Unstable Temperature Research Articles

Envelope Deficiencies and Thermo-Hygrometric Challenges in Warehouse-Type Buildings in Subtropical Climates: A Case Study of a Nori Distribution Center

Enhancing the energy efficiency and climate resilience of existing buildings is crucial amid growing environmental challenges. While extensive research has focused on non-residential buildings, studies on thermo-hygrometric conditions in warehouse-type buildings, particularly in subtropical climates, remain limited. This study investigated the impact of building envelope deficiencies on indoor thermal and moisture regulation at the Nori Distribution Center. Using infrared thermal imaging and long-term environmental monitoring, significant thermo-hygrometric fluctuations were identified, primarily due to design and construction deficiencies. Poor insulation, inadequate sealing, and the lack of moisture barriers contributed to unstable indoor temperature and humidity. Seasonal analysis showed that during summer, the median second-floor air temperature reached 28.8 °C, peaking at 39.2 °C, with relative humidity exceeding 70% for 45% of the time. First-floor relative humidity surpassed 70% for 72% of the time. While condensation risk remains low year-round, it increases significantly with air infiltration through gaps in the building envelope. This study recommends enhancing the sealing of the building envelope, upgrading insulation materials and moisture barriers, particularly in the roof, and optimizing the HVAC system to improve energy efficiency and storage conditions. These findings offer valuable recommendations for retrofitting warehouse-type buildings in subtropical climates to improve energy efficiency and climate resilience.

Growing Tomato Seedlings Suitable for Mechanical Grafting under Regulated Light Regime

Abstract: The uniformity of growth and mechanical properties of grafted seedlings affect the quality of mechanical grafting operations. The growth uniformity of grafted seedlings in a greenhouse will be poor due to the uneven and unstable light and temperature conditions. Plant factories can cultivate grafted seedlings in the most suitable environment by regulating environmental parameters such as light and temperature. The aim of this study was to investigate the impact of the light conditions on tomato seedlings in plant factory and to develop an optimal cultivation light formula. The effects of light intensity (50, 100, 150, 200, and 250 μmol m−2 s−2) and photoperiod (10, 12, 14, 16, and 18 h a day(h/d)) on the morphological and mechanical properties of tomato seedlings were experimentally investigated. Orthogonal experiments were conducted involving light quality (R:B = 75:25, R:B = 50:50, and R:B = 25:75), light intensity (150 μmol m−2 s−2, 200 μmol m−2 s−2, and 250 μmol m−2 s−2), and photoperiod (14, 16, and 18 h/d) as independent variables to determine the optimal combination. Finally, a comparative grafting experiment was conducted between the seedlings cultivated using the optimal light formula and commercially available seedlings. The result showed that increasing light intensity inhibited hypocotyl length and promoted seedling stem growth, and excessive light intensity decreased seedling mechanical properties. The optimal light intensity for rootstocks is 200 μmol m−2 s−2, and the optimal light intensity for scions is 250 μmol m−2 s−2. Shortening the photoperiod would promote hypocotyl growth and inhibit seedling stem elongation. Different photoperiods had a significant impact on the mechanical properties of tomato seedlings. The most suitable photoperiod for rootstocks was 18 h/d and for scions was 16 h/d. The most suitable light formula was R:B = 50:50, 250 μmol m−2 s−2, 18 h/d. By analyzing the experimental results, the mechanical properties of seedlings grown by the regulated light environment were better than those of commercially available seedlings, and the success rate of mechanical grafting was 7% higher. Overall, in plant factories compared to commercially available tomato seedlings, tomato seedlings cultivated by the regulated light environment were more suitable for mechanical grafting. This research result provides theoretical support for subsequent research on grafting machinery.

