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The evolution of supercritical fluid chromatography (SFC) instrumentation, improved detection capability, and expanded modifier range has led to extending the reach of SFC to the analysis of a broader spectrum of analytes beyond enantioselective separations. However, preparative SFC has yet to see the same technological revitalization, especially in regards to the purification of highly polar analytes. Enhanced fluidity liquid chromatography (EFLC) has been demonstrated as one of the ways to extend the applicable range of SFC instrumentation to highly polar analytes such as proteins, carbohydrates, and nucleotides. Despite recent applications of EFLC for challenging mixtures of hydrophilic metabolites and analogs, its viability in preparative purification, which is of great importance to the pharmaceutical industry, remains unknown. Herein, multiple chromatographic parameters that are critical to achieve feasible EFLC purification methods were investigated, including system pressure as a function of modifier composition (for several MeOH:H2O ratios), effect of diluent injection conditions on peak shape, and optimization of mass load with diluent composition. The usage of 50% acetonitrile or methanol diluents provided the most volumetric loading capacity. In the case of sucrose, leveraging higher analyte solubility in water proved to be more favorable than the volumetric loading capacity of diluents with higher organic content. In fact, an 80 mg injection of sucrose was possible on a 2 cm preparative HILIC column with minimal peak shape degradation. The combined information led to the successful demonstration of EFLC for the preparative separation of sugars using readily available MS-directed SFC instrumentation.

Vacuum ultraviolet (VUV) detector for gas chromatography (GC) provides qualitative spectral information from 125 nm to 240 nm. In this article, this information was applied to facilitate the development of a GC method for challenging pharmaceutical applications. Seven organic solvents were screened for trace level water content using VUV detection at 168 nm, and the results were used to identify n-hexane as a suitable diluent for 4-ethoxy-1,1,1-trifluoro-3-buten-2-one (ETFBO), a water reactive compound. Selective detection of compounds of interest was demonstrated by varying detection wavelengths. All compounds were detected at 145 nm except for one unknown impurity, which co-eluted with n-hexane solvent. This impurity was detected at 225 nm, where n-hexane has no absorbance. In addition, the VUV spectra were used to: 1) accurately track peaks during early method development; 2) detect co-eluting peaks; 3) match peak identity in a sample vs. a standard; and 4) assess peak purity. With the universal detectability, qualitative spectral information and ease of use, VUV will become a versatile tool for GC for both method development and routine analysis.

A semi-preparative high-resolution system based on twin column recycling liquid chromatography was built. The integrated system includes a binary pump mixer, a sample manager, a two-column oven compartment, two low-dispersion detection cells, and a fraction manager (analytical). It addresses challenges in drug/impurity purification, which involve several constraints simultaneously: (1) small selectivity factors (α 1.2, poor resolution), (2) mismatch of elution strength between the sample diluent and the eluent causing severe band fronting or tailing, (3) diluent-to-eluent mismatch of viscosity causing viscous fingering and unpredictable band deformation, (4) low abundance of the impurity relative to the active pharmaceutical ingredient (API) (1/100), and (5) yield and purity levels to be larger than 99% and 90%, respectively. The prototype system was tested for the preparation of a trace impurity present in a concentrated solution of an API, estradiol. The ultimate goal was to collect ∼1 mg of impurity (90% purity) for unambiguous structure elucidation by liquid state nuclear magnetic resonance (NMR 600 MHz and above). First, the particle size (3.5 μm) used to pack the 4.6 mm × 150 mm long twin columns is selected so that the speed-resolution of the recycling process is maximized at 4000 psi pressure drop. Next, the production rate of the process is also maximized by determining the optimum number (7) of cycles and the corresponding largest sample volume (160 μL) to be injected. Finally, the process is fully automated by programming the time events related to (1) sample cleaning, (2) transfer of the targeted impurity from one to the second twin column, and (3) impurity collection. The process was tested without interruption during one week for the collection of a trace impurity (α = 1.166, strong acetonitrile-methanol sample diluent, concentration ∼2 mg/L) from a concentrated (10 g/L) stock solution (60 mL total) of estradiol. The process enriches the impurity content relative to the API by about a factor ∼5000. For the lack of a sufficient collected amount (∼120 μg only) of the pure impurity (purity 50% only), NMR experiments could not provide reliable results. Instead, the combination of LC-MS (single ion monitoring) and UV absorption spectra (λ

