Ultrathin-layer Chromatography Research Articles

A magnetic field augmented ultra-thin layer chromatography coupled surface enhanced Raman spectroscopy separation of hemozoin from bacterial mixture

Malaria is considered as one the most widespread disease with highest possibility of co-infection at all levels of the disease prognosis. Rapid detection and discrimination of malaria from other co-infections remains a challenge. Hemozoin is a metabolic biproduct of malaraia possessing paramagnetic property due to presence of iron at its centre. Here, we report a label free, rapid and highly sensitive magnetic field based ultra-thin layer chromatography (UTLC) coupled with surface enhanced Raman spectroscopy (SERS) technique for detection and separation of hemozoin from a bacterial mixture. Highly optimized silver nanorods chip fabricated using glancing angle deposition (GLAD) is explored for the UTLC-SERS separation. These chips possessing channel like characteristic and high surface to the volume ratio serve as excellent UTLC plates. The magnetic nature of hemozoin has been exploited for its separation from the mixture of P. aeruginosa (Gram-negative) and S. aureus (Gram-positive) by allocating a 0.6 T magnet over the UTLC flow setup. The solvent front migrated approximately to a distance of 13 mm from the sample point due to the magnetic environment. Spatially resolved SERS data was collected along the mobile phase and separation of mixture was confirmed. Further, staining of hemozoin, P. aeruginosa and S. aureus was done using methylene blue, acridine orange and rhodamine 6 G respectively. The separation was confirmed for the stained analytes. The present developed method provides plate height as low as 18 µm and hemozoin detection limit as <10 parasites/mL. Therefore, we establish a highly specific and sensitive technique capable of separating small amounts of bioanalytes, aiding in the removal of co-infections from the disease at a very early stage of infection.

Photonic Crystal Enhanced SERS Detection of Analytes Separated by Ultrathin Layer Chromatography Using a Diatom Frustule Monolayer

AbstractDiatoms are single‐celled algae that biologically fabricate nanostructured silica shells with ordered pore arrays called frustules that resemble a 2D photonic crystal. A monolayer of Pinnularia frustules isolated from cell culture is deposited on a glass substrate and then conformally coated with silver nanoparticles (AgNPs) to serve as a nanostructured thin film for ultrathin layer chromatography (UTLC). Malachite green and Nile red are resolved in toluene mobile phase and the separated analytes are profiled micro‐Raman spectroscopy, where plasmonic AgNPs provide surface‐enhanced Raman scattering (SERS). The AgNP‐diatom frustule monolayer improves SERS detection of malachite green by an average factor of 1.8 ± 0.1 over the plasmonic AgNP layer on glass. Analysis of hot spots on the AgNP‐diatom frustule monolayer reveals that nearly 20% of the SERS active area intensifies the SERS signal at least tenfold over the SERS signal for AgNP on glass. Diatom‐SERS enhancement is attributed to guided‐mode resonances of the Raman laser source, which in turn further enhances the localized surface plasmonic resonance from AgNPs. Overall, the AgNP‐diatom frustule monolayer thin film is a new functional material that uniquely enables separation of analytes by UTLC, quantitative SERS detection of separated analytes, and photonic enhancement of the SERS signals.

Development of a new particulate 4-μm adsorbent layer for ultrathin-layer chromatography (miniaturized chromatogram)