Numerical simulation and experimental verification of dynamic cooling and temperature control of the optical cavity in a CO2 isotope analyzer

Accurate measurement of CO2 generated from different emission sources is the basis for controlling CO2 emissions and mitigating global warming. With advantages of high accuracy and rapid response, isotope analyzers using spectroscopic techniques, particularly those using cavity ring-down spectroscopy, have been widely used for CO2 emissions monitoring. However, these analyzers often face challenges such as spectral interference from impurity gases and unstable temperature control within the optical cavity in isotope analyzers. To address these challenges, this paper proposes a low-temperature optical cavity scheme utilizing a split Stirling-type pulse tube cryocooler. Combining thermal boundary conditions with particle swarm optimization, a dynamic cooling and temperature control model of the optical cavity was established in MATLAB. The model subsequently analyzed the cooling process, temperature control, and stability of the optical cavity. After 120 h, the simulations showed that the central part of the optical cavity had cooled to 126.4 K with a heat leakage of 8.90 W, in agreement with the experimental results that stabilized at 126.8 K. The temperature fluctuations remained within 0.1 K/h while controlling an overall temperature of 170 K with a temperature difference of ± 5 K. Changes in the electrical input power of cryocooler had no influence on the temperature distribution. This advancement not only lowers the operating temperature of the optical cavity to minimize spectral interference but also enhances the precision and efficiency of temperature control.

Influences of thermal and mass stratification on unsteady magnetohydrodynamics parabolic flow along an infinite vertical plate with periodic temperature variation and exponential mass diffusion in porous medium

AbstractThis study explores the dynamics of unsteady magnetohydrodynamics (MHD) parabolic flow along an infinite vertical plate, emphasizing the effects of thermal and mass stratification in a porous medium subjected to periodic temperature variation and exponential mass diffusion. Utilizing the Laplace transform technique to obtain precise solutions, this study effectively integrates the impacts of both thermal and mass stratification without dependence on approximations. The main goal is to assess how thermal and mass stratification impact MHD flow dynamics, temperature, and concentration profiles under varying conditions. The study provides a thorough comparison of these findings with traditional nonstratified scenarios, presenting a comprehensive analysis of fluid behavior under diverse conditions. The conclusions reveal that thermal and mass stratifications considerably diminish velocity and stabilize temperature distributions, which suggests a damping influence on fluid movement and improved management of diffusion processes. Enhanced Grashof numbers improve heat and mass transfer efficiency, while magnetic and Darcy parameters significantly influence flow resistance and heat transfer characteristics. These conditions also result in higher Nusselt and Sherwood numbers, indicating increased efficiency in heat and mass transfer. In contrast, scenarios without stratification display higher velocities and more unstable temperature and concentration profiles. The findings highlight the critical role of stratification in improving fluid dynamics and increasing the efficiency of heat and mass transfer processes, offering valuable insights for engineering and environmental applications in similar conditions. The main novelty of the research is being the first to use the Laplace transform for exact solutions on combined thermal and mass stratification in MHD flows, enhancing prediction accuracy and process control.

High Single-Event Burnout Resistance 1.2 kV 4H-SiC Schottky Barrier Diode

A 1.2 kV lateral RESURF Schottky diode (TZ-SBD) have been designed from SZ-SBD that can recover from a single-event effect (SEE) in which a heavy ion traverses the device at a linear energy transfer (LET) of 60 MeV·cm²/mg, ESA’s standard. Compared to SZ-SBD, TZ-SBD has an additional split in the N-drift region which is usually used to improve the electric field distribution so its breakdown voltage is improved by 9%. During the single events simulations, the maximum temperature is 919 K with reverse voltage (VR) = 1200 V and LET = 60 MeV·cm²/mg, which is much lower then the SiC melting temperature (3100 K) and the chemically unstable temperature of SiC in the presence of metal (1073 K).