Benefits and limitations of HILIC were studied for the analysis of extreme polar organic contaminants in aqueous environmental matrices. A sensitive analytical method was developed and validated for the detection of 11 pharmaceuticals, 15 pharmaceutical metabolites and transformation products and the artificial sweetener acesulfame in aqueous environmental samples. The analytical method consisted of a simple and non-specific sample preparation based on freeze-drying followed by detection with large injection volume (70 μL) zwitterionic HILIC-ESI-MS/MS. Robustness studies showed a high sensitivity of the retention times and peak shapes to variations of the acetonitrile/water ratio of both the eluent and the diluent. Thus, a thorough sample and eluent preparation is required to obtain reproducible results. Extreme matrix effects of >200% were observed for emtricitabine and acyclovir, which could be traced to the co-elution of nitrate and chloride, respectively. These matrix effects and those of other analytes could be efficiently compensated by using deuterated, 13C and 15N-labeled internal standards. The developed method was able to detect the selected 27 analytes in treated wastewater, surface water and groundwater down to limit of quantification (LOQ) in the lower ng/L range. Appreciable concentrations were detected, ranging up to 110 μg/L (guanyl urea) in treated wastewater, up to 5.1 μg/L (oxipurinol) in surface water and up to 6.1 μg/L (acesulfame) in groundwater. In a German drinking water, only the X-ray contrast medium diatrizoate and the artificial sweetener acesulfame were quantified above LOQ with 0.19 μg/L and 0.35 μg/L, respectively.

We evaluated at-column dilution (ACD) as a possible approach to reduce peak distortion caused by the injection of strong solvents in preparative hydrophilic interaction chromatography (HILIC). Three model compounds, namely uridine, cytidine and guanosine were selected and injected either in conventional or ACD conditions, using various proportions of water and acetonitrile in the sample diluent. Plate number and peak capacity were systematically investigated under both isocratic and gradient elution conditions, respectively. In isocratic conditions, ACD was found to provide higher plate numbers with sample diluent containing more than 40% water, but lower plate numbers with injections of less than 40% water, in comparison to a conventional injection system at the preparative scale. These contrasting results were attributed to the fact that i) efficiency was fundamentally reduced in ACD, due to the low make-up flow rate that was used to flush the injection loop, but ii) the trend was reversed for highly aqueous injection thanks to the capacity of ACD to maintain similar efficiency regardless of the injection solvent. On the other hand, peak capacity was comparable between ACD and conventional systems in gradient elution for injections containing low amounts of water. However, ACD became increasingly advantageous as the proportion of water in the injection solvent and/or the injection volume increased. This was confirmed by the separation of a plant root aqueous extract. Altogether, our findings suggest that ACD is beneficial both in isocratic and gradient modes when strongly aqueous solutions are injected, offering an attractive approach to increase loadability, while preserving peak shapes in preparative HILIC.