The performance of particulate layers of a smaller particle size than given HPTLC plates was investigated. However, reducing the particle size and thus interporous space, the capillary flow is substantially reduced. For the first time, optimizations led to the successful use of a layer made of mainly 4-μm irregular silica gel particles as stationary phase in planar chromatography. Layer thicknesses of 50 and 70 μm were studied to suit especially for ultrathin-layer chromatography (UTLC). Along with it, the chromatographic fingerprint was miniaturized by 75%. The required development time and developing distance were reduced up to 50%. A typical 35-mm separation took less than 10 min. The limit of detection was improved by a factor of up to 3. Further chromatographic performance data, such as separation number (peak capacity), resolution and analytical response proved the suitability of the particulate UTLC layer. A direct transferability and miniaturization of established HPTLC methods to the UTLC dimension was aimed at. This was successfully demonstrated for eight quite different separations, i.e. food dyes, polycyclic aromatic hydrocarbons, steviol glycosides in cough drops and sweetener tablets, preservatives in shrimp-surimi salad, gingerol in ginger-containing products, 5-hydroxymethylfurfural in honey, tanshinones in Salvia miltiorriza extracts and monacolin K in fermented red rice food supplements. The direct method transfer, mainstream usability and fast analyses at low running costs are crucial features of the developed UTLC plate. Profiting from such advantages, the miniaturized fingerprint shows potential to shift the field of HPTLC towards UTLC. Nevertheless, the full separation potential will first be exploited with tailored, miniaturized instrumentation capable to operate with the reduced layer thickness and UTLC format.

Office Chromatography: Miniaturized All-in-One Open-Source System for Planar Chromatography.

Current high-performance-thin-layer-chromatography instrumentation is offline and stepwise automated. However, moderate miniaturization offers many advantages and together with the transfer of modern print and media technologies to the field of chromatography (office chromatography) it opens up new avenues. This is demonstrated in an all-in-one open-source system developed for planar chromatography and especially for ultrathin-layer chromatography. Using an InkShield board to control a thermal inkjet cartridge, picoliter drops were printed at a resolution of 96 dpi on the adsorbent layer. Using Marlin, a popular firmware in 3D printing, Cartesian movement of the print head was made possible for full control of the printing process. Open-source software was developed to control the device in each operation step. Sample solutions and mobile phase were inkjet-printed, exemplarily shown for the analysis of dye- or paraben-mixture solutions. Light-emitting diodes (LEDs) were investigated for documentation. For example, deep UV LEDs gave access to 254 nm light, and RGB LEDs gave access to the visible-light range. Calibration functions with correlation coefficients superior to 0.999 were obtained by videodensitometry. The developed modular open-source hardware was compact (26 × 31 × 26 cm3), light (<3 kg), and affordable (€810). For the given analyses, the footprint of current instrumentation needed was miniaturized by a factor of 9. The highly reduced material design complies with green chemistry and lean laboratory. The design and instruction to reproduce the all-in-one open-source system were made freely available at https://github.com/OfficeChromatography . It is intended to boost progress and understanding by the nature of do it yourself.

A high‐performance multifunctional substrate of ultrathin‐layer chromatography (UTLC) and surface‐enhanced Raman scattering (SERS) for rapid biochemical mixture screening

AbstractWe present a multifunctional substrate of ultrathin‐layer chromatography (UTLC) and surface‐enhanced Raman scattering (SERS), which enables analytes separation and label‐free detection simultaneously. This integrated substrate is composed of silicon nanowires array (SiNWA), decorated with silver nano‐dendrites (AgNDs). This SiNWA is fabricated by a facile and low‐cost metal‐assisted chemical etching process, and the AgNDs are then decorated onto SiNWA by chemical reduction process. These AgNDs provide abundant hot spots by inducing strong localized electric field, which is confirmed by finite‐difference time‐domain simulation calculations. With the optimized multifunctional substrate, the screening of melamine is successfully validated. The high linear dependence of signal intensity and melamine concentrations from 15 to 1,500 ppm with small deviation was carried out by our developed UTLC–SERS substrate, providing a great potential for quantitative detection. Besides, the SERS signals further show a low relative standard deviation of 8.7%, benefited from the calibration by a peak located at 520 cm−1 of silicon. In short, such a low‐cost, high‐stable multifunctional substrate of UTLC and SERS can be readily employed for practical applications of rapid biochemical mixture screening.

Separation of PEGylated Gold Nanoparticles by Micellar Enhanced Electrospun Fiber Based Ultrathin Layer Chromatography.

