High-performance liquid chromatographic method for the simultaneous measurement of floxuridine and fluorouracil in human body fluids.

A method for the simultaneous measurement of floxuridine (5-fluorodeoxyuridine) and fluorouracil in human plasma and peritoneal fluid has been developed. This method utilizes high-performance liquid chromatographic analysis with a Zorbax RX column (25 cm x 4.6 mm I.D.) plus a guard cartridge of the same material. The sensitivity limits for this assay are 0.25 mumol/l in a 20-microliters sample. The detection limit at a signal-to-noise ratio of 3 is 2.5 nmol/l. This procedure has been used to quantitatively measure concentration versus time profiles of floxuridine and fluorouracil in plasma and peritoneal fluid of human patients after receiving intraperitoneal administration of floxuridine.     

An electrochemical enrichment procedure for the determination of heavy metals by total-reflection X-ray fluorescence spectroscopy

An electrolytic separation and enrichment technique was developed for the determination of trace elements by total-reflection X-ray fluorescence spectroscopy (TXRF). The elements of interest are electrodeposited out of the sample solution onto a solid, polished disc of pure niobium which is used as sample carrier for the TXRF measurement. The electrochemical deposition leads to a high enrichment of the analytes and at the same time to a removal of the matrix. This results in substantially improved detection limits in the lower picogram per gram region. The deposited elements are directly measured by TXRF without any further sample preparation step. The homogeneous thin layer of the analytes is an ideal sample form for TXRF, because scattered radiation from the sample itself is minimized. The proposed sample preparation method is useful particularly for the analysis of heavy metals in liquid samples with for TXRF disturbing matrices, e.g. sea water.     

Use of a novel array detector for the direct analysis of solid samples by laser ablation inductively coupled plasma sector-field mass spectrometry

The use of laser ablation (LA) as a sample-introduction method for inductively coupled plasma mass spectrometry (ICP-MS) creates a powerful tool for trace elemental analysis. With this type of instrument, high analyte spatial resolution is possible in three dimensions with ng/g limits of detection and minimal sample consumption. Here, simultaneous detection is used to eliminate the correlated noise that plagues the ablation process. This benefit allows analyses to be performed with single laser pulses, resulting in improved depth resolution, even less sample consumption, and improved measurement precision. The new instrument includes an LA sample-introduction system coupled to an ICP ionization source and a Mattauch-Herzog mass spectrograph (MHMS) fitted with a novel array detector. With this instrument, absolute limits of detection are in the tens to hundreds of fg regime and isotope-ratio precision is better than 0.02% RSD with a one-hour integration period. Finally, depth-profile analysis has been performed with a depth resolution of 5 nm per ablation event.     

Continuous flow microextraction combined with high-performance liquid chromatography for the analysis of pesticides in natural waters

Continuous flow microextraction (CFME) combined with high-performance liquid chromatography-ultraviolet (HPLC-UV) detection has been applied to the analysis of five widely used pesticides, simazine, fensulfothion, etridiazole, mepronil and bensulide, present at trace levels in water samples. CFME employs a single organic solvent drop positioned at the tip of a polyether ether ketone (PEEK) tubing, which is immersed in a continuous flowing aqueous sample solution in a 0.5-ml glass chamber. The PEEK tubing acts as the organic drop holder and fluid delivery duct. Analytes are partitioned between the organic drop and the bulk sample solution. Important extraction factors including type of solvent, its volume, sample solution flow rate, extraction time, its pH and addition of salt were investigated. All pesticides exhibit good linearity in the investigated concentration range of 25-250 ng ml(-1) with coefficients of determination (R2) ranging from 0.9879 to 0.9999 under the optimized conditions. Detection limits lower than 4 ng ml(-1) were obtained for all analytes. The method was evaluated by analyzing natural water sample collected from a reservoir in Singapore. This study for the first time demonstrated the compatibility of CFME procedure and HPLC separation.     

