Chromatographic determination of copper speciation in jet fuel.

A method is described that allows one to distinguish and quantitate two different classes of copper compounds in the same hydrocarbon sample. This will enable the study of the effects of different copper compounds on the performance and stability of petroleum samples. Copper N,N'-disalicylidene-1,2-propylenediamine (CuDMD) and several copper carboxylates were preconcentrated from a hydrocarbon matrix using a column packed with polyvinylpyrrolidone, (C(6)H(9)NO)(x), a novel polymeric stationary phase. The copper complexes were then sequentially eluted using a step gradient program beginning with hexane/isopropyl alcohol as the eluent and ending with an acetic acid/isopropyl alcohol eluent. The copper complexes were detected by serial UV absorbance and flame atomic absorbance (FAA) detection. With on-column preconcentration and FAA detection, the limits of detection were 7 and 40 ppb copper for CuDMD and the copper carboxylates respectively. With this method, it was possible to distinguish between the two different classes of copper compounds in the same hydrocarbon sample, which will help to provide an understanding of the catalytic activity of different copper compounds, leading to a better understanding of the factors causing fuel instability. The method promises to be a valuable tool in the analysis and characterization of copper compounds in petroleum samples.

High-speed chromatographic analysis of high-fructose corn syrup for process monitoring.

High-speed chromatography is coupled with numerical methods for analyzing unresolved chromatograms and applied to a process analysis of high-fructose corn syrup. A column selection process is demonstrated where a minimum amount of resolution is sacrificed in order to decrease analysis time from over 5 min to 25 sec. Two data analysis methods, linear least squares regression and the sequential chromatogram ratio technique coupled with sequential suppression, are compared for their ability to quantitate the poorly resolved chromatograms. Both methods fit pure component analyte chromatograms, collected on a computer, to a sample chromatogram with unknown concentrations of each analyte. For a high-fructose corn syrup sample with a nominal fructose concentration of 55%, linear least squares analysis gave a fructose concentration percentage of 57.2 +/- 0.9%. The sequential chromatogram ratio algorithm gave a fructose concentration percentage of 57.9 +/- 0.7%.

Isocratic mixed mode liquid chromatographic separation of phospholipids with octadecylsilane-silica stationary phases.

Molecular species of phosphatidylcholine, phosphatidylethanolamine and phosphatadic acid were resolved by isocratic reversed phase high performance liquid chromatography (HPLC) using mobile phases of methanol-isopropanol containing para-toluenesulfonic acid (p-tsa). Separation by both non-polar fatty acid chain length and by polar head group functionality was achieved concurrently upon a commercially available octadecylsilane (C18) column endcapped with trimethylsilane (C1) groups. Using a mobile phase of 97.5:2.5 methanol:isopropanol with 7OmMpara-toluenesulfonic acid (p-tsa) at a pH of approximately 1, twelve phospholipid species comprised of four tail group classes (dilauroyl-,dimyristoyl-, dipamitoyl- and distearoyl-) and three head group speciations (phosphatidylcholine, phosphatidylethanolamine and phosphatadic acid) were separated. The column was then exposed to the acidic mobile phase for 48 hours continuously during which the bound phase underwent severe acid-induced hydrolysis, after which the separation of the twelve analytes resulted in the separation of the phospholipid species by non-polar tail group alone. The experimental results are discussed in terms of potential separation mechanisms including dependency of the separation on adsorption of the counter ion into the stationary phase, residual acidic silanol group interactions, and potential interactions of the surface active phospholipids with C1 groups.

Enhanced surfactant determination by ion-pair formation using flow-injection analysis and dynamic surface tension detection.