High-efficiency adaptive temperature control for thermoelectric system based on the OBPPID strategy

Thermoelectric cooler (TEC) is widely used for temperature control in optoelectronics, machinery, biomedicine, and other fields. However, the unstable temperature control over wide ranges and different gradients restricts the efficiency of TEC. To highlight the neural network’s effectiveness in controlling TEC systems, the optimized BPPID (OBPPID) strategy is proposed. In the OBPPID strategy, the factors s̃ and G are decided through formula derivation and the particle swarm optimization (PSO) algorithm, respectively contributing to the backward adjustment and forward propagation of BPPID. The OBPPID solves three issues that the BPPID faces: gradient vanishing of network weights, over-reliance of initial network weights and range constraint of control parameters. The OBPPID and BPPID have been simulated 1000 times to evaluate control performance. The results show that, with random initial network weights, the OBPPID strategy reduces the cost variability of the BPPID strategy from 92 to 17, achieving an 81.52% reduction. Physical tests have confirmed that in the temperature control over wide range and the temperature gradients of 5°C, 20°C, and 80°C, the OBPPID strategy can adaptively adjust the control parameters and provide higher efficiency than PID, BPPID and fuzzy PID strategies for TEC system.

Positional Regulation, Sucking Reflex and Incidence When Given Nutrition Through OGT in High-Risk Infants with Low Birth Weight Infants in the Nicu Room: A Case Study of Waled Hospital

High-risk babies are babies born at 32 – 36 weeks of gestation/prematurely, babies whose mothers suffer from Diabetes Mellitus, babies with a history of apnea, babies with seizures, sepsis, asphyxia, babies with bleeding disorders or breathing problems. Problems that often arise in cases of LBW babies include unstable body temperature, breathing problems, digestive and nutritional disorders, liver immaturity, anaemia, intraventricular bleeding, seizures, infections, hypoglycemia, hyperglycemia and hypocalcemia. This study aims to provide nursing care to babies at high risk in the Nicu Room at Waled Hospital, Cirebon Regency, on 27 December 2023. Examination of the sucking reflex is recommended as a screening that shows intact motor neuron function in neonates. The sucking reflex is well-developed in normal babies and is coordinated with breathing. Inhibition of the sucking reflex in the first hours of life will affect the ability to suck at the beginning of life and will directly hinder the nutritional intake received by the baby. Arranging sleeping positions for newborn babies is the role of the neonatal nurse in providing routine daily care. Positioning, especially for premature babies, is not easy. Positioning errors can result in changes in physiological status (increased respiratory rate, pulse frequency, and decreased oxygen saturation), disturbed comfort and quality of sleep, drinking intolerance, hip joint deformity, and bleeding in the brain. The issues affecting all three clients have not been resolved. However, interventions such as positioning, assessing sucking reflexes in high-risk babies, and providing nutrition through OGT are ongoing, with efforts to set the supine sleep position during enteral nutrition. While the problems faced by the high-risk infants in this study are not yet resolved, ongoing nursing interventions are crucial in managing their care. Continued attention to proper positioning, monitoring of sucking reflexes, and nutritional support through OGT is vital for improving the health outcomes of these vulnerable infants.

Development of Smart Hydroponics System using AI-based Sensing

This paper proposes a smart hydroponic system that operates automatically using a fuzzy logic algorithm, integrating IoT functionalities to support smart agriculture. The system allows for remote monitoring and control via the internet, providing real-time data on water levels, pH levels, temperature, and nutrient solution temperature. Precise dosing and temperature control are critical for optimal plant growth, and the system schedules temperature measurements to ensure stability. Unstable temperature can affect pH levels, thereby impacting nutrient absorption. The proposed system employs sensors to continuously monitor the electrical conductivity (EC) and pH levels of the nutrient solution. Fuzzy control is utilized to regulate the nutrient solution pump, automatically adjusting EC and pH levels to promote optimal plant growth. This approach reduces the time burden on producers and provides more precise control over the nutrient solution, resulting in improved growth outcomes. The main contributions of this work are as follows: the development and implementation of an AI-based system integrating a controller, IoT environment, fuzzy logic algorithm, and NFT (nutrient film technology) hydroponics; the creation of a user-friendly interface for farmers through the Smart-Hydroponic application, enabling hybrid monitoring and control of hydroponic farms; the establishment of an IoT-based cloud environment for sensor data monitoring; the implementation of a smart hydroponic system for nutrient sensing, monitoring, and control; and a comparative analysis between smart and conventional hydroponics based on morphological results.