Gold nanoparticles (AuNPs) are of great interest in many fields, especially in biomedical applications. Thiol terminated polyethylene glycol (PEG) is the most widely used polymer to increase the biocompatibility of nanoparticle therapeutics. Herein, a rapid method for separation and characterization of PEGylated AuNPs on an ultrathin layer chromatographic (UTLC) plate using electrospun polyacrylonitrile (PAN) nanofibers as the stationary phase is described. AuNPs with sizes ranging from 10 to 80 and 30 nm AuNPs coated with various molecular weight of PEG (2, 5, 10, and 20 kDa) were all successfully separated by UTLC using optimized conditions. The fabrication of electrospun UTLC is simple, fast, and inexpensive. The UTLC, with much thinner sorbent layer (10× thinner than traditional TLC) and small fiber size (∼300 nm), requires minimal mobile phase solvent and provides faster separation and higher resolution compared to other separation methods for AuNPs. AuNPs with different sizes and different PEG molecular weights were well separated within 5 min with lowest plate height <2 μm and resolution value >1.5. As an example of this method, the size transformation of AuNPs in serum protein was determined quantitatively.

Rapid Biochemical Mixture Screening by Three-Dimensional Patterned Multifunctional Substrate with Ultra-Thin Layer Chromatography (UTLC) and Surface Enhanced Raman Scattering (SERS)

We present a three-dimensional patterned (3DP) multifunctional substrate with the functions of ultra-thin layer chromatography (UTLC) and surface enhanced Raman scattering (SERS), which simultaneously enables mixture separation, target localization and label-free detection. This multifunctional substrate is comprised of a 3DP silicon nanowires array (3DP-SiNWA), decorated with silver nano-dendrites (AgNDs) atop. The 3DP-SiNWA is fabricated by a facile photolithographic process and low-cost metal assisted chemical etching (MaCE) process. Then, the AgNDs are decorated onto 3DP-SiNWA by a wet chemical reduction process, obtaining 3DP-AgNDs@SiNWA multifunctional substrates. With various patterns designed on the substrates, the signal intensity could be maximized by the excellent confinement and concentrated effects of patterns. By using this 3DP-AgNDs@SiNWA substrate to scrutinize the mixture of two visible dyes, the individual target could be recognized and further boosted the Raman signal of target 15.42 times comparing to the un-patterned AgNDs@SiNWA substrate. Therefore, such a three-dimensional patterned multifunctional substrate empowers rapid mixture screening, and can be readily employed in practical applications for biochemical assays, food safety and other fields.

Performance of Electropun Polyacrylonitrile Nanofibrous Phases, Shown for the Separation of Water-Soluble Food Dyes via UTLC-Vis-ESI-MS.

Research in the miniaturization of planar chromatography led to various approaches in manufacturing ultrathin-layer chromatography (UTLC) layers of reduced thickness (<50 µm) along with smaller instrumentation, as targeted in Office Chromatography. This novel concept merges 3D print & media technologies with miniaturized planar chromatography to realize an all-in-one instrument, in which all steps of UTLC are automated and integrated in the same tiny device. In this context, the development of electrospun polyacrylonitrile (PAN) nanofiber phases was investigated as well as its performance. A nanofibrous stationary phase with fiber diameters of 150–225 nm and a thickness of ca. 25 µm was manufactured. Mixtures of water-soluble food dyes were printed on it using a modified office printer, and successfully separated to illustrate the capabilities of such UTLC media. The separation took 8 min for 30 mm and was faster (up to a factor of 2) than on particulate layers. The mean hRF values ranging from 25 to 90 for the five food dyes were well spread over the migration distance, with an overall reproducibility of 7% (mean %RSD over 5 different plates for 5 dyes). The individual mean plate numbers over 5 plates ranged between 8286 and 22,885 (mean of 11,722 over all 5 dyes). The single mean resolutions RS were between 1.7 and 6.5 (for the 5 food dyes over 5 plates), with highly satisfying reproducibilities (0.3 as mean deviation of RS). Using videodensitometry, different amounts separated in parallel led to reliable linear calibrations for each dye (sdv of 3.1–9.1% for peak heights and 2.4–9.3% for peak areas). Coupling to mass spectrometry via an elution head-based interface was successfully demonstrated for such ultrathin layers, showing several advantages such as a reduced cleaning process and a minimum zone distance. All these results underline the potential of electrospun nanofibrous phases to succeed as affordable stationary phase for quantitative UTLC.