Chemical analysis of surface active species (surfactants) is of interest for many applications, such as in process monitoring, biomedical applications, environmental monitoring and surface science investigations. Recently, we reported a dynamic surface tension detector (DSTD) based upon optically probing the size of a repeating drop resulting from constant flow of an aqueous solvent out of the end of a capillary. Presence of a surfactant in a growing drop reduces the surface tension at the air-solvent interface, causing the drop to detach at a smaller volume, which is detected. The DSTD has a kinetic dependence, and with increasing flow rate the sensitivity decreases due to diffusional and adsorption effects. We report that for the sodium salt of dodecylsulfate (DS), the DSTD performs significantly better with a stainless steel (S.S.) capillary dropper than with a fused silica dropper because the S.S. dropper exhibits a smaller adsorption effect as a function of time. Flow-injection analysis with the DSTD of DS was found to enhance sensitivity 50-fold by in-situ reaction with the ion-pair reagent tetrabutylammonium hydroxide (TBA) in water, even though the TBA alone was not very surface active. The TBA-DS system serves as a model for a selective detection method in which surface activity is exploited and enhanced. The detection limit for DS, as TBA-DS, was 400 ppb. Additionally, weakly surface active species such as TBA could be analyzed "indirectly" by ion-pair formation with DS. The enhanced sensitivity is due to increased packing of the ion-pairs at the air-aqueous solvent interface. The flow rate dependence on the sensitivity of detecting the TBA-DS ion-pair was examined. Two limiting conditions were observed as a function of ion-pair concentration: sensitivity decreases linearly with inverse flow rate at high flow rates and approaches a steady state at slower flow rates.

Gas chromatographic sensing on an optical fiber by mode-filtered light detection.

A chemical sensor for gas phase measurements is reported which combines the principles of chemical separation and fiber optic detection. The analyzer incorporates an annular column Chromatographic sensor, constructed by inserting a polymer-clad optical fiber into a silica capillary. Light from a helium-neon laser is launched down the fiber, producing a steady intensity distribution within the fiber, but a low background of scattered light. When sample vapor is introduced to the sensor, and an analyte-rich volume interacts with the polymer cladding, Chromatographic retention is observed simultaneously with a change in the local refractive index of the cladding. An increase in cladding refractive index (RI) causes light to be coupled out of the fiber, with detection at a right-angle to the annular column length to provide optimum S/N ratio. This detection mechanism is called mode-filtered light detection. We report a gas Chromatographic separation on a 3.1 m annular column (320 microm i.d. silica tube, 228 microm o.d. fiber with a 12 microm fluorinated silicone clad) of methane, benzene, butanone and chlorobenzene in 6 min. The annular column length was reduced to 22 cm to function as a sensor, with selected organic vapors exhibiting unique retention times and detection selectivity. The detection selectivity is determined by the analyte RI and the partition coefficient into the cladding. The calculated limit of detection (LOD) for benzene vapor is 0.03% by volume in nitrogen, and several chlorinated species had LOD values less than 1%. For binary mixtures of organic vapors, the detected response appears to be the linear combination of the two organic standards, suggesting that the annular column may be useful as a general approach for designing chemical sensors that incorporate separation and optical detection principles simultaneously.

Novel calibration of a dynamic surface tension detector: flow injection analysis of kinetically-hindered surface active analytes.

First, a novel technique for calibration of a dynamic surface tension detector (DSTD) is described. The DSTD measures the differential pressure as a function of time across the liquid-air interface of growing drops that repeatedly form and detach at the end of a capillary tip. The calibration technique utilizes the ratio of pressure signals acquired from the drop growth of two separate solutions, i.e. a standard solution and a corresponding mobile phase, such as water, both of which have a known surface tension. Once calibrated, the dynamic surface tension of an analyte is obtained from the ratio of the pressure signals from the analyte solution to that of the mobile phase solution. Thus, this calibration technique eliminates the need to optically image the radius of the expanding drop of liquid. Accurate dynamic surface tension determinations were achieved for aqueous sodium dodecyl sulfate (SDS) solutions over a concentration range of 0.5-5.4 mM. The measured surface tensions for these SDS solutions range from 70.3 to 46.8 dyne/cm and were in excellent agreement with the literature. A precision of 0.2 dyne/cm (1 S.D.) was routinely obtained. Second, the DSTD with this calibration technique was combined with flow injection analysis (FIA) for the study of model protein solutions and polymer solutions. The kinetic surface tension behavior of aqueous bovine serum albumin (BSA) solutions as a function of concentration and flow rate is presented. Evaluation of the dynamic surface tension data illustrates that a protein such as BSA initially exhibits kinetically-hindered surface tension lowering, i.e. a time dependence, as BSA interacts with the liquid-air interface of an expanding drop. FIA/DSTD is then shown to be an effective tool for the rapid study of kinetically-hindered surfactant mixtures. It was found that mixtures of SDS and the polymeric surfactant Brij(R)-35 (lauryl polyoxyethylene ether with an average molecular weight of 1200 g/mol) result in essentially an additive lowering of the surface tension. Mixtures of polyethylene glycol (PEG), with an average molecular weight of 1470 g/mol, and Brij(R)-35, however, result in a competitive (non-additive) surface tension with the Brij(R)-35 dominating the response.

