads, where all carbon is converted to CO₂ . Remaining water and halides are removed, while CO₂ is trapped in a cryotrap and later released to the IRMS.

RESULTS

Measurements were accurate (deviation <0.3‰ compared to solid sample measurements) and precise (error of 0.3‰ for concentrations ≥46 μM). Blanks were present and accounted for. Salinity up to seawater level did not affect accuracy or precision, but limited the number of samples that could be run before cleaning of the reactor was needed. DOC δ¹³ C in a river/estuary varied between -25.7 and -23.2‰, with higher values for waters with higher salinity, as expected. Deep-sea water reference material had a value of -22.9 ± 0.5‰, very similar to those found in recent reports employing similar techniques.

CONCLUSION

Adapting an EA is a feasible approach for the measurement of DOC δ¹³ C in natural waters. The low cost and simplicity of the system allow its use in any laboratory already equipped with EA-IRMS.

Automated weighing in the stable isotope lab: When less is more

Automated powder weighing is an elusive goal in scientific laboratories. The main problem is that powders are much more heterogeneous than liquids, making difficult the development of a unified automation solution for their handling. A compromise has been presented with miau, a low-cost, open-source autosampler for microbalance. Miau was demonstrably useful to perform the automated weighing of some powders, as long as the same powder is weighed repeatedly, which is useful for preparing standards to be measured along samples. However, in stable-isotope laboratories it is also necessary to weigh samples, which are often very heterogeneous, and thus not amenable for miau. Here it is demonstrated how miau can be adapted to handle not only standards, but also samples, using the "less is more" philosophy:•Miau is simplified to perform only the manipulation of weighing capsules, becoming "miau redux"•Miau redux can be used not only for standards, but for a variety of samples as well•Miau redux saves 64% of operator time when using a microbalance.

Isotopic niche overlap between sympatric Australian snubfin and humpback dolphins

Ecological niche theory predicts the coexistence of closely related species is promoted by resource partitioning in space and time. Australian snubfin (Orcaella heinsohni) and humpback (Sousa sahulensis) dolphins live in sympatry throughout most of their range in northern Australian waters. We compared stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) in their skin to investigate resource partitioning between these ecologically similar species. Skin samples were collected from live Australian snubfin (n = 31) and humpback dolphins (n = 23) along the east coast of Queensland in 2014–2015. Both species had similar δ¹³C and δ¹⁵N values and high (>50%) isotopic niche space overlap, suggesting that they feed at similar trophic levels, have substantial dietary overlap, and rely on similar basal food resources. Despite similarities, snubfin dolphins were more likely to have a larger δ¹⁵N value than humpback dolphins, indicating they may forage on a wider diversity of prey. Humpback dolphins were more likely to have a larger δ¹³C range suggesting they may forage on a wider range of habitats. Overall, results suggest that subtle differences in habitat use and prey selection are likely the principal resource partitioning mechanisms enabling the coexistence of Australian snubfin and humpback dolphins.

Miau, a microbalance autosampler

Powder weighing is an essential but tedious activity in many branches of science. Here I describe a MIcrobalance AUtosampler (miau) that transfers solids in the sub-mg range to a microbalance. Miau is a pick-and-place machine which moves a gripper with dual function: 1) move tin capsules; 2) deliver powder from a container to tin capsules. In our laboratory we routinely use miau to prepare working standards for quality control of elemental and isotopic analyses. In a test, miau produced standards between 0.3 and 1.1 mg, which is a useful range in our laboratory. Failure to produce a weighed standard happened in 5% of the cases. A comparison with manual measurements demonstrated that obtained amounts for automated samples were as accurate and precise as manually prepared ones. Setup for daily use is simple, and the microbalance can be easily used alternately with or without miau. Miau is a low-cost device that can work with microbalances from many manufacturers, and can be readily adopted by many laboratories.

Comparison of Design Approaches for Low-Cost Sampling Mechanisms in Open-Source Chemical Instrumentation

Robotic positioning systems are used in a variety of chemical instruments, primarily for liquid handling purposes, such as autosamplers from vials or well plates. Here, two approaches to the design of open-source autosampler positioning systems for use with 96-well plates are described and compared. The first system, a 3-axis design similar to many low-cost 3D printers that are available on the market, is constructed using an aluminum design and stepper motors. The other system relies upon a series of 3D printed parts to achieve movement with a series of linker arms based on Selective Compliance Assembly Robot Arm (SCARA) design principles. Full printer design files, assembly instructions, software, and user directions are included for both samplers. The positioning precision of the 3-axis system is better than the SCARA mechanism due to finer motor control, albeit with a slightly higher cost of materials. Based on the improved precision of this approach, the 3-axis autosampler system was used to demonstrate the generation of a segmented flow droplet stream from adjacent wells within a 96-well plate.

Low-cost and open-source strategies for chemical separations

In recent years, a trend toward utilizing open access resources for laboratory research has begun. Open-source design strategies for scientific hardware rely upon the use of widely available parts, especially those that can be directly printed using additive manufacturing techniques and electronic components that can be connected to low-cost microcontrollers. Open-source software eliminates the need for expensive commercial licenses and provides the opportunity to design programs for specific needs. In this review, the impact of the "open-source movement" within the field of chemical separations is described, primarily through a comprehensive look at research in this area over the past five years. Topics that are covered include general laboratory equipment, sample preparation techniques, separations-based analysis, detection strategies, electronic system control, and software for data processing. Remaining hurdles and possible opportunities for further adoption of open-source approaches in the context of these separations-related topics are also discussed.

Portable open-source autosampler for shallow waters

Automated water sampling can be very useful, but open-source choices are limited. Here I present an autosampler which consists of a gantry robot that delivers water from a syringe pump to 24 capped 40 ml vials. The autosampler is controlled using an Android tablet automatized using Macrodroid. Three rinsing cycles ensure negligible carryover between consecutive samples. Hourly sampling from a creek under rainy conditions suggested that total organic carbon in water was diluted by the rain. Some important limitations: 1) the autosampler must be on a steady, flat, horizontal surface; 2) unattended sampling can only last as long as the batteries powering the tablet and the motors; 3) distance from the syringe pump to water cannot exceed ~2 m in height and ~4 m in length for 3 mm tubing; 4) sampling frequency does not exceed one sample every eleven minutes. However, because of its open design, the autosampler can be modified and improved to not only overcome these limitations, but also potentially expand its scope to more demanding sampling if necessary.