The peak distortion observed in hydrophilic interaction chromatography (HILIC) may be caused by the sample diluent to mobile phase mismatch. The United States Pharmacopeia (USP) method for organic impurities in cetirizine HCl tablets calls for such a mismatch, having a higher concentration of strong solvent in the sample diluent than in the mobile phase. A significant peak deformation is reported for cetirizine (a second-generation antihistamine) when it is purified on a Ethylene Bridged Hybrid (BEH) HILIC column (4.6mm×100mm, 2.5μm particles) using an acetonitrile-water eluent mixture and a sample diluent containing 7% and 9% water (in volume), respectively. The mechanism and physical origin of such peak distortion are related to (1) the diluent-to-eluent excess of water that propagates along the column at a velocity similar to that of the analyte, (2) the significant drop of the Henry's constant of the analyte upon increasing water concentration in the eluent, (3) the sample volume injected, and (4) to the pre-column sample dilution factor that depends on the characteristics of the LC instrument used. This proposed mechanism is validated from the calculation of the concentration profiles of cetirizine and water by using the equilibrium-dispersive (ED) model of chromatography. The observed distortion of cetirizine peaks is successfully predicted from the measurement of (1) the excess adsorption isotherm of water from acetonitrile onto the BEH HILIC adsorbent, (2) the retention factor of cetirizine as a function of the volume fraction (7, 8, and 9%) of water in the mobile phase, and (3) of the pre-column sample dispersion related to the instrument used (HPLC or UHPLC). The results of the calculations enables the user to anticipate the impacts of the diluent-to-eluent mismatch in water content, the injection volume, the analyte retention under infinite dilution, and of the pre-column sample dispersion on the amplitude of peak distortion in HILIC. Appropriate and permitted alterations of the USP method are then suggested based on a sound physico-chemical approach.

A hydrophilic interaction (HILIC) ultra-high performance liquid chromatography (UHPLC) with triple quadrupole tandem mass spectrometry (MS/MS) method was developed and validated for the quantification of 21 free amino acids (AAs). Compared to published reports, our method renders collectively improved sensitivity with lower limit of quantification (LLOQ) at 0.5~42.19 ng/mL with 0.3 μL injection volume (or equivalently 0.15~12.6 pg injected on column), robust linear range from LLOQ up to 3521~5720 ng/mL (or 1056 ~ 1716 pg on column) and a high throughput with total time of 6 min per sample, as well as easier experimental setup, less maintenance and higher adaptation flexibility. Ammonium formate in the mobile phase, though commonly used in HILIC, was found unnecessary in our experimental setup, and its removal from mobile phase was key for significant improvement in sensitivity (4~74 times higher than with 5 mM ammonium formate). Addition of 10 (or up to100 mM) hydrochloric acid (HCl) in the sample diluent was crucial to keep response linearity for basic amino acids of histidine, lysine and arginine. Different HCl concentration (10~100 mM) in sample diluent also excreted an effect on detection sensitivity, and it is of importance to keep the final prepared sample and calibrators in the same HCl level. Leucine and isoleucine were distinguished using different transitions. Validated at seven concentration levels, accuracy was bound within 75~125%, matrix effect generally within 90~110%, and precision error mostly below 2.5%. Using this newly developed method, the free amino acids were then quantified in a total of 544 African indigenous vegetables (AIVs) samples from African nightshades (AN), Ethiopian mustards (EM), amaranths (AM) and spider plants (SP), comprising a total of 8 identified species and 43 accessions, cultivated and harvested in USA, Kenya and Tanzania over several years, 2013~2018. The AN, EM, AM and SP were distinguished based on free AAs profile using machine learning methods (ML) including principle component analysis, discriminant analysis, naive Bayes, elastic net-regularized logistic regression, random forest and support vector machine, with prediction accuracy achieved at ca. 83~97% on the test set (train/test ratio at 7/3). An interactive ML platform was constructed using R Shiny at https://boyuan.shinyapps.io/AIV_Classifier/ for modeling train-test simulation and category prediction of unknown AIV sample(s). This new method presents a robust and rapid approach to quantifying free amino acids in plants for use in evaluating plants, biofortification, botanical authentication, safety, adulteration and with applications to nutrition, health and food product development.