Reversed phase liquid chromatography with UV absorbance and flame ionization detection using a water mobile phase and a cyano propyl stationary phase Analysis of alcohols and chlorinated hydrocarbons.

The development of liquid chromatography with a commercially available cyano propyl stationary phase and a 100% water mobile phase is reported. Separations were performed at ambient temperature, simplifying instrumental requirements. Excellent separation efficiency using a water mobile phase was achieved, for example N=18 800, or 75 200 m(-1), was obtained for resorcinol, at a retention factor of k'=4.88 (retention time of 9.55 min at 1 ml min(-1) for a 25 cmx4.6 mm i.d. column, packed with 5 mum diameter particles with the cyano propyl stationary phase). A separation via reversed phase liquid chromatography (RP-LC) with a 100% water mobile phase of six phenols and related compounds was compared to a separation of the same compounds by traditional RP-LC, using octadecylsilane (ODS), i.e. C18, bound to silica and an aqueous mobile phase modified with acetonitrile. Nearly identical analysis time was achieved for the separation of six phenols and related compounds using the cyano propyl stationary phase with a 100% water mobile phase, as compared to traditional RP-LC requiring a relatively large fraction of organic solvent modifier in the mobile phase (25% acetonitrile:75% water). Additional understanding of the retention mechanism with the 100% water mobile phase was obtained by relating measured retention factors of aliphatic alcohols, phenols and related compounds, and chlorinated hydrocarbons to their octanol:water partition coefficients. The retention mechanism is found to be consistent with a RP-LC mechanism coupled with an additional retention effect due to residual hydroxyl groups on the cyano propyl stationary phase. Advantages due to a 100% water mobile phase for the chemical analysis of alcohol mixtures and chlorinated hydrocarbons are reported. By placing an absorbance detector in-series and preceding a novel drop interface to a flame ionization detector (FID), selective detection of a separated mixture of phenols and related compounds and aliphatic alcohols is achieved. The compound class of aliphatic alcohols is selectively and sensitively detected by the drop interface/FID, and the phenols and related compounds are selectively and sensitively detected by absorbance detection at 200 nm. The separation and detection of chlorinated hydrocarbons in a water sample matrix further illustrated the advantages of this methodology. The sensitivity and selectivity of the FID signal for the chlorinated hydrocarbons are significantly better than absorbance detection, even at 200 nm. This methodology is well suited to continuous and automated monitoring of water samples. The applicability of samples initially in an organic solvent matrix is explored, since an organic sample matrix may effect retention and efficiency. Separations in acetonitrile and isopropyl alcohol sample matrices compared well to separations with a water sample matrix.

Bonded stationary phases for reversed phase liquid chromatography with a water mobile phase: application to subcritical water extraction.

Reversed phase high-performance liquid chromatography (RP-HPLC) is demonstrated for hydrophobic analytes such as aromatic hydrocarbons on a chemically bonded stationary phase and a mobile phase consisting of only water. Reversed phase liquid chromatography separations using a water-only mobile phase has been termed WRP-LC for water-only reversed phase LC. Reasonable capacity factors are achieved through the use of a non-porous silica substrate resulting in a chromatographic phase volume ratio much lower than usually found in RP-HPLC. Two types of bonded WRP-LC columns have been developed and applied. A brush phase was synthesized from an organochlorosilane. The other phase, synthesized from an organodichlorosilane, is termed a branch phase and results in a polymeric structure of greater thickness than the brush phase. A baseline separation of a mixture containing benzaldehyde, benzene, toluene, and ethyl benzene in less than 5 min is demonstrated using a water mobile phase with 12 000 plates generated for the unretained benzaldehyde peak. The theoretically predicted minimum reduced plate height is also shown to be approached for the unretained analyte using the brush phase. As an application, subcritical water extraction (SWE) at 200 degrees C is combined with WRP-LC. This combination allows for the extraction of organic compounds from solid matrices immediately followed by liquid chromatographic separation of those extracted compounds all using a solvent of 100% water. We demonstrate SWE/WRP-LC by spiking benzene, ethyl benzene, and naphthalene onto sand then extracting the analytes with SWE followed by chromatographic separation on a WRP column. A sand sample contaminated with gasoline was also analyzed using SWE/WRP-LC. This extraction process also provides kinetic information about the rate of analyte extraction from the sand matrix. Under the conditions employed, analytes were extracted at different rates, providing additional selectivity in addition to the WRP-LC separation.

