Instrument platforms for high-performance thin-layer chromatography

Sample preparation for planar chromatography

“…Sample application using one of several spray‐on devices, such as the one shown in Figure 1, dominates sample application in HPTLC [3, 5]. Extracts and standards in individual vials or a multiwell plate can be applied in any order and different volumes to preselected locations on the layer under keyboard control.…”

“…Planar separation techniques are dominated by TLC, paper chromatography being largely consigned to history except for a few legacy applications in biochemistry and its rebirth as an integral component of low‐cost, on‐site detection microfluidic devices [1–3]. The community of TLC users can be assigned to two groups.…”

“…This has tended to enshrine poor and less‐than‐optimum practices. The second and smaller group is associated with HPTLC using layers prepared with smaller particle sorbents of a more uniform size, chemically bonded phases to expand selectivity, and advanced instrumentation for automation and control of unit operations [3–5]. HPTLC requires a considerable capital investment to support state‐of‐the‐art separations and analysts who use conventional TLC practices have not been sufficiently vocal or interested in advocating for suitable facilities to sperm major growth in HPTLC.…”

“…This is unfortunate as HPTLC has much to offer as a complementary technique to high‐performance liquid chromatography (HPLC) [4]. Growing interest outside of the TLC community is being driven by a higher level of automation with keyboard control of experimental variables [3, 5], direct coupling to MS detection for structure assignment and quantification [3–7], and effects‐directed detection employing chemical, enzymatic, microorganisms, and cell‐based assays for bioactivity reporting [3, 4, 8–11]. The last two areas represent a significant influx of new applications for HPTLC highlighted by an increasing number of literature citations.…”

“…Samples requiring a high peak capacity for their separation are usually better handled by column‐based methods as are samples that require separation mechanisms not commonly available for HPTLC, such as affinity, size‐exclusion, or ion‐exchange due to the limited availability of suitable stationary phases. Applications based on HPTLC tend to be focused on small, neutral compounds separated by normal‐phase chromatography on inorganic oxide sorbents, RP separations on various siloxane‐bonded silica sorbents and cellulose, and by hydrophilic interaction liquid chromatography [3, 4]. Ions and ionizable compounds can be separated using ion‐pair chromatography in the RP mode as well as the separation of anions by ion‐exchange chromatography on 3‐aminoproylsiloxane‐bonded silica layers.…”