An accurate, sensitive and selective analytical method is proposed for sulfonamide residues analysis in infant formulas based on hydrophilic interaction liquid chromatography (HILIC) and quadrupole time-of-flight mass spectrometry in full scan mode. The sample preparation approach involves low-temperature lipid precipitation followed by dispersive solid-phase extraction with PSA and C18 sorbents, which was successfully optimized using Plackett-Burman design. In order to achieve high analytical sensitivity, the influence of HILIC conditions on sulfonamide ionization was investigated, such as the mobile phase composition, buffer concentration, and sample diluent for injection. The method performance characteristics, including linearity (range 5–120 µg kg–1), reliable limits of quantification (between 5 and 20 µg kg–1), recovery (72.9–109.2%) and precision (coefficient of variation values ≤ 19.8%) under repeatability and within-laboratory reproducibility conditions, were in accordance with the Codex Alimentarius Commission CAC/GL 71–2009 for quantitative analytical methods for veterinary drug residues in foods. Moreover, adequate identification of the compounds was provided with accurate mass measurement of both precursor and fragment ions in one single run. Finally, the developed method was applied to thirty-five powdered milk-based infant formula samples available in the Brazilian market.

The mismatch of elution strength between the sample diluent and the eluent causes undesirable peak deformations for large sample volumes in gradient liquid chromatography. The solution to that problem consists in diluting the sample solution in a weak solvent. But the minimum dilution factor has to be determined by the user given some performance objectives. In silico approaches are applied in this work to find such adequate dilution factors. Two calculations methods are proposed for the prediction of peak distortions. The first comprehensive method is based on solving numerically the mass balance equations for all the analytes and the strong solvent. An excellent agreement between the experimental and the calculated gradient chromatograms is observed (sample diluent: acetonitrile/water, 50/50, v/v; injection volume: 15 μL; linear gradient: 5%–95% acetonitrile during 3 min) for five compounds (acetanilide, coumarin, benzoin, bi-naphthol, and dibutylphthalate) injected into a 2.1 × 50 mm column packed with 1.7 μm XBridge-C18 particles. This first method happens to be highly time-consuming and impractical for common users. Experimental work and calculation times are then minimized by applying a second method based on the basics of retention and dispersion of injected pulses. Despite being less accurate than the first method, the agreement between the experimental and calculated peak width remains physically meaningful allowing the experimenter to rapidly guess the required sample dilution factor for any combination of injected volume and strong solvent concentration in the sample solution.

Recent studies showed that injection of large volume of hydrophobic solvents used as sample diluents could be applied in reversed-phase liquid chromatography (RP-LC). This study reports a systematic research focused on the influence of a series of aliphatic alcohols (from methanol to 1-octanol) on the retention process in RP-LC, when large volumes of sample are injected on the column. Several model analytes with low hydrophobic character were studied by RP-LC process, for mobile phases containing methanol or acetonitrile as organic modifiers in different proportions with aqueous component. It was found that starting with 1-butanol, the aliphatic alcohols can be used as sample solvents and they can be injected in high volumes, but they may influence the retention factor and peak shape of the dissolved solutes. The dependence of the retention factor of the studied analytes on the injection volume of these alcohols is linear, with a decrease of its value as the sample volume is increased. The retention process in case of injecting up to 200μL of upper alcohols is dependent also on the content of the organic modifier (methanol or acetonitrile) in mobile phase.

Commercially available protein reference standard materials are widely used for the quantitation of intact proteins in biopharmaceuticals, food, and consumer products. However, the purity of protein reference standard materials are often assumed to be 100% or they may be assigned an inaccurate value because the methods used to determine protein purity often lack specificity and accuracy. In this study, a high performance liquid chromatography system equipped with a charged aerosol detector (HPLC-CAD) was used for universal response detection to provide a practical, specific, accurate, and robust method for the determination of the purity of protein reference standard materials. This work demonstrates the near uniform CAD responses for six proteins with different molecular weights and different structures. Flow injection analysis (FIA) was used to compare protein responses under various mobile phase and diluent compositions. Similar CAD responses for all six proteins were observed when the mobile phase composition included trifluoroacetic acid (TFA) and acetonitrile. These are typical conditions regularly applied to the separation of proteins by reversed phase (RP) chromatography. The universal response feature of the CAD was employed to determine the purity of Bowman-Birk inhibitor (BBI) reference standard material. This protein is an important ingredient in soybean products and has various therapy applications. Three major components were observed in the commercially available reference standard material by reversed phase gradient HPLC, BBI-Native, BBI-Isoform 1, and BBI-Isoform 2 at relative compositions of 60.0%, 34.2%, and 5.8%, respectively.

