# A Compact Instrument for Temperature-Programming-Assisted Capillary-Nanoliquid Chromatography
## 1 Introduction
Despite these challenges, ongoing efforts to address the limitations of miniaturized LC are promising. Advances in instrument design and user training are making the technology more accessible. Over the past 20 years, significant progress has been made in developing instruments designed explicitly for miniaturized LC, resulting in various commercially available instruments, columns, and consumables [2; 3]. Additionally, capillary and nanoLC facilitate the miniaturization of instruments, leading to the emergence of diverse small-footprint and portable LC systems [12]. Portable miniaturized LC instruments, characterized by their simplicity and cost-effectiveness, are gaining traction in various fields. These portable systems offer rapid, on-site analysis capabilities, which are handy for environmental monitoring and field-based studies [13]. In such applications, portable miniaturized LC instruments help reduce issues related to sample degradation and contamination during transport, ensuring more reliable and timely data. An additional, less explored advantage of miniaturized liquid chromatography is using temperature programming as a selectivity modulation factor to enhance efficiency and resolution. Selectivity can be fine-tuned in isocratic elution mode by applying temperature gradients. Isocratic elutions eliminate the need for column reconditioning between analyses and utilize straightforward instrumentation, as they can be performed with a single pump. This simplicity facilitates the design and construction of more accessible LC instruments. A change in the analysis temperature causes pronounced effects on several parameters, such as viscosity, solubility, diffusivity, and vapor pressure, influencing column efficiency, resolution, back pressure, selectivity, retention time, peak shape, and the properties of stationary phases [14]. In conventional LC, heat flow through the column's cross-section is inefficient, making temperature programming unfeasible. However, heat flow is fast and uniform through the chromatographic bed at the miniaturized scale, particularly with capillary-nanoLC columns (i.d. <300 \(\upmu\)m). Consequently, the mobile phase rapidly responds to temperature changes, making temperature programming a viable alternative [15]. Temperature programming in nanoLC has been previously demonstrated multiple times [16]. For instance, a 5 \({}^{\circ}\)C increase in column temperature can be comparable to a 1% acetonitrile change in the mobile phase, and a 3.75 \({}^{\circ}\)C rise is similar to a 1% methanol variation [17]. Therefore, the effects of temperature programming in miniaturized LC are akin to those observed when applying a solvent gradient. This advantage is particularly useful in designing and constructing novel miniaturized LC instruments. By using temperature programming, separations can be conducted in isocratic mode, thus simplifying the instrument by eliminating the need for complex gradient pumping systems and significantly reducing costs. This paper describes the construction and performance of a lab-made, compact instrument designed for temperature-programmed nanoLC. This small-footprint platform comprises a high-pressure syringe-type pump, a miniaturized oven capable of performing isothermal and temperature programming, and a capillary UV-Vis detector compatible with capillary and nanoLC. By detailing this instrument's design, construction, and application, we aim to demonstrate its potential as a viable alternative to conventional HPLC for routine analytical purposes. The successful implementation of this technology could pave the way for broader adoption of miniaturized LC in various industries, promoting more sustainable and efficient analytical practices.