Abstract 4208: Development of 18F-IL2: a PET radiotracer for imaging activated T-cells

Abstract Introduction: Activation of T-cells is accompanied by a strong up-regulation of interleukin-2 (IL2) receptor (CD25). Therefore PET imaging of IL2 receptors might be a suitable imaging biomarker for T-cell activation. 18F-IL2 PET could detect CD25-positive T-cells and the migration of these T-cells to distant sites of inflammation in SCID mice subcutaneously injected with human peripheral blood mononuclear cells1 and NOD mice with insulitis. Also a strong correlation was found between the accumulation of 18F-IL2 and the number of injected activated T-cells in immune-competent rats.2 In tumor bearing mice, 18F-IL2 PET could detect treatment-induced accumulation of activated T-cells in the tumor following local radiotherapy and/or vaccination. Cancer immunotherapy is increasingly obtaining a place in clinical practice. However not all patients benefit. A biomarker for upfront or early response prediction for these immunotherapies might support patient selection before and during therapy. Potentially 18F-IL2 PET might serve this purpose. Therefore we aimed to accommodate the production of 18F-IL2 for use in clinical imaging studies. Material and methods: In order to produce a GMP-compliant tracer the production is being implemented on the Eckert &amp; Ziegler PharmTracer synthesis module. In this synthesis module, disposable cassettes, reactors and vials are used to avoid cross-contamination between productions. First the prosthetic group N-succinimidyl 4-fluorobenzoate (18F-SFB) is produced in 3 steps from cyclotron-produced 18F-fluoride. Subsequently, 18F-SFB is conjugated to human recombinant IL2 (Proleukin®). Various methods for synthesis and purification of 18F-SFB have been evaluated. Also purification of 18F-IL2 has been optimized. Quality control has been performed using ultra performance liquid chromatography (UPLC) and Thin Layer Chromatography (TLC). Results: 18F-SFB was successfully synthesized with the Eckert &amp; Ziegler PharmTracer synthesis module with decay-corrected radiochemical yields comparable to literature (range 28-64%). Major challenges have been encountered, most importantly regarding the purification of the 18F-SFB and 18F-IL2, stability of the IL2 and specific activity. The activated ester 18F-SFB was purified by high performance liquid chromatography (HPLC) to remove any impurities that could interfere with the conjugation. 18F-IL2 has been purified using PD-10 columns with PBS containing 0.05% SDS as mobile phase. Conclusions: Several challenges for the GMP-compliant production of 18F-IL2 have been overcome. In the near future this tracer will be used in preclinical and clinical studies to non-invasively image activated T-cells before and during cancer immunotherapy. This can provide insight in the effects of cancer immunotherapy on the immune response.

Miniaturization of Instrumental Planar Chromatography with Focus on Mass Spectrometry

The universal trends to miniaturization and to automation of technologies affect the further development of analytical instrumentation and methodologies. In planar chromatography, these trends are characterized by decreasing dimensions and thickness of the stationary phase and the development of respectively tailored equipment. The miniaturization of instrumental planar chromatography is reflected in the interdisciplinary office chromatography concept, in which achievements in office technologies (print and media technologies) and miniaturized layer developments are integrated. The office chromatography concept stimulates research towards miniaturization and will at last implement a fully online miniaturized system. The use of print techniques is still at its infancy in separation science, whereas printing of materials already became an accepted tool in the life sciences. Commercially, available printers were used for sample application on miniaturized plates and were stepwise modified for a precise and quantitative performance. Further miniaturization attempts led to miniaturized layers with different physical and chromatographic properties. The method transfer to such ultrathin-layer chromatography (UTLC) plates demonstrated the synergetic potential of this instrumental concept. Detection and evaluation tools have to be adjusted and integrated, too. Since the beginning of this millennium, several ionization techniques have been introduced or improved, and paved the way for mass spectrometry (MS) directly from miniaturized surfaces. UTLC was already coupled to MS via several ion source interfaces, such as secondary ionization, matrix-assisted laser desorption and ionization, electrospray ionization, desorption electrospray ionization and direct analysis in real time. However, the hyphenation to targeted, scanning or imaging MS still requires adaptations and methodic efforts to utilize UTLC layers.