In this work, the simple analytical method for the determination of four fluoroquinolone antibiotics: ciprofloxacin, enrofloxacin, norfloxacin and danofloxacin, in environmental surface water samples is described. Sample pretreatment step was performed by the application of a technique based on supported liquid membrane extraction with the configuration of single hollow fiber (HF-SLM). The HPLC system with diode array detection was used for final analysis of studied analytes. Various parameters affecting the extraction efficiency during HF-SLM enrichment, such as type of membrane diluent, pH of donor (sample) and acceptor phases, as well as an enrichment time and salt content of sample were studied. Using the presented hollow-fiber extraction high recovery (70–80%) was achieved. It gave enrichment factor above 100. The detection limits in surface water samples, for the four target antibiotics, were at range 0.01–0.02 μg/l, when 10 ml samples were processed. The obtained results demonstrate the applicability of presented method for the selective extraction of fluoroquinolones in environmental water samples at ultratrace level. Errors, expressed as relative standard deviation (RSD) were below 8%, for all tested concentration levels.

The primary standard test method used for the determination of gasoline diluent in used engine oils is method D 3525-93 of the American Society for Testing and Materials (ASTM), which involves direct injection of used oil onto a packed GC column and flame ionization detection. Recently, we have utilized a new headspace sampling method: headspace solvent microextraction (HSM), for GC and GC-MS analysis of gasoline diluent in used engine oils. High resolution capillary columns can be used without the necessity for the use of inlet cryogenic cooling or expensive sampling interfaces. This analytical method, which we generically refer to as headspace microdrop analysis yields results comparable to those obtained using the ASTM method, with the added benefit that it allows the quantification of individual volatile diluent components, including benzene, toluene, ethylbenzene and the xylenes.

The rapid and simple determination of fatty vitamins (vitamins A and E) in serum by high-performance liquid chromatography with a column-switching technique was investigated. The dilution of serum with an aqueous solution containing surfactant and organic solvent and the use of an aqueous solution with organic solvent as a sample pretreatment were an effective means of improving the sample recovery. To prevent sample decomposition during storage, the addition of an antioxidant reagent into the diluent was required. Under the optimal conditions, the relative standard deviation (R.S.D.) values against the standard samples were 1.12% (16.7 I.U./dl), 0.25% (333 I.U./dl) for vitamin A, and 1.02% (0.43 microgram/ml), 0.45% (8.5 micrograms/ml) for vitamin E, respectively. The relative coefficients (r2) between the sample amounts in serum and the peak areas were 1.0000 in the range from 16.7 to 667 I.U./dl (for vitamin A) and 0.9998 from 0.434 to 17.46 micrograms/ml (for vitamin E). The recoveries of vitamins from spiked serums were ca. 100% (vitamin A) and ca. 86% (vitamin E), respectively. By the combination of an on-line deproteination column and diluting solution, the simple and rapid determination of fatty vitamins could be routinely achieved in 18-min intervals.

An improved high-performance liquid chromatographic (HPLC) method for the determination of pilocarpine, isopilocarpine, pilocarpic acid and isopilocarpic acid in ophthalamic solutions was developed. The new method was adapted from the USP HPLC method for pilocarpine base and has been shown to give superior resolution of pilocarpine related substances compared to any previously reported HPLC technique. However, evaluation of several brands of C 18 (octadecylsilane, ODS) columns revealed significant column-to-column variability: only to (YMC Pack ODS-AM and Supelco LC-18-DB) out of eight columns tested were capable of baseline resolution of these analytes. Additionally, optimization of the diluent was needed to prevent any significant interconversion of the carpic acids to their respective carpines. Analyses for pilocarpine and its degradation products in several commercial ophthalmic formulations were performed to demonstrate the precision, accuracy and general applicability of the method. The preparation of a stable resolution test solution is also described.