Microbore liquid chromatography and refractive index gradient detection of low-nanogram and low-ppm quantities of carbohydrates.

A refractive index gradient detector is presented as a universal detector in the microbore high-performance liquid chromatography analysis of carbohydrates. Simultaneously, low-ng and low-ppm injected quantities of carbohydrates were detected at the 3 x root-mean-square baseline noise level. A typical microbore high-performance liquid chromatography chromatogram separating fructose from sucrose followed by refractive index gradient (RIG) detection is reported. Use of a position sensitive detector (PSD) in the RIG detector design is reported and experimental considerations discussed. Optimization of the PSD-based RIG detector is addressed. Potential for the device in industrial and clinical applications is considered.

Review of analytical measurements facilitated by drop formation technology.

The use of drops in chemical analysis methodology and instrumentation has a deeply rooted past in the area of electrochemistry through the evolution of the dropping mercury electrode (DME). This history has also been deeply rooted in the field of surface science due to the inextricable connection between surface tension forces and drop formation. While the use of the DME is well established, the evolution of drop-based analytical measurements using aqueous and/or organic drops is a rapidly emerging and diverse field, encompassing several interdisciplinary areas of science: surface science and interfacial surface tension phenomena, spectroscopic detection, analytical instrumentation hyphenation, liquid membrane separation, reagent chemistry, electrochemistry, and so on. This review of 112 references covers various aspects of drop-based analytical measurements involving aqueous and/or organic drops. The review is divided into four sections, although the classification of a particular reference into a given section can sometimes be argued. The first section considers the use of drops as a detector component. The second section deals with fundamental studies that probe drop-related chemical and physical phenomena that are relevant to current and future developments in analytical chemistry. The next section covers recent advances in the area of microfluidic sample handling and instrumentation hyphenation. The final section reports upon emerging technologies aimed toward drop-based chemical analyzers that incorporate a number of steps in a chemical analysis: microextraction, preconcentration, reagent chemistry, microfluidic handling, and detection.

Reversed phase liquid chromatography of organic hydrocarbons with water as the mobile phase.

Reversed phase high-performance liquid chromatography (RP-HPLC) is demonstrated for hydrophobic analytes such as aromatic hydrocarbons using only water as the mobile phase. Achievement of reasonable capacity factors for these types of compounds without the need for toxic and costly organic modifiers in the mobile phase is accomplished by substantially decreasing the phase volume ratio of stationary phase relative to the mobile phase volume and by increasing the polarity of the stationary phase relative to stationary phase materials commonly used for RP-HPLC. Applying a stationary phase of trifluoropropylsiloxane, which is a common gas chromatographic stationary phase material, to nonporous glass microspheres yields a stationary phase with a phase volume ratio reduced by about 2 orders of magnitude as compared to common liquid chromatographic packing materials. As a result, a separation was obtained for hydrophobic organic analytes such as benzene, toluene, ethylbenzene, and isopropylbenzene using a water mobile phase at ambient temperature. A separation of sodium benzoate, benzaldehyde, benzene, and butyrophenone is shown in less than 3 min using a water mobile phase and UV/visible absorbance detection. Additionally, the separation of the ionic surfactant species octyl sulfate and dodecyl sulfate in water in less than 3 min, using unsuppressed conductivity detection, is achieved with a separation mechanism based on interactions with the hydrophobic portion of the surfactant. A water mobile phase offers many potential advantages over traditional mixed aqueous/organic solvent systems. In addition to saving on the cost and expense of buying and disposing of toxic solvents and waste, there is less exposure of the operator to potentially harmful solvents. Increased consistency in reproducing retention times can be expected, since there will not be any variability in solvent strength due to slight variations in mobile phase composition. A water mobile phase produces an environment that should provide an inherent advantage of increased signal-to-noise ratio for detection. Additionally, excellent predictions of the octanol/water partitioning coefficient and aqueous solubility for hydrophobic analytes are obtained from a single measurement of the capacity factor in the water mobile phase.

