Analytical Chemistry

XPS & XRF

by farshad akhtarian

Characterization and optimization of an online system for the simultaneous measurement of atmospheric water-soluble constituents in the gas and particle phases

by Trevor Vandenboer

Milos Z. Markovic, Trevor C. VandenBoer and Jennifer G. Murphy

DOI: 10.1039/c2em00004k

In this work we present the results of extensive characterization and optimization of the Ambient Ion Monitor-Ion... more In this work we present the results of extensive characterization and optimization of the Ambient Ion Monitor-Ion Chromatograph (AIM-IC) system, an instrument developed by URG Corp. and Dionex Inc. for simultaneous hourly measurements of the water-soluble chemical composition of atmospheric fine particulate matter (PM2.5) and associated precursor gases. The sampling assembly of the AIM-IC consists of an inertial particle size-selection assembly, a parallel-plate wet denuder (PPWD) for the
collection of soluble gases, and a particle supersaturation chamber (PSSC) for collection of particles, in series. The analytical assembly of the AIM-IC consists of anion and cation IC units. The system detection limits were determined to be 41 ppt, 5 ppt, and 65 ppt for gas phase NH3(g), SO2(g), andHNO3(g) and 29 ng m^
3, 3 ng m^3, and 45 ng m
^3 for particle phase NH4+, SO42-, and NO3- respectively. From external trace gas calibrations with permeation sources, we determined that the
AIM-IC is biased low for NH3(g) (11%), SO2(g) (19%), and HNO3(g) (12%). The collection efficiency of SO2(g) was found to strongly depend on the composition of the denuder solution and was found to be the most quantitative with 5 mM H2O2 solution for mixing ratios as high as 107 ppb. Using a cellulose
membrane in the PPWD, the system responded to changes in SO2(g) and HNO3(g) within an hour, however for NH3(g), the timescale can be closer to 20 h. With a nylon membrane, the instrument response time for NH3(g) was significantly improved, becoming comparable to the responses for SO2(g) and HNO3(g). Performance of the AIM-IC for collection and analysis of PM2.5 was evaluated by generating known number concentrations of ammonium sulfate and ammonium nitrate particles (with an aerodynamic diameter of 300 nm) under laboratory conditions and by comparing AIM-IC measurements to measurements from a collocated Aerosol Mass Spectrometer (AMS) during a fieldsampling campaign. On average, the AIM-IC and AMS measurements agreed well and captured rapid ambient concentration changes at the same time. In this work we also present a novel inlet configuration and plumbing for the AIM-IC which minimizes sampling inlet losses, reduces peak
smearing due to sample carryover, and allows for tower-height sampling from the base of a research tower.

Pre-Analytical Errors in Blood Homocysteine Assays

by Vinod Bhagwat

Miniaturised selective pressurised liquid extraction of polychlorinated biphenyls from foodstuffs

by Christian Dietz

J.J. Ramos, C. Dietz  M.J. González, L Ramos, published in J. Chromatogr. A, 1152, (2007), 254-261.

The feasibility of miniaturised pressurised liquid extraction (PLE) with in-cell purification and subsequent gas... more The feasibility of miniaturised pressurised liquid extraction (PLE) with in-cell purification and subsequent gas chromatography with microelectron capture detection (GC–micro-ECD) for the determination of prioritary and toxic polychlorinated biphenyls (PCBs) in a variety of foodstuffs (fat contents in the range 22–49%, w/w, on a freeze-dried basis) has been investigated. After optimisation of the several experimental parameters affecting the efficiency of the selective PLE process, the developed method provided quantitative recoveries of the endogenous PCBs studied and complete fat elimination in a single step using n-hexane as extraction solvent. A total solvent volume of 3.5mL was used for the two consecutive 7 min static PLEs of 100-mg samples. Detection limits using GC–micro-ECD were below 0.2 ng/g freeze dried sample for all 22 PCBs investigated in real-life foodstuffs, and the repeatability of the complete PLE plus GC–micro-ECD method as calculated for the analysis of the endogenous PCBs in general was better than 14%. Comparison of the miniaturised PLE method developed with either conventional Soxhlet extraction or matrix solid phase dispersion with subsequent (off-line) clean-up for the analysis of non-spiked samples showed that the efficiency of PLE was similar to or better (recoveries in the range 83–133%, as calculated for the endogenous analytes) than for the other two extraction methods assayed.