Fabrication of nanofiber stationary phases from chopped polyacrylonitrile co-polymer microfibers for use in ultrathin layer chromatography of amino acids

Polyacrylonitrile co-polymer microfibers of diameter 12.5 μm was used for electrospinning to produce nanofibers and then used as a stationary phase in UTLC for on-plate identification and separation of amino acid from drug sample.

Challenges in quantitative high-performance thin-layer chromatography — Part 1: Influence of densitometric settings on the result

There is no doubt that high-performance thin-layer chromatography (HPTLC) can be applied as a quantitative method if the technique is properly used. Densitometry is a commonly used detection mode for quantitation in HPTLC. The influence of instrumental settings on signal intensity, peak resolution, and peak positioning was rarely described in literature. Especially, quantitation of adjacent substance zones was critical when improper combinations of these settings merge. Future trends regarding ultrathin-layer chromatography and hyphenation to scanning or imaging mass spectrometry required the consideration of these delicate points. The influence of different instrumental settings on the obtained signal intensities was demonstrated for four separated parabens (each 150 ng band−1). The maximum mean signal deviations of all four compounds were 6.9% by the optical system, 16.8% by the scan slit dimension, 7.5% by the scan speed, and 1.5% by the data resolution. The influence of these settings on the quantitat...

Microfabrication, separations, and detection by mass spectrometry on ultrathin-layer chromatography plates prepared via the low-pressure chemical vapor deposition of silicon nitride onto carbon nanotube templates

Microfabrication of ultrathin-layer chromatography (UTLC) plates via conformal deposition of silicon nitride by low-pressure chemical vapor deposition onto patterned carbon nanotube (CNT) scaffolds was demonstrated. After removal of the CNTs and hydroxylation, the resulting UTLC phase showed no expansion or distortion of their microfeatures and the absence/reduction of remaining nitrogenic species. Developing time of a mixture of lipophilic dyes on this UTLC plates was 86% shorter than on high-performance thin-layer chromatography (HPTLC) plates. A water-soluble food dye mixture was also separated resulting in low band broadening and reduced developing time compared to HPTLC. For the latter example, mobile phase optimization on a single UTLC plate consisted of 14 developments with different mobile phases, each preceded by a plate prewashing step. The same plate was again reused for additional 11 separations under varying conditions resulting in a development procedure with a mean separation efficiency of 233,000theoretical plates/m and a reduced mobile phase consumption of only 400μL. This repeated use proved the physical robustness of the ultrathin layer and its resistance to damage. The layer was highly suited for hyphenation to ambient mass spectrometry, including desorption electrospray ionization (DESI) mass spectrometry imaging and direct analysis in real time (DART) mass spectrometry.

Detection of polycyclic aromatic hydrocarbons from cooking oil using ultra-thin layer chromatography and surface enhanced Raman spectroscopy

The combinatory use of on-chip ultra-thin layer chromatography (UTLC) and surface enhanced Raman spectroscopy (SERS) has been demonstrated to detect mixtures of hazardous food contaminants, polycyclic aromatic hydrocarbons (PAHs), from cooking oil samples. After a simple acetonitrile extraction step, the organic phase was directly applied to the chemically modified SERS-active silver nanorod (AgNR) substrate without further cleanup, and subjected to UTLC separation. The spectral interference from co-extracted oil residues was mitigated by UTLC, and the SERS detection limits were found to be equivalent to or lower than those found in standard PAH solutions. The interference from the oil matrix was also quantitatively assessed, and the PAH extraction procedure was optimized for UTLC-SERS. This UTLC-SERS strategy provides a simple but effective method for on-chip sample cleanup and sensing from complex sample matrices.