Whole-column radioactivity detection: simultaneous separation and enhanced detectability.

The development of a whole-column radiation detector for measurement and separation of low amounts of beta emitting analytes is described. The design of this detector is unique with all of the chromatography media located within the detector volume. This whole-column design provides the advantage of increased radiation signal without loss of chromatographic efficiency, which translates to increased detectability. This increase was compared theoretically with flow-through radiation detection, and the theory was tested experimentally. Using two analytes, carbon-11-labeled m-hydroxyephedrine and alpha-methylepinephrine, only 3 and 8 Bq (80 and 220 pCi), respectively, were needed to obtain a 10% coefficient of variation using whole-column detection. For [11C]-m-hydroxyephedrine, 100 times more radioactivity was required to achieve the same coefficient of variation using flow-through detection. A limit of detection (LD) for the analytes of 2 Bq (54 pCi) was obtained for whole-column detection, an improvement of 50 in LD compared with flow-through detection. Signal improvement increased linearly with the chromatographic resolution. The whole-column detection method is robust and applicable to many chromatographic separations.

Increasing the number of analyzable peaks in comprehensive two-dimensional separations through chemometrics.

Comprehensive two-dimensional (2-D) separations are emerging as powerful tools for the analysis of complex samples. The substantially larger peak capacity for a given length of time relative to 1-D separations is a well-known benefit of comprehensive 2-D separation methods. Unfortunately, with complex samples, the probability of peak overlap in 2-D separations is still quite high. This is especially true if one desires to speed up the analysis by reducing the run time and, thus, by reducing the resolving power along the first dimension separation. Chemometric methods hold considerable promise to overcome the limitations brought upon by the likelihood of peak overlap. Thus, chemometric methods should be able to effectively extend the resolving power of 2-D separation methods. In this paper, the theoretical enhancement provided by application of the generalized rank annihilation method (GRAM) for the analysis of unresolved peaks in comprehensive 2-D separations is carefully modeled and critically evaluated. First, Monte Carlo simulations are used to determine the conditions where the use of GRAM results in the successful analysis of unresolved peaks. A wide range of experimental conditions and performance criteria are modeled, typical to many available 2-D separation methods, including analyte/interference peak height ratio, first- and second-dimension resolutions, signal-to noise ratio, injection volume reproducibility, and run-to-run retention time reproducibility. Essentially, a wide range of experimental conditions and performance criteria are found to provide reliable data amenable to GRAM analysis. The information gleaned from this first set of simulations is then used in conjunction with Monte Carlo simulations of comprehensive 2-D separations. For these simulated 2-D separations, the total number of analyzable peaks when using GRAM was determined and found to be substantially better than using only traditional quantitative methods such as peak integration or height. For example, it was determined that the use of GRAM increases the average number of analyzable peaks by a factor of 2 for 2-D separations in which the peak capacity is 67% occupied by randomly distributed peaks. The results of the studies are general, and the use of GRAM should increase the number of analyzable peaks for all forms of comprehensive 2-D separations.

Separation and determination of denatured caseins by hydrophobic interaction chromatography Part II. Method validation and applications.

A method recently described for the separation of denatured alpha-, beta- and kappa-caseins by hydrophobic interaction chromatography was validated by the analysis of reference skim milk powder (BCR-063R) certificated for total nitrogen content. The method is based on fast and easy solubilization of commercial and real samples by 4.0 M guanidine thiocyanate and elution on a TSK-Gel Phenyl-5PW column (TosoHaas) in the presence of 8.0 M urea in the mobile phase. No preliminary precipitation or separation of the casein fraction is required. A linear relationship between the concentration of casein and peak area (UV absorbance detector at 280 nm) was obtained over the concentration range 0.5-60 microM. The detection limits for alpha-, beta- and kappa-caseins ranged between 0.30 and 0.65 microM. The precision of the method was evaluated; the relative standard deviation for alpha-, beta- and kappa-casein determination ranged between 2.2 and 2.7% for standard solutions and between 3.5 and 6.2% for real sample solutions. The mean casein content found in 10 aliquots of BCR-063R calculated with respect to the total protein content (estimated on the basis of certified total nitrogen content) was 79.1+/-2.7%. Results of linear fitting of standard additions data for alpha-, beta- and kappa-caseins to BCR-063R were compared with linear fitting of alpha-, beta- and kappa-casein calibration data. The method was applied to commercial caseins and to 31 real, raw samples [processed cow's milk (pasteurised, UHT-treated), follow-up milk powders, cream, cheeses, casein-free infant formulae, cookies for babies containing milk proteins] with the aim of showing the wide applicability of the method in order to determine alpha-, beta- and kappa-caseins.