Current perspectives in analyte extraction strategies for tin and arsenic speciation

by Christian Dietz

C. Dietz, J. Sanz, E. Sanz, R. Muñoz-Olivas, C. Cámara, published in J. Chromatogr. A .1153 (2007), 114-129.

Nowadays, reliable and robust detectors can be considered standard laboratory instrumentation, which, for most of the... more Nowadays, reliable and robust detectors can be considered standard laboratory instrumentation, which, for most of the elements provide quantitation limits in the lower ng/g range. Despite these advances in detector technology, sample preparation is by far the most important error source in modern analytical method development and can be judged as the “Achilles’ heel” of any analytical process regarding reliability of the obtained results and time consumption. The aim of the present review is to highlight modern trends for tin and arsenic speciation, as these analytes can be considered as models for challenges in modern method development in this field. First background information, legislative aspects and current needs are elucidated. Then the role of sample  treatment within the process of method development in speciation is discussed, followed by a presentation of modern extraction techniques, matching the requirements for arsenic  nd tin speciation analysis: to provide mild conditions in order to ensure species preservation, to improve species recovery, to enhance sample throughput and to be suitable for hyphenation with chromatographic separation systems. The review includes applications on tin and arsenic speciation, covering the period of 2001–2006.

Alternative extraction methods for arsenic speciation in hair using ultrasound probe sonication and pressurised liquid extraction

by Christian Dietz

E. Sanz, R. Muñoz-Olivas, C. Dietz, J. Sanz, C. Cámara, published in J. Anal. Atom. Spectrom. 22, (2007),131-139.

The methods for arsenic speciation in hair currently available are scarce and highly time consuming, especially during... more The methods for arsenic speciation in hair currently available are scarce and highly time consuming, especially during sample preparation. This work presents alternative methods providing better recoveries and similar species distribution compared with established methods, but the extraction time is reduced from about 6 h to only a few minutes. First, several extraction media were studied and evaluated using ultrasound probe sonication. Either a solution of 0.5% performic acid or an enzymatic treatment (mixture of lipase and protease in aqueous media) was selected as the best treatment, which allowed us to reduce the extraction time to 5 or 10 min, respectively, achieving a slightly higher species recovery in the latter case. Second, a laboratorymade miniaturised device for pressurised liquid extraction is employed and compared with the previous methods. Initially, temperature, pressure and extraction time were optimised by applying chemometrics, in particular the use of a multivariate experimental design and analysis of variance. In order to improve the obtained results, additional variables such as type of solvent, particle size of dispersant medium and number of extraction cycles were further optimised. Optimum conditions were obtained using a mixture of 1% SDS and 5%  isopropanol as extraction solvent at a temperature of 125 ºC and an applied pressure of 6 MPa for two cycles of 5 min each. The optimal particle size of dispersant was 35 micro-m. Total arsenic was determined by ICP-MS and the species  present in hair were quantified by HPLC-ICP-MS. For method validation a Certified Reference Material (Human Hair GBW 07601) was used all throughout this study.

Accelerated Extraction for determination of Polycyclic Aromatic Hydrocarbons in Marine Biota

by Christian Dietz

J. Sanz Landaluze, L. Bartolomé, O. Zuloaga, L. González, C. Dietz, C. Cámara, published in Anal. Bioanal. Chem. 384 (2006), 1331- 1340.

A rapid and simple method is proposed for determination of polycyclic aromatic hydrocarbons (PAH) in complex matrices... more A rapid and simple method is proposed for determination of polycyclic aromatic hydrocarbons (PAH) in complex matrices such as marine biota. The method uses sonication, bymeans of an ultrasonic probe, as a new tool for assisted extraction, coupled with reversed-phase liquid chromatography (RP-LC) with fluorescence detection (FL) for determination of 16 US EPA priority PAH. Separation and detection of the 16 PAHwere complete in 45 min by RPLC with a C18 column and acetonitrile–water gradient elution. Multivariate optimisation of the variables affecting extraction (ultrasound radiation amplitude, sonication time, and temperature of the water-bath in which the extraction cell was placed) was conducted. The accuracy of the method was determined by analysis of a certified reference material and comparison of the results obtained with those from another method (microwave-assisted extraction and GC– MS). The new technique avoids the main problems encountered in the determination of PAH in complex matrices such as marine biota, and no clean-up step is necessary. The method was applied to determination of PAH in estuarine biota samples from the Urdaibai estuary (Biscay, Spain).