Физиологическое состояние стерляди в условиях садковых и бассейновых хозяйств

The growing conditions of sturgeon fish affect the growth and physiological state, their morphological characteristics. The study of changes in physiological processes under the influence of a complex of factors in the conditions of cage complexes and closed water supply systems will allow for timely adjustment of technology and reduce risks when growing commercial products. The repair and breeding herds of fish breeding enterprises contain sterlet individuals of different ages, which annually, upon reaching puberty, enter the fish breeding process as producers. In this regard, we have studied the main morphophysiological indicators of two-year-olds kept in cages and in closed water supply installations (CWSI). The influence of environmental factors was noted not only on growth indicators, but also on the size of the internal organs of fish and their condition. The unstable temperature regime in the cages, dependence on unpredictable changes in the hydrochemical parameters of the aquatic environment contributes to deep physiological transformations of an adaptive nature, which slows down the growth rate and accumulation of reserve substances. Changes in morphometric parameters were also evident. In sturgeon, there is an increase in the relative weight of the heart, spleen and gonads, a decrease in the weight of the kidneys and liver. The influence of optimal temperature and trophic conditions on the index of the gastrointestinal tract was noted, which was slightly lower in fish from the CWSI than in individuals exposed to negative factors in cages. Sterlet blood counts, regardless of the conditions of detention, corresponded to physiologically healthy individuals. The creation of optimal hydrological and trophic conditions in CWSI contribute to the accumulation of phospholipids and linolenic fatty acids in tissues, which play an important role in the adaptation of the body to negative environmental factors.

Temperature Effect on the Interlayer Exchange Interaction in a Co/Pd/Co Heterostructure

Using Kerr microscopy, the magnetization reversal of the Co(0.4 nm)/Pd(6 nm)/Co(0.4 nm) heterostructure was studied in the temperature range 15–300 K. The temperature dependence of the domain nucleation field in a sample magnetized to saturation was obtained. The nucleation field in both ferromagnetic layers was shown to decrease monotonically with increasing temperature. A region of unstable temperatures of 160–174 K was found, below which the through domains of the new phase nucleated simultaneously in both layers, while in this region domains also nucleated simultaneously in different layers, but in different sites of the sample. The temperature dependence of the effective field HJ of the interlayer exchange interaction was obtained, which increased or decreased the pressure on the domain wall depending on whether this field was added to or subtracted from the external field.

Thermally compensated common-path differential interferometer with reduced long-term zero-drifts

Abstract Laser interferometers have served as the workhorses in the metrology of length for several decades. Their broader application brings further challenges, especially for longer measurement time-frames or outside the laboratory environment with strictly controlled conditions. As a part of our team’s activities aiming at characterizing and eliminating the effects of unstable temperature on interferometric length measurements, we report on successfully remodelling a differential interferometer’s optical arrangement focused on increasing resilience against temperature changes. The experimental characterization under constant temperature and subsequently under thermal load proved a tenfold decrease in short-term fluctuations and reduced sensitivity to temperature changes by a factor of 100.