Objective data alignment and chemometric analysis of comprehensive two-dimensional separations with run-to-run peak shifting on both dimensions.

Data from comprehensive two-dimensional (2-D) separation techniques, such as comprehensive 2-D gas chromatography (GC x GC), liquid chromatography/liquid chromatography (LC x LC) and liquid chromatography/ capillary electrophoresis (LC x CE) can be readily analyzed by various chemometric methods to increase chemical analysis capabilities. A retention time alignment, preprocessing method is presented that objectively corrects for run-to-run retention time variations on both separation dimensions of comprehensive 2-D separations prior to application of chemometric data analysis algorithms. The 2-D alignment method corrects for run-to-run shifting of a sample data matrix relative to a standard data matrix on both separation time axes in an independent, stepwise fashion. After 2-D alignment, the generalized rank annihilation method (GRAM) is successfully applied, substantiating the performance of the alignment method. The alignment method should have important implications, because most 2-D separation techniques exhibit, in the context of chemometric data analysis, considerable run-to-run retention time shifting on both dimensions. Even when there are only three to four points/peak, that is, with three to four separations on the second dimension (column 2) per peak width from the first dimension (column 1), the 2-D alignment coupled with GRAM provides dependable analyte peak identification capabilities and adequate quantitative precision for unresolved analyte peaks. Thus, the 2-D alignment algorithm is applicable to lower data density conditions, which broadens the scope of chemometric analysis to high-speed 2-D separations.

Simultaneous flame ionization and absorbance detection of volatile and nonvolatile compounds by reversed-phase liquid chromatography with a water mobile phase.

A flame ionization detector (FID) is used to detect volatile organic compounds that have been separated by water-only reversed-phase liquid chromatography (WRP-LC). The mobile phase is 100% water at room temperature, without use of organic solvent modifiers. An interface between the LC and detector is presented, whereby a helium stream samples the vapor of volatile components from individual drops of the LC eluent, and the vapor-enriched gas stream is sent to the FID. The design of the drop headspace cell is simple because the water-only nature of the LC separation obviates the need to do any organic solvent removal prior to gas phase detection. Despite the absence of organic modifier, hydrophobic compounds can be separated in a reasonable time due to the low phase volume ratio of the WRP-LC columns. The drop headspace interface easily handles LC flows of 1 mL/min, and, in fact, compound detection limits are improved at faster liquid flow rates. The transfer efficiency of the headspace interface was estimated at 10% for toluene in water at 1 mL/min but varies depending on the volatility of each analyte. The detection system is linear over more than 5 orders of 1-butanol concentration in water and is able to detect sub-ppb amounts of o-xylene and other aromatic compounds in water. In order to analyze volatile and nonvolatile analytes simultaneously, the FID is coupled in series to a WRP-LC system with UV absorbance detection. WRP-LC improves UV absorbance detection limits because the absence of organic modifier allows the detector to be operated in the short-wavelength UV region, where analytes generally have significantly larger molar absorptivities. The selectivity the headspace interface provides for flame ionization detection of volatiles is demonstrated with a separation of 1-butanol, 1,1,2-trichloroethane (TCE), and chlorobenzene in a mixture of benzoic acid in water. Despite coelution of butanol and TCE with the benzoate anion, the nonvolatile benzoate anion does not appear in the FID signal, allowing the analytes of interest to be readily detected. The complementary selectivity of UV-visible absorbance detection and this implementation of flame ionization detection allows for the analysis of volatile and nonvolatile components of complex samples using WRP-LC without the requirement that all the components of interest be fully resolved, thus simplifying the sample preparation and chromatographic requirements. This instrument should be applicable to routine automated water monitoring, in which repetitive injection of water samples onto a gas chromatograph is not recommended.

Two-dimensional gas chromatography and trilinear partial least squares for the quantitative analysis of aromatic and naphthene content in naphtha.

