# A Compact Instrument for Temperature-Programming-Assisted Capillary-Nanoliquid Chromatography
## 2 Materials and Methods
### Capillary-NanoLC Instrument Development
#### 2.3.3 Capillary-NanoLC Column Oven  
The capillary-nanoLC furnace (Figure 2) was designed with six key components: a metal body, thermal insulation, a ceramic tube, a cooling system, a resistive heating element, and a temperature sensor. The furnace body was constructed from a stainless steel box measuring 280 mm in length, 40 mm in height, and 40 mm in depth. Thermal insulation was provided by Fiberfrax(r), a silica and alumina fiber blanket known for its ability to withstand high temperatures, with a maximum tolerance of up to 1430 \({}^{\circ}\)C. This material also offers low thermal conductivity and minimal heat storage.  
The heating mechanism comprised a ceramic tube through which the column passed. This tube was externally wrapped with a 0.102 mm diameter, 4 m long nickel-chromium wire featuring a resistivity of 1.0 \(\times\) 10\({}^{-6}\)\(\Omega\cdot\)m. This configuration ensured uniform heat distribution, with the heater delivering 24 W of thermal power when powered at 110 V.  
Figure 2: Photographs of the developed capillary–NanoLC temperature-programmable oven: (**a**) metal body of the oven; (**b**) Fiberfrax® thermal insulation fabric; (**c**) ceramic tube wrapped with resistive nickel–chromium heating wire; (**d**) cooling fan; (**e**) Celeron cooling duct; (**f**) servomotor controlling the cooling windows; (**g**) cooling windows; (**h**) fully assembled oven.  
A rapid cooling system was integrated, utilizing two 25 \(\times\) 25 mm fans connected to the furnace via ducts. Additionally, the cooling system featured a door mechanism composed of a bronze shaft with two Celeron disc-shaped doors operated by a Tower Pro SG90 micro-servomotor. This motor was responsible for opening and closing the doors, assisting in efficient temperature regulation.  
The oven's electronic system comprised four critical circuits: a heater power controller, a temperature sensing circuit, a power supply with mains voltage monitoring, and a driver circuit for activating the cooling system (including door servos and DC fan motors). The furnace's overall operation was managed using a PIC16F877A microcontroller, which communicated with the PC via an RS232 interface.  
Temperature monitoring was achieved using a DM-503 PT-100 platinum resistance temperature detector (RTD) from Labfacility Ltd. (Bognor Regis, UK), with a Class B tolerance. This sensor could measure temperatures up to 500 \({}^{\circ}\)C with an accuracy of around 0.5 \({}^{\circ}\)C within the 0-100 \({}^{\circ}\)C range. In an RTD sensor, the resistance varies with temperature, and its constant current excitation generates an output voltage proportional to the temperature. This signal was then amplified and digitized by the ADC integrated into the microcontroller.  
The heater power was regulated with a control circuit using a MAC8M TRIAC transistor from On Semiconductor. This transistor, mounted on heat sinks, could handle loads of up to 8 A at alternating voltages up to 800 V. It was controlled with a MOC3021 optocoupler from Fairchild, which consisted of a GaAs LED emitter and a light-activated bilateral switch. This ensured reliable and isolated control of the heating element. A synchronization circuit was also implemented to align TRIAC operation with mains cycles, reducing electromagnetic interference, which can be a significant noise source in high-precision laboratory environments.