Attogram detection limits using laser induced fluorescence

Laser induced fluorescence has produced outstanding detection limits in liquid phase analysis. This paper presents a general method for optimizing detection limits as a function of sample volume.     

Ionization suppression effects with condensed phase membrane introduction mass spectrometry: methods to increase the linear dynamic range and sensitivity

Condensed phase membrane introduction mass spectrometry (CP‐MIMS) is an online analytical method that allows for the direct, trace level measurement of a wide range of analytes in complex samples. The technique employs a semi‐permeable membrane that transfers analytes from a sample into a flowing acceptor solvent, which is directly infused to an atmospheric pressure ionization source, such as electrospray or atmospheric pressure chemical ionization. While CP‐MIMS and variants of the technique have been in the literature for nearly a decade, much of the work has focused on instrument development. Few studies have thoroughly addressed quantitative methods related to detection limits, ionization suppression, or linear dynamic range. We examine ionization suppression in the direct rapid quantitation of analytes by CP‐MIMS and introduce several analytical strategies to mitigate these effects, including the novel implementation of a continuously infused internal standard in the acceptor phase solvent, and modulation of acceptor phase flow rate. Several representative analytes were used to evaluate this approach with spiked, complex sample matrices, including primary wastewater effluent and artificial urine. Also reported are improved measured detection limits in the low part‐per‐trillion range, using a ‘stopped‐flow’ acceptor mode. Copyright © 2015 John Wiley & Sons, Ltd.     

Rapid method for the analysis of plutonium isotopes in a soil sample within 60 min.

A rapid method for the determination of Pu isotopes in a soil sample within 60 min of starting sample pretreatment was developed. The large reduction in the analysis time was attained by the rapid and perfect digestion of the sample using an alkaline fusion method with an induction heating machine. Pu concentrations were then determined by flow injection/ICP-MS using a solid extraction resin after preconcentration by batch extraction with a chelate resin. The limits of detection for 239Pu and 240Pu were 9.2 fg and 4.3 fg, corresponding to 0.03 and 0.05 Bq kg(-1), respectively, under our analytical conditions, which satisfy the lower detection limits (0.5 Bq kg(-1) of 239Pu, and 2 Bq kg(-1) of 240Pu) required for rapid analysis techniques by the Ministry of Education, Culture, Sports, Science and Technology, Japan. This method provides a powerful and practical technique for emergency monitoring in and around nuclear facilities that handle large amounts of plutonium.     

A polydimethylsiloxane/glass capillary electrophoresis microchip for the analysis of biogenic amines using indirect fluorescence detection

A polydimethylsiloxane-glass capillary microchip is fabricated for the rapid analysis of a mixture of common biogenic amines using indirect fluorescence detection. Using a running buffer of phosphate and 2-propanol, and Rhodamine 110 as a background fluorophore, both co-ionic and counter-ionic systems are explored. Studies demonstrate the separation and analysis of cations using indirect fluorescence detection for the first time in a chip-based system. Resulting electrophoretic separations are achieved within a few tens of seconds with detection limits of approximately 6 microM. The reduced sample handling and rapid separations afforded by the coupling of indirect fluorescence detection with chip-based capillary electrophoresis provide a highly efficient method for the analysis and detection of molecules not possessing a chromophore or fluorophore. Furthermore, limits of detection are on a par with reported chip-based protocols that incorporate precolumn derivatisation with fluorescence detection. The current device circumvents lengthy sample preparation stages and therefore provides an attractive alternative technique for the analysis biogenic amines.     

pH-mediated acid stacking with reverse pressure for the analysis of cationic pharmaceuticals in capillary electrophoresis