A measurement method for zero-degree thermostat

Thermocouple thermometers are widely used in laboratories and industry, the ice-water mixture is usually used as cold end compensation for thermocouple thermometer measurement. However, the ice-water mixture has disadvantages, such as complex manufacturing process, short use time, and unstable internal temperature field. The zero-temperature thermostat can replace the traditional ice water mixture to provide a stable temperature field environment. However, there is no suitable measurement method that can evaluate the zero-degree thermostat to meet the measurement requirements of thermocouple thermometer. Therefore, comparative experiments on temperature deviation, volatility, axial temperature field uniformity, radial temperature field uniformity, and load characteristics of the ice-water mixture and the zero-temperature thermostat are evaluated. In addition, the uncertainty of the zero-temperature thermostat and the ice water mixture is also proposed. The results reveal that the measurement results of temperature deviation, volatility, axial temperature field uniformity and load characteristic of the zero-temperature thermostat is smaller than that of the ice water mixture. Meanwhile, the uncertainty results also reveal that the zero-temperature thermostat is more stable than the ice water mixture. This study provides a comprehensive method for evaluating the performance of zero temperature thermostats, which can be used to verify the accuracy of the instrument and ensures the reliability of the thermocouple thermometers measurement, and promotes the development of zero temperature thermostat in temperature measurement field.

Real-time Fishpond Water Temperature Monitoring with Internet of Things (IoT) Technology

The quality of pond water is an important factor in ensuring the health and sustainability of the organisms within it. Internet of Things (IoT) technology has enabled the development of sophisticated and effective monitoring systems to monitor water quality in real-time. One important parameter that needs to be monitored is the temperature of the pond water, as unstable temperatures can harm aquatic organisms. To obtain good quality and disease-free fish at normal times, the optimal temperature for catfish fry is around 28˚C - 30˚C. Manual monitoring or using thermometer measuring instruments is still very traditional and limited to the ability of supervisors to carry out continuous monitoring and may cause delays in detecting significant temperature changes. This research aims to analyze the monitoring system of pool water quality based on temperature by utilizing IoT technology. The proposed system uses a DS18B20 temperature sensor that is wirelessly connected to the IoT network. The temperature data collected in real time will be uploaded to Firebase for storage and further analysis. Through the development of this IoT-based pond water quality monitoring system, it is expected to increase efficiency and reliability in monitoring pond water quality. From the monitoring conducted for approximately 24 hours, the temperature in the fishpond is 28°-30°. After analyzing with direct monitoring, the good temperature is at night at 18.00-00.00 WIB. In conjunction with a standard thermometer, resulted in an average temperature sensor error rate of less than 5%, highlighting the reliability of the IoT technology in real-time environmental monitoring.

Rancang Bangun Alat Pengasap Tipe Paralel

This research aims to design, manufacture and test a parallel type smoker which has an output that can be controlled and has uniform temperature in each smoker cabinet. In this research, design, assembly, testing and temperature regulation were carried out. This parallel type smoker has 3 main parts, namely the combustion stove, inlet pipe, and smoking cupboard. In the inlet pipe there is a faucet which functions as a control for the smoke output and temperature from the combustion stove to the smoking cupboard. In terms of testing, this tool was tested in several stages, namely trial 1, trial 2, and performance test. After the test is complete, the final stage is carried out, namely equalizing the temperature in each cupboard. The trial phase 1 was carried out with treatment on the operation of the smoke cupboard. Where the stages of operation of all cupboards are carried out simultaneously, then operation of 2 cupboards is carried out and one path is closed alternately. The results showed that the tool experienced problems in the form of unstable temperatures and leaks in the smoker cupboard, so it required patching with silicon. After design improvements have been made, trial 2 and performance testing are continued. Trial 2 was carried out to find out whether the tool still had problems or not before carrying out a performance test. The treatment for trial 2 was the same as that given during trial 1. As a result, the device had no leaks and the temperature was stable and the device was ready to operate at the 15th minute. After that, a performance test was carried out which had the same stages as trials 1 and 2. This is intended to see whether the tool is in accordance with the results during testing or not. After the performance test is carried out, the final stage is to equalize the temperature in each cupboard to produce the same and stable temperature. This equalization is done by adjusting the opening of the faucet valve on the inlet pipe. The results obtained were a parallel type smoker which had 3 smoking cabinets with the same temperature around 37oC. This temperature can used for low smoking temperature.Keywords: Design of Smoker, Parallel, Temperature.