Quantitative analysis of naphtha samples is demonstrated using comprehensive two-dimensional gas chromatography (GC x GC) and chemometrics. This work is aimed at providing a GC system for the quantitative and qualitative analysis of complex process streams for process monitoring and control. The high-speed GC x GC analysis of naphtha is accomplished through short GC columns, high carrier gas velocities, and partial chromatographic peak resolution followed by multivariate quantitative analysis. Six min GC x GC separations are analyzed with trilinear partial least squares (tri-PLS) to predict the aromatic and naphthene (cycloalkanes) content of naphtha samples. The 6-min GC x GC separation time is over 16 times faster than a single-GC-column standard method in which a single-column separation resolves the aromatic and naphthene compounds in naphtha and predicts the aromatic and naphthene percent concentrations through addition of the resolved signals. Acceptable quantitative precision is provided by GC x GC/tri-PLS.

High speed liquid chromatography of phenylethanolamines for the kinetic analysis of [11C]-meta-hydroxyephedrine and metabolites in plasma.

A method is developed and described for analysis of [11C]-meta-hydroxyephedrine, [11C]MHED, a tracer of cardiac function, and its metabolites in plasma samples. The method combines on-column solid-phase extraction and separation on a single weak cation-exchange column. Phenylethanolamines were used to develop the separation method that concentrates the analytes on-column from physiological saline and then elutes them by changing to an acidic mobile phase. Hydrophobic interactions determine the selectivity, and elution order is the same as for reversed-phase liquid chromatography on a C1 stationary phase. The mechanism of separation is mixed mode, with ion-exchange coupled with a reversed-phase liquid chromatography mechanism. Each sample analysis requires only 10 min and does not require deproteinization or the use of organic solvents. In human samples, a single plasma metabolite of [11C]MHED along with the parent compound were observed using this method. The method was sufficiently rapid so that in 70 min seven samples were assayed, providing a well-defined time course for MHED and its metabolites in blood. The metabolite concentration increased with time to approximately 85% of the plasma activity 50 min after administration. The results with the developed method are comparable to those described for reversed-phase separations, with the advantage that our method does not require deproteinization, reducing sample analysis time by a factor of two.

Cost-effective flow injection spectrophotometric assay of iron content in pharmaceutical preparations using salicylate reagent.

A new flow injection procedure for an assay of Fe(III) by using salicylate obtained from antipyretic powder, which is a cheap and easily available reagent, is proposed. A red complex was continuously monitored by a laboratory-made green LED colorimeter. A linear calibration was obtained in the range of 1-20mgFel(-1) with a detection limit of 0.5mgFel(-1) and R.S.D.s of 1.4-5.4% (n=3, for 1-20mgFel(-1)). The new procedure was applied to assay iron contents in pharmaceutical preparations. The results were in good agreement with those of the USP standard method.

A Raman waveguide detector for liquid chromatography.

A novel real-time liquid core Raman waveguide detector designed for liquid chromatographic applications is described. The Raman waveguide detector provides enhanced selectivity over typical high-performance liquid chromatography (HPLC) detectors. The waveguide detector also greatly improves the sensitivity of a typical Raman measurement without resorting to surface enhancement or resonance approaches and is compatible with the typical peak width volumes eluted by microbore and minibore HPLC (packed 1-2-mm-i.d. columns). Detection limit enhancements of over 1000-fold have been achieved for the measurement of alcohols in the aqueous phase with the Raman cell utilizing liquid core waveguide technology. The liquid core waveguides demonstrated in this study were constructed using Teflon AF 2400 tubing with a refractive index of 1.29. The low refractive index of the polymer material allowed HPLC separations with Raman detection to be performed with an aqueous mobile phase. A calibration curve for aqueous solutions of 2-propanol was generated and a limit of detection (LOD) of 2 ppm was determined. The Raman waveguide detector is demonstrated for the HPLC analysis of alcohol test mixtures, with LODs in the low-ppm range at the detector. By coupling the temporal separation achieved by HPLC with the vibrational information gleaned from Raman detection, an information-rich multivariate data matrix is obtained that can be deconvoluted to provide chemical speciation even when the HPLC resolution is poor. In this paper, we will discuss the physical and optical design of the Raman waveguide detector and the demonstration of the detector for HPLC detection.