When using capillary electrophoresis (CE) for the analysis of biological samples, it is often necessary to employ techniques to overcome peak-broadening that results from having a high-conductivity sample matrix. To improve the concentration detection limits and separation efficiency of cationic pharmaceuticals in CE, pH-mediated acid stacking was performed to electrofocus the sample, improving separation sensitivity for the analyzed cations by 60-fold. However, this method introduces a large titrated acid plug into the capillary. To overcome the limitations this low-conductivity plug poses to stacking, the plug was removed prior to the separation step by applying reverse pressure to force it out of the anode of the capillary. Employing this technique allows for roughly twice the volume of sample to be injected. A maximum sample injection time of 240 s was attainable with baseline peak resolution compared to a maximum sample injection time of 120 s without reverse pressure, leading to a twofold decrease in the limits of detection of the analytes used. Separation efficiency overall is also improved when utilizing the reverse pressure step. For example, a 60 s sample injection time results in 94,000 theoretical plates as compared to 60,500 theoretical plates without reverse pressure. This reverse-pressure method was used for detection and quantitation of several cationic pharmaceuticals that were prepared in Ringer's solution to simulate microdialysis sampling conditions.     

Quasi-flow injection analysis for rapid determination of caffeine in tea using the sample pre-treatment method with a cartridge column filled with polyvinylpolypyrrolidone

The sample pre-treatment method using a polyvinylpolypyrrolidone (PVPP) cartridge column combined with a quasi-flow injection analysis (quasi-FIA) system realized the rapid determination of caffeine in three types of tea, green, oolong and black tea. The measurement time for each tea sample pre-treated using a PVPP cartridge column was shortened to 20s. In the present system, the limits of detection and quantification were 0.3 microM (1.5 pmol injected) and 0.7 microM (3.5 pmol injected), respectively, and a linear calibration curve was afforded up to 800 microM (4 nmol injected). Within-run precision of analysis of standard solutions of 10 and 100 microM caffeine was 0.11 and 0.16% (n=6), respectively. Between-run precision of analysis of the same solutions over 6 days was 0.78 and 0.74% (n=6), respectively. Comparison with the conventional HPLC method indicated that the present quasi-FIA method using sample pre-treatment with a PVPP cartridge column was useful for the simple and precise determination of caffeine in green, oolong and black tea samples.     

Comparison of ion chromatographic methods based on conductivity detection, post-column-reaction and on-line-coupling IC-ICP-MS for the determination of bromate

An established method for the determination of the disinfection by-product bromate is ion chromatography (IC). This paper presents a comparison of three IC methods based on either conductivity detection (IC-CD), a post-column-reaction (IC-PCR-VIS) or the on-line-coupling with inductively coupled plasma mass spectrometry (IC-ICP-MS). Main characteristics of the methods such as method detection limits (MDL), time of analysis and sample pretreatment are compared and applicability for routine analysis is critically discussed. The most sensitive and rugged method is IC-ICP-MS, followed by IC-PCR-VIS. The photometric detection is subject to a minor interference in real world samples, presumably caused by carbonate. The lowest sensitivity is shown by the IC-CD method as slowest method compared, which, in addition, requires a sample pretreatment. The highest amount of information is delivered by IC-PCR-VIS, which allows the simultaneous determination of the seven standard anions and bromate.     

Comparison of ion chromatographic methods based on conductivity detection, post-column-reaction and on-line-coupling IC-ICP-MS for the determination of bromate

An established method for the determination of the disinfection by-product bromate is ion chromatography (IC). This paper presents a comparison of three IC methods based on either conductivity detection (IC-CD), a post-column-reaction (IC-PCR-VIS) or the on-line-coupling with inductively coupled plasma mass spectrometry (IC-ICP-MS). Main characteristics of the methods such as method detection limits (MDL), time of analysis and sample pretreatment are compared and applicability for routine analysis is critically discussed. The most sensitive and rugged method is IC-ICP-MS, followed by IC-PCR-VIS. The photometric detection is subject to a minor interference in real world samples, presumably caused by carbonate. The lowest sensitivity is shown by the IC-CD method as slowest method compared, which, in addition, requires a sample pretreatment. The highest amount of information is delivered by IC-PCR-VIS, which allows the simultaneous determination of the seven standard anions and bromate.     