The Application of Six Sigma Framework (Define-Measure-Analyse-Improve-Control) to Improve Product Quality in Water Dispenser Manufacturing Company

This research aims to determine the causes of water dispenser product defects and find the main factors causing defects. This research was conducted in the form of a case study. The data used consists of quantitative data, supported by qualitative data. The analytical method used is Six Sigma, with a focus on the DMAIC method (define, measure, analyze, improve, and control) and sigma values. The population of this research is all water dispenser product equipment. Through observation, interviews and documentation techniques, this research collected data. The data processing method used is DMAIC Six Sigma, with a special focus on the Measure stage. Based on the research results, it was found that the process performance of the water dispenser product was at the level of 4.72 sigma with a DPMO value of 633,732. The most dominant defect occurs in the motor pump. Causes of defects in water dispenser products include human factors (inexperienced operators, errors in reading work instructions, unclear job holders, products not completed on time), materials (parts that do not meet standards, inspection/test equipment that does not function, CBU units that do not conform to standards), methods (products do not meet customer expectations, finished products do not meet standards, inspector operators do not master the use of measuring equipment according to regulations, customer complaints are not handled properly), and environment (hot room conditions, unstable room temperature). The most influential cause and priority for improvement is that customer complaints are not resolved or solutions are sought by the supplier.

A new strategy of dual-material reactors for stable thermal output of sorption thermal battery

Sorption thermal battery driven by air humidity is a promising alternative technology to traditional methods of burning fossil fuels for space heating. Its dominant design of one-material reactor faces technical bottlenecks of unstable discharging thermal output and low energy efficiency. Herein, a new strategy of cascaded dual-material reactors was proposed as a solution, by utilizing their different sorption characterizations at material level and “reaction wave” properties at system level. A proof-of-concept prototype was established, whose main and regulatory reactor were packed with AA-15% LiCl composite and SrBr2·H2O, respectively. Experimental results demonstrated that the regulatory reactor has a strong stabilization function of the unstable output temperature of the main reactor, with the average output temperature fluctuations under 1.5 °C. The discharging/charging energy efficiency was increased by 0.4–1.7 times compared with one-material reactor. The output temperature level and heating power can be simply adjusted by changing the inlet air humidity and air velocity. Moreover, the influences of the lengths of two reactors on the thermal output and system operations were evaluated. Possible strategies to further enhance the multistage utilization of the charging energy were proposed. This new design strategy can contribute to the popularization and application of sorption thermal battery.

Experimental investigation on a screw-type air source heat pump system with air heat absorption defrosting

Defrosting is crucial challenge for air-source heat pump operating in cold and humid climates due to its adverse impact on the heating efficiency. Conventional reverse cycle defrosting method has the disadvantages of reduced heating capacity, inefficient defrosting, and unstable heating temperatures. To address this issue, an Air Heat Absorption Defrosting method based on the reverse Carnot cycle principle was proposed to ensure uninterrupted heating during defrosting. To further validate the technical feasibility and energy-saving potential of the proposed system, a 710.0 kW screw-type air–water heat pump prototype was constructed to carry out control experiments under various conditions. Experimental results showed that, the proposed method achieved an average heating capacity of 315.7 kW during the defrosting process. The cyclic equivalent heating capacity and defrosting correction coefficient of the proposed method were 61.8 kW and 14.4 % higher in comparison with conventional reverse cycle defrosting method, respectively. Thus, the temperature fluctuation of supply water during the defrosting process was reduced by 69 %. In addition, the cumulative COP of Air Heat Absorption Defrosting method was 9.3 % higher than reverse cycle defrosting method, which could be attributed to the fact that the defrosting energy mainly came from air heat absorption. These findings highlight the potential of proposed Air Heat Absorption Defrosting method in addressing heat pump defrosting challenges while offering significant energy-saving benefits.

An E3 ubiquitin ligase CSIT2 controls critical sterility-inducing temperature of thermo-sensitive genic male sterile rice.