Monodisperse styrene-divinylbenzene gel beads in the range of 4.1–7.5 μm were prepared via a single-step swelling and polymerization method. The seed particles prepared by dispersion polymerization exhibited good absorption of the monomer phase. The resulting gel beads were evaluated as packing materials for gel permeation chromatographic columns. The pressure resistance of gel beads prepared with a volume ratio of diluent to monomers of unity was higher than 120 kg/cm2, and it decreased with the relative amount of diluent. The pore size tended to decrease with decrease in the swelling ratio of the seed polymer. The median pore size in a swollen state was controllable in the range 30–550 A.

Spherical polymer adsorbents for endotoxin adsorption were prepared by suspension copolymerization of N,N-dimethylaminopropylacrylamide (DMAPAA) with N-allylacrylamide (AAA). The amino-group contents and the pore size of the adsorbents were easily adjusted by changing the monomer ratio and diluent ratio. The more amino groups are introduced, the larger is the endotoxin-adsorbing capacity of the adsorbent, and the smaller the pore size (molecular mass exclusion, Mlim) of the adsorbent, the less acidic proteins such as bovine serum albumin are adsorbed. When Mlim was smaller than 300 (as the molecular mass of polysaccharide) and the amino group content was 4.5 mequiv. /g, the DMAPAA-AAA adsorbent showed a high endotoxin-removing activity at an ionic strength of μ = 0.05-0.4 and pH 5–9. The adsorbent was also able to remove endotoxin from a protein solution, naturally contaminated with endotoxin, at μ = 0.05 without affecting the recovery of the protein. The adsorbent can be completely regenerated by washing with 0.2 M sodium hydroxide followed by 2.0 M sodium chloride.

Column packings comprising an active solid sorbent diluted with an appropriately chosen inert, diluent solid have extremely desirable chromatographic characteristics. Theoretical plate heights can be substantially reduced in gas—solid chromatography (GSC) and at least maintained in gas—solid—liquid chromatography (GSLC) or high-performance liquid chromatography. Of greater importance, total analysis times can be reduced to any desired extent without loss of efficiency, and often with gain. Reduced analysis time can be traded-off for operation at lower temperature, a valuable option where samples are thermally labile or subject to catalytic reaction. Examples of difficult C1C4 aliphatic hydrocarbon analyses, both by GSC and GSLC, are given and it is concluded that the inert dilution technique provides a viable route to the extension of these modes of chromatography to a wider range of sample types than is currently common.

Porous spheres with average diameters of 5–300 μm have been prepared for the first time from poly(γ-methyl or γ-benzyl l -glutamate) alone, and their gel permeation chromatographic properties, both without further modification and after cross-linking with appropriate agents, have been examined. The polypeptide spheres were prepared by gradually removing the solvent from the suspension particles containing polypeptide. The particle size and porosity were controlled with ease by adjusting the viscosity of the peptide solution and suspension medium, and by selecting additional diluents in the sphering (solidification) process, respectively. The spheres of poly(γ-methyl l -glutamate) can not only withstand a remarkably high flow-rate, but also show typical gel permeation chromatographic behaviours in both aqueous and organic systems. These good properties are attributable to inter- and intramolecular hydrogen bonding based on the formation of specific polypeptide conformations.

To improve the resolution of a given sample mixture in liquid-solid chromatography, the characteristics of various components in the mobile phase were determined with a mixture of closely related compounds associated with DNA oligomer synthesis. Water (S0) was added so as to reduce peak tailing efficiently, but in amounts that would not significantly diminish retentivity in the silica gel column. The role of the stronger solvents, such as 1-propanol (S1) and dioxane (S2), in n-hexane (W) as diluent was quantitatively evaluated to control the retentivity. A linear correlation was found between the logarithms of the capacity ratios and molar concentration of the stronger component in the ternary solvent mobile phase. The selectivity of two stronger solvents was incorporated into the phase system to increase the resolution function for four given samples. A quaternary solvent system (W + S1 + S2 + S0) was prepared by integrating the characteristics of all the components, as determined by regression analysis. The multi-component phase system led to a high degree of resolution. This effective procedure was found suitable for analytical and preparative purposes in the resolution of various complex mixtures.