Planar Electrochromatography Using an Electrospun Polymer Nanofiber Layer

Electrospun polymer nanofiber stationary phases were examined for their application to planar electrochromatography (PEC). Separations were performed on polyacrylonitrile nanofiber ultra-thin-layer chromatography (UTLC) plates in 1-2 min using a ternary mobile phase. The influences of buffer concentration and pH, ratio of organic modifier, and development time on analyte migration distances were studied. Band broadening in this system was studied as a function of distance. The plate height initially decreased and then plateaued with a minimum plate height value as low as 11 μm. Nanofiber alignment considerably increased analyte migration rate, but larger spot sizes were noted when nearly complete fiber alignment was used. The easily tunable stationary phase thickness can be tailored to a given separation, where thinner layers promote faster separations and thicker layers are ideal for more complex mixtures. Compared to UTLC, PEC offers unique selectivity and decreased analysis time (>4 times faster over 15 mm). Results for a two-dimensional separation using UTLC and PEC are also reported. These rapid separations required 11 min using a 40 × 40 mm plate and exhibited a significant increase in separation number (70-77).

Silica-based nanofibers for electrospun ultra-thin layer chromatography

Nanofibrous silica-based stationary phases for electrospun ultra-thin layer chromatography (E-UTLC) are described. Nanofibers were produced by electrospinning a solution of silica nanoparticles dispersed in polyvinylpyrrolidone solutions to create composite silica/polymer nanofibers. Stationary phases were created from as-spun nanofibers, or the nanofibers were heated either to crosslink the polyvinylpyrrolidone or to calcine and selectively remove the polymer. As-spun, crosslinked, and calcined nanofibers with similar mat thicknesses (23–25μm) were evaluated as stationary phases for E-UTLC separations of laser dyes and amino acids and compared to commercial silica TLC plates. As-spun nanofiber plates offered fast mobile phase velocities, but like other polymer-based nanofibers, separations were only compatible with techniques using nonsolvents of the polymer. Crosslinked nanofibers were not as limited in terms of chemical stability, but separations produced tailed spot shapes. No limitations in terms of mobile phases, analyte solvents, and visualization techniques were observed for calcined nanofibers. Highly efficient separations of amino acids were performed in 15mm on calcined nanofiber plates, with observed plate heights as low as 8.6μm, and plate numbers as large as 1400. Additional alignment of the nanofibers provided shorter analysis times but also larger spot widths. The extension of stationary phases to silica-based nanofibers vastly expands the range of mobile phases, analyte solvents, and visualization techniques which can be used for E-UTLC separations.

Carbon nanotube and carbon nanorod-filled polyacrylonitrile electrospun stationary phase for ultrathin layer chromatography

The application of carbon nanotube or nanorod/polyacrylonitrile (PAN) composite electrospun nanofibrous stationary phase for ultrathin layer chromatography (UTLC) is described herein. Multi-walled carbon nanotubes (MWCNTs) and edge-plane carbon (EPC) nanorods were prepared and electrospun with the PAN polymer solution to form composite nanofibers for use as a UTLC stationary phase. The analysis of laser dyes demonstrated the feasibility of utilizing carbon nanoparticle-filled electrospun nanofibers as a UTLC stationary phase. The contribution of MWCNT or EPC in changing selectivity of the stationary phase was studied by comparing the chromatographic behavior among MWCNT–PAN plates, EPC–PAN plates and pure PAN plates. Carbon nanoparticles in the stationary phase were able to establish strong π–π interactions with aromatic analytes. The separation of five polycyclic aromatic hydrocarbons (PAHs) demonstrated enhanced chromatographic performance of MWCNT-filled stationary phase by displaying substantially improved resolution and separation efficiency. Band broadening of the spots for MWCNT or EPC-filled UTLC stationary phases was also investigated and compared with that for pure PAN stationary phases. A 50% improvement in band dispersion was noted using the MWCNT based composite nanofibrous UTLC plates.