Pesticide analysis by micellar electrokinetic capillary chromatography

On-capillary sample concentration using sample stacking for the improvement of detection limits for various pesticides separated by micellar electrokinetic capillary chromatography was examined. The dependence of the stacking on different parameters was investigated. An approximately 30-fold preconcentration was achieved by applying sample stacking. Employing a two-step enrichment process (solid-phase extraction combined with sample stacking), detection limits were improved and the sample volume for SPE was reduced. In addition, the total time for the analysis was considerably reduced. Detection limits were between 0.01 and 0.1 ng/ml under these enrichment conditions.     

Fast analysis of glycosides based on HKUST‐1‐coated monolith solid‐phase microextraction and direct analysis in real‐time mass spectrometry

Glycosides are a kind of highly important natural aromatic precursors in tobacco leaves. In this study, a novel HKUST‐1‐coated monolith dip‐it sampler was designed for the fast and sensitive analysis of trace glycosides using direct analysis in real‐time mass spectrometry. This device was prepared in two steps: in situ polymerization of monolith in a glass capillary of dip‐it and layer‐by‐layer growth of HKUST‐1 on the surface of monolith. Sufficient extraction was realized by immersing the tip to solution and in situ desorption was carried out by plasma direct analysis in real time. Compared with traditional solid‐phase microextraction protocols, sample desorption was not needed anymore, and only extraction conditions were needed to be optimized in this method, including the gas temperature of direct analysis in real time, extraction time, and CH₃COONH₄ additive concentration. This method enabled the simultaneous detection of six kinds of glycosides with the limits of detection of 0.02–0.05 μg/mL and the linear ranges covering two orders of magnitude with the limits of quantitation of 0.05–0.1 μg/mL. Moreover, the developed method was applied for the glycosides analysis of three tobacco samples, which only took about 2 s for every sample.     

On-line coupled ion chromatography-ICP-(AES, MS) and electro thermal vaporisation-ICP-MS in use for ultra trace analysis of high purity rhenium

This work presents the benefits of coupling techniques such as Electro Thermal Vaporisation (ETV)-ICP-MS and Ion Chromatography (IC)-ICP-(AES, MS) for ultra trace analysis in a high purity rhenium powder sample. Direct analysis using ICP-AES suffers from poor detection limits and allows trace analysis only above 1 g/g for most analytes. ICP-MS analysis of trace elements is more sensitive, but signal depression caused by the heavy Re-ions limits trace analysis to concentrations of 50–100 ng/g analyte in the solid sample. Coupling Ion Chromatography with ICP-spectrometers, combined with time resolved measurement (IC-ICP-TRM) of the elution signals, was used to enhance the sensitivity of both ICP-AES and ICP-MS. Resulting detection limits are in the very low ng/g to pg/g range. Coupling of ETV and ICP-MS offers the possibility of eliminating the volatile Re₂O₇ matrix by thermal pretreatment and allows ICP-MS measurements without matrix interferences caused by Re. Results from these methods are compared with Glow Discharge Mass Spectrometry (GDMS) analysis, a semiquantitative solid state technique. The results are also compared with the manufacturers' specifications to show the power of modern routine analysis using ICP-AES or FAAS.     

On-line trace enrichment for the simultaneous determination of microcystins in aqueous samples using high-performance liquid chromatography with diode-array detection.

The need for a rapid, sensitive and reliable analytical method for cyanobacterial toxins, microcystins, has been emphasized by the awareness of toxic cyanobacteria as a human-health risk through drinking water. A new high-performance liquid chromatographic method with column switching was developed for the determination of microcystin-LR, -RR and -YR from water samples without pre-purification. The filtered water sample was passed through a Zorbax CN precolumn at a flow-rate of 3 ml/min for on-line trace enrichment. After valve switching, concentrated analytes were eluted in back-flush mode and separated on a Luna C18 column with a gradient of acetonitrile -20 mM phosphate buffer (pH 2.5). The method showed excellent precision, accuracy and speed with detection limits of 0.02 microgram/ml from 100 ml of surface water. The total analysis time per sample was about 90 min. This method improves reliability, sensitivity and sample throughput, and shortens the analysis time compared to analysis methods using off-line solid-phase extraction.     