The linear relationship between the logarithmic values of capacity ratio and the molar fraction of one or two stronger solvents (S or S 1 + S 2 ) in ternary eluent systems containing two or one diluents, respectively (S + W 1 + W 2 or S 1 + S 2 + W), was determined by using steroid sapogenins as solutes in silica gel liquid-solid chromatography. The linear relationship was found to be reliable for concentrations of the S component as high as 100%. On the basis of this, an optimization procedure was established for a pair of model compounds in a ternary eluent by employing the retention-eluent composition correlation in two corresponding binary solvent systems.

Based on the previously reported linear relationship between the logarithm of the capacity factor and the logarithm of the binary solvent composition, a procedure for finding concentrations of a stronger eluent or a diluent in the binary mobile phase with an approximately equal elution strength for general compounds was established using mono- and disubstituted steroid derivatives as solutes on a silica get column. The design of an equi-eluotropic binary solvent system was compared with Snyder's and Neher's previously proposed calculations. This new procedure can be useful for the selection of an optimal solvent system that has maximal selectivity for a given sample mixture in liquid—solid chromatography.

Summary The extraction of Ni 2+ from aqueous solutions using Lix 64N solutions in various inert diluents has been studied and the optimum extraction conditions ascertained. The organic phase loaded with NiZ+ is passed through a column of a cationic resin (H + ), which contains only the water taken up on swelling. The effect of the pH of the aqueous film surrounding the resin grains on the capacity of Vionit CS-3 (−SO 3 H), CM-14 (−SH) and CC-1 (−COON) has been established. The loading curves of these resins have been drawn, at the optimum pH of the aqueous film, and the resin capacities shown to increase in the order −COOH 3 H. The effects of the diluent and of the flow-rate on the loading of the mercaptan resins, and the optimum elution conditions with HCl solution, have also been determined. A mechanism for the ion-exchange process is proposed.

The effects of mobile phase components on peak tailing and selectivity are examined for polar multi-functional solutes in liquid—solid chromatography on a silica gel adsorbent using various deoxynucleoside derivatives as sample solutes. Methanol is effective for suppressing peak tailing when combined with n-hexane as a diluent, but causes a decrease in the separation factor for pairs of deoxynucleoside derivatives. A combination of solvents is suggested for the diluent that will give an appropriate modification in separation factor so as to achieve maximum resolution of mixtures of polar multi-functional compounds.

Gas chromatography is useful for the analysis of the complexing agent (tributyl phosphate) and the diluent (hyfrane) which constitute the extraction solvents used in nuclear fuel reprocessing plants. Analyses were carried out to determine the composition of the solvents at different points in the extraction circuit, and the tributyl phosphate content of the plant waste products.

A thin-layer chromatographic method is described for the detection of four types of petroleum oils used as diluents in creosote. These oils vary widely in aromatic and paraffinic content. The presence of these oils can be demonstrated down to a level of 0.25% in creosote. The indicator, α-cyclodextrin followed by iodine fumes, should be useful in other applications where differentiation between aromatic compounds and hydrocarbons is desired.

A continuation is presented of an investigation of the chromatographic behavior of metallic nitrates in tri-nbutyl phosphate. Experiments were carried out varying the technique, the initial concentration of the nitrates and, or the nitric acid, the organic diluent. and the concentration of TBP in the organic diluent. In solutions containing 0 to 5% TBP all ions had R/sub F/ values equal to zero. An increase of TBP above 20% caused R/sub F/ values to increase slightly. No other organic diluents used showed any great advantages over purified kerosene, B.P. 210 to 250 deg . For variations of acid concentration, 1 to 16 M, the R/sub F/ values of most ions are not affected. (B.O.G.)