A New Nanostructured Stationary Phase for Ultra-Thin Layer Chromatography: A Brush-Gel Polymer Film

We report here on the fabrication and the characterization of a new stationary phase for ultrathin layer chromatography (UTLC) based on a brush-gel polymer film obtained by cross-linking poly(glycidyl methacrylate) and di(ethylene glycole)dimethacrylate. The use of polymer brushes to design ultra thin layer chromatography plates opens interesting perspectives. Very thin polymer films can be covalently grafted on a glass surface with virtually any chemical functionality. By selecting and/or chemically modifying suitable monomers, stationary phases characterized by high affinity for specific substances can be accurately tailored. The structure of the brush gel formed on glass substrates was characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Atomic Force Microscopy (AFM) and Field-Emission Scanning Electron Microscopy (FESEM). The efficiency of poly(GMA-co-DEGDMA)-NH2 UTLC stationary phase compares very well with that of silica-gel TLC and other UTLC devices. However, the separation of a fluorescent dyes mixture with our UTLC device occurs faster and with less solvent compared to typical TLC methods. In addition the same plate can be re-used several times for multiple analyses without any reduction of the separation efficiency.

Ultrathin-layer chromatography on SiO2, Al2O3, TiO2, and ZrO2 nanostructured thin films

We explored four different inorganic oxides and determined their merits in miniaturized planar chromatography. Despite progression of chromatographic techniques over several decades, such alternatives to traditional planar silica gel stationary phases have not been fully evaluated. Glancing angle deposition (GLAD) provided an excellent platform for engineering nanostructured thin films in these materials for ultrathin-layer chromatography (UTLC). Separations of carotenoids and synthetic food dyes were used to investigate the attributes of SiO2, Al2O3, TiO2, and ZrO2 GLAD UTLC media. These anisotropic high surface area thin films possessed similar channel-like features but different chromatographic properties. TiO2 and ZrO2 media were especially interesting since analyte retention could be modified through simple oxidation heat treatments and UV irradiation. Generally, oxidation reduced analyte retention while UV exposure increased retention. Changes in retention factor as large as ΔhRF∼40 (for Acid Red 14 on titanium oxide) were achieved. Food dye mixtures were applied using consumer inkjet printers as per the Office Chromatography concept and separation performance was quantified using advanced video instrumentation designed for miniaturized plates. Enhanced time-resolved UTLC methods were used to calculate figures of merit from recorded dye separation videos. Small theoretical plate heights (<4μm) and low limits of detection (<2ng per zone for the food dye tartrazine) were measured. The combination of engineered GLAD UTLC plates, inkjet application of analyte spots, time-resolved UTLC, and custom analysis algorithms enabled some of the best performance achieved on GLAD UTLC layers. Separations on the inorganic oxide thin films were also successfully hyphenated with electrospray ionization mass spectrometry for the first time. This investigation demonstrates the utility of alternative inorganic oxide GLAD UTLC media and probes avenues of expanding the capabilities of miniaturized planar chromatography.

Ultrathin-Layer Chromatography (UTLC)

Ultrathin-layer chromatography (UTLC) differs from high-performance thin-layer chromatography (HPTLC) and from thin-layer chromatography (TLC) in two basis things: the layer thickness, and the migration distances of the analytes. UTLC has a monolithic or a nanostructured stationary silica gel phase bound directly to the glass plates. Layer thickness in UTLC is 10 μm, instead of 100–250 μm in HPTLC. Migration distances are in the range of 1–3 cm for UTLC, instead of 8–10 cm for HPTLC. Therefore, the major advantages of UTLC over HPTLC and TLC are the shorter development times and higher separation efficiency and sensitivity. Moreover, separations on UTLC plates require smaller reagent and sample volumes. However, the UTLC plates are very difficult to manage with the TLC and HPTLC equipment currently available. Therefore, the next challenge in this area is the development of an inexpensive solution with appropriate instrumentation (sensitive optical scanners and sample application systems). UTLC had been used for separations of many compounds, e.g., pharmaceutically active ingredients, pesticides, plasticisers, natural products, and other chemical substances.