Fast quantitative determination of platinum in liquid samples by laser-induced breakdown spectroscopy

The potential of laser-induced breakdown spectroscopy (LIBS) for the rapid determination of platinum in liquid silicone oils has been evaluated in the framework of on-line process control. A comparison of LIBS sensitivity between three setups designed for liquid analysis (static, liquid jet and flowing liquid) was performed using a 266 nm Nd/YAG laser irradiation. Best results were obtained using the flowing liquid setup and a similar limit of detection was obtained using the liquid jet. The effect of different buffer gases (Ar, He, N(2), etc.) on the signal sensitivity was studied in liquid jet analysis and best values were obtained with a nitrogen sheath gas. Detection limits were in the 100 mg/kg range for both setups. Quantitative determination of platinum in real liquid samples was also investigated using both liquid jet and flowing liquid setups. Calibration curves were plotted for Pt with the liquid jet and the flowing liquid setups under optimised temporal acquisition parameters (delay time and gate width). A normalisation using a silicon line was applied and recovery ranged from 3 to 15% for Pt in catalyst samples with both setups showing that LIBS is a sensitive and accurate method for on-line applications.     

Measurement of penicillamine and N-acetylcysteine in human blood by high-performance liquid chromatography and electrochemical detection

A rapid and precise high-performance liquid chromatographic assay for both N-acetylcysteine and penicillamine in blood samples is described using selective reductive electrochemical detection and a high-efficiency C18 reversed-phase column. The use of an internal standard compensated for changes in detector responses during a run and for variable sample recovery. The detection limits for N-acetylcysteine and penicillamine were 25 and 10 ng/ml, respectively, using 500-microliters blood samples. Reproducibility of measurement for both thiols was excellent. This method allows routine monitoring of blood levels and pharmacokinetic studies with N-acetylcysteine and penicillamine.     

Fluorometric fiber optic drop sensor for atmospheric hydrogen sulfide

A fluorometric technique based on a liquid drop excited from its interior by an optical fiber is described for the measurement of low concentrations of atmospheric hydrogen sulfide (H(2)S). A drop of alkaline fluorescein mercuric acetate (FMA) solution is suspended in a flowing air sample stream and serves as a renewable sensor. An optical fiber contained within the conduit that forms the drop, brings in the excitation beam; the fluorescence emission is measured by an inexpensive photodiode positioned close to the drop. As H(2)S in the sample is collected by the alkaline drop, it reacts rapidly with FMA resulting in a significant decrease in fluorescence intensity, proportional to the concentration of H(2)S sampled. The chemistry of this uniquely selective reaction has been well established for many years; the present technique permits a simple fast inexpensive near real-time measurement with very little reagent consumption. Even without prolonged sampling/preconcentration steps, limits of detection (LODs) in the double digit ppbv range is readily attainable.     

Comparison between the diurnal trends of ozone and radon gas concentrations measured at ground in the semi-rural site of Central Italy

The effectiveness of a Compton suppression system (CSS) for instrumental neutron activation analysis of plant materials was evaluated. Suppression factors were measured with ¹³⁷Cs sources. Five certified reference materials were analyzed and the detection limits calculated from both suppressed and unsuppressed spectra were compared. The CSS demonstrated to be useful for lowering the detection limits of ten out of sixteen elements tested, showing a maximum improvement factor of 3.9. The system performance was strongly influenced by the sample composition and also by the measurement conditions, indicating the importance of testing each individual sample type and analytical protocol.