Thermo-sensitive genic male sterile (TGMS) lines are the core of two-line hybrid rice (Oryza sativa). However, elevated or unstable critical sterility-inducing temperatures (CSITs) of TGMS lines are bottlenecks that restrict the development of two-line hybrid rice. However, the genes and molecular mechanisms controlling CSIT remain unknown. Here, we report the CRITICAL STERILITY-INDUCING TEMPERATURE 2 (CSIT2) that encodes a really interesting new gene (RING) type E3 ligase, controlling the CSIT of thermo-sensitive male sterility 5 (tms5)-based TGMS lines through ribosome-associated protein quality control (RQC). CSIT2 binds to the large and small ribosomal subunits and ubiquitinates 80S ribosomes for dissociation, and may also ubiquitinate misfolded proteins for degradation. Mutation of CSIT2 inhibits the possible damage to ubiquitin system and protein translation, which allows more proteins such as catalases to accumulate for anther development and inhibits abnormal accumulation of reactive oxygen species (ROS) and premature programmed cell death (PCD) in anthers, partly rescuing male sterility and raised the CSIT of tms5-based TGMS lines. These findings reveal a mechanism controlling CSIT and provide a strategy for solving the elevated or unstable CSITs of tms5-based TGMS lines in two-line hybrid rice.

Numerical simulation of convective heat transfer in the discharging process of external ice-melting ice storage systems

The external ice-melting ice storage system was widely used because of its advantages of reducing peak power consumption, reducing energy consumption and emissions, and fast ice melting speed. However, designing the external ice-melting ice storage system proved to be a challenge, and the structure and flow of the water distribution system needed to be fully considered. In particular, the problem of unstable outlet water temperature limited the practical application of the external melting ice storage system. Aiming at the problem of unstable outlet water temperature, a three-dimensional CFD phase change model was constructed in this paper. By comparing with the experimental data, the impact of varying water flow rates on the thermal and cooling properties of the was investigated. The results indicated that when the water flow rate was 226 ml/min for the system with an ice thickness of 74 mm, the outlet temperature of the ice storage tank was consistently below 5°C, the Nusselt number of ice and water remained constant, and the convective heat transfer effect was improved. The numerical simulation results provided guidance for the design and practical application of the water distribution system of the external melting ice storage system.

Logistic regression in approximation of the results of gas chromatographic analysis of thermally unstable compounds

Regularities and peculiarities of gas chromatographic analysis of thermally unstable compounds were considered on the example of mixture of the reaction products of isopropylbenzene (cumene) free-radical chlorination. The principal constituent in this mixture is (1-chloro-1-methylethyl)benzene, which has the lowest thermal stability, and is partially converted to a-methylstyrene, the only product of its thermal destruction at the chromatograph injector temperatures up to 300 °С. Nevertheless, the results of the study confirms that the gas chromatographic analysis of chloroalkylarenes is possible without their decomposition with the injector temperatures up to 200 °С, even if the analytes contain chlorine atoms at the tertiary carbon atoms and in the “benzylic” positions relative to the aromatic fragment. Similar control of thermal stability of analytes can be recommended for other samples contained potentially unstable constituents. It is shown that thermal decomposition of thermally unstable constituents of samples cannot be revealed from the results of gas chromatographic analysis with capillary columns using variations of their absolute peak areas. Such task can be solved only by using relative peak areas calculated in respect to thermally stable compounds. The dependencies of relative peak areas of unstable constituents vs. temperature (descending), as well as those of their decomposition products (ascending) are characterized by presence of two limits. Low temperature limits correspond to the real content of unstable constituents or their decomposition products is the samples, while the upper limits – to the composition of such samples at their hypothetically complete destruction. Such dependencies can be approximated by logistic regression equation if sampling into capillary columns is carried out at relatively high split ratios (approx. not less than 10 : 1). At lower split ratios the temperature dependencies of peak areas of unstable constituents and products of their transformation are strongly distorted by so-called sample’s composition discrimination effects that make impossible data approximation using logistic regression.