# A Compact Instrument for Temperature-Programming-Assisted Capillary-Nanoliquid Chromatography
## 1 Introduction  
Liquid chromatography (LC) is an essential analytical technique extensively employed across various fields, including pharmaceuticals, environmental science, food safety, and omics research. The conventional high-performance liquid chromatography (HPLC) system, typically utilizing columns with inner diameters (i.d.) ranging from 2.1 to 4.6 mm, has been the workhorse of analytical laboratories for decades [1]. However, the miniaturization of the technique--capillary LC (i.d. 0.1-0.5 \(\upmu\)m) and nanoLC (i.d. \(<\)0.1 \(\upmu\)m)--offers several significant advantages over traditional HPLC, particularly in terms of chromatographic efficiency, sensitivity, and solvent consumption [2, 3]. Compared to conventional HPLC, miniaturized LC techniques, such as capillary and nanoLC, offer enhanced analytical performance, particularly regarding chromatographic efficiency and detection sensitivity [4]. While particle size remains a key factor influencing column efficiency, reducing the column's inner diameter is critical in improvingchromatographic performance. A smaller inner diameter enhances chromatographic efficiency in several ways. Firstly, it reduces the radial dispersion of the chromatographic band, resulting in narrower eluted peaks. Additionally, in particle-packed columns, the interactions between the tube wall and the packed bed become more significant at smaller diameters, leading to a more ordered chromatographic medium and, consequently, more uniform chromatographic bands [5]. Moreover, monolithic nanoLC columns can be prepared with smaller domain sizes and uniform structures, making them more efficient than their conventional-scale equivalents [6]. Finally, nanoLC can also exploit open tubular columns, which do not exhibit Eddy dispersion due to multiple path effects, potentially outperforming their packed counterparts [7]. Capillary LC and nanoLC also operate at significantly lower flow rates, resulting in less on-column dilution and more concentrated eluted bands. This improves detectability with spectrophotometric and mass spectrometry detectors, even from minuscule sample amounts [8]. Miniaturized LC is an invaluable tool in molecular omics strategies because it handles complex samples and detects minute analyte quantities from small sample volumes. This capability is particularly critical for achieving rapid, sensitive, high-throughput analyses, which are essential in such applications [9]. However, the applicability of miniaturized LC extends beyond omics sciences; any molecule analyzable by conventional HPLC can be analyzed using capillary or nanoLC [10]. Environmental sustainability is another critical advantage of miniaturized LC. With growing concerns over the environmental impact of laboratory practices, the ability of capillary and nanoLC to drastically reduce organic solvent consumption--up to 1000-fold for capillary LC and 10,000-fold for nanoLC. This is achieved by transitioning from traditional flow rates of 0.5-1.0 mL/min to much lower rates of 100 nL/min to 5 \(\upmu\)L/min. Such reductions result in substantial cost savings in solvent procurement and waste management and support industry-wide initiatives to reduce ecological footprints [9]. Although all these features were well established early on, making capillary and nanoLC highly desirable in many research areas, the development of this technique has been slow and strongly limited by the challenges associated with managing reduced extra-column volumes and very low flow rates [11]. Extra-column band broadening becomes much more critical at the reduced scale, and micro/nanoflow rates require precise, accurate, and pulseless solvent delivery instrumentation [2; 3]. The pumps must produce low flow rates (nL-\(\upmu\)L/min) with precision and accuracy. The connecting tubes must have low extra-column volume, and the sample introduction devices and detectors must be compatible with capillary columns to avoid dispersion of the chromatographic band.