Recent Developments In Solid-Phase Microextraction Coatings and Related Techniques

by Christian Dietz

C. Dietz, J. Sanz, C. Cámara, published in J. Chromatogr. A 1103 (2006), 183-192.

During the last decade, solid-phase microextraction (SPME) has gained widespread acceptance for analyte matrix... more During the last decade, solid-phase microextraction (SPME) has gained widespread acceptance for analyte matrix separation and preconcentration. Relatively few data are currently available dealing with in-house production of fibres with tailor-made properties to be used for SPME, though recently the number of publications evaluating new coatings has been considerably growing. This review, centred on publications that appeared during the last five years, is resuming different approaches which can be used for fibre production and further summarises alternative techniques closely related to SPME, such as in-tube extraction or single-drop microextraction (SDME). The aim is to give the reader a concise overview of recent developments in new coating procedures and materials, including the respective applications.

Materiales de Referencia - uso, terminología y ayuda en la red

by Christian Dietz

C. Dietz, published in Boletín de la Sociedad Española de Química Analítica 12, (2005), 5-8.

A guide to the use of Certified Reference Materials for validation of an analytical method. With hints for searching... more A guide to the use of Certified Reference Materials for validation of an analytical method. With hints for searching CRM´s matching the needs and troubleshooting.
In spanish language..

SPME – multicapillary GC coupled to different detection systems applied to volatile organo-selenium speciation in yeast

by Christian Dietz

C. Dietz, J. Sanz, P. Ximénez-Embún, Y. Madrid, and C. Cámara, published in J. Anal. Atom. Spectrom. 19, (2004), 260-266.

In this work the versatility of solid phase microextraction (SPME) in combination with multicapillary gas... more In this work the versatility of solid phase microextraction (SPME) in combination with multicapillary gas chromatography (MC–GC) was evaluated using different common detectors for organo-selenium speciation. The methods compared for detection were inductively coupled plasma mass spectrometry (ICP–MS), microwave induced plasma atomic emission spectroscopy (MIP–AES) and atomic fluorescence spectroscopy (AFS). All detectors were found to be suitable, with highest sensitivity being obtained for MIP–AES detection, with detection limits of 0.57 ng ml, for dimethyl selenide, 0.47 ng ml for diethyl selenide and 0.19 ng ml.for dimethyl diselenide. The method was applied to the determination of volatile alkyl selenides in selenium enriched yeast samples, which revealed that the presence of inorganic selenium gives rise to at least seven different volatile species after metabolization, with dimethyl diselenide the predominant species. Commercial pasteurized yeast, containing mainly selenomethionine for its use as a food supplement, was found to be still active and produces considerable amounts of organoselenium compounds.

Volatile organoselenium speciation in plants by SPME - moderate temperature multicapillary gas chromatography with MIP-AES detection

by Christian Dietz

C. Dietz, J. Sanz, P. Ximénez-Embún, Y. Madrid, and C. Cámara, published in Anal. Chim. Acta. 501, (2004), 157-167.

Microwave induced plasma atomic emission spectrometry (MIP-AES) in combination with multicapillary (MC) gas... more Microwave induced plasma atomic emission spectrometry (MIP-AES) in combination with multicapillary (MC) gas chromatography could be proven to be useful for element specific detection of volatile species. Solid phase microextraction (SPME)was used for preconcentration and sample-matrix separation. The fiber desorption unit as well as the heating control for theMCcolumn were in-house developed and multicapillary column was operated at moderate temperatures (30–100 ◦C). The method was optimized for organo-selenium species (dimethylselenide (DMSe), diethylselenide (DEtSe) and dimethyldiselenide (DMDSe)), using a chemometric approach. Stationary phases for the separation column were optimized using a conventional GC and contrasted with the results obtained with the MC. Application was focussed on selenium accumulating biological matter, such as lupine, yeast, Indian mustard and garlic. These samples were grown in hydroponic solution containing inorganic selenium (Na2SeO3 and Na2SeO4). SPME sampling was carried out in fixed volume flow boxes in headspace above the living plants and in vials using treated samples. Results demonstrate inorganic selenium transformation into volatile organic species during metabolism. Separation is fast, a chromatogram can be obtained in less than 3 min and detection limits were at sub-ppb level for all investigated species. The system is independent from the use of a conventional gas chromatographic oven and can be used as a versatile alternative to highly cost intensive methods such as GC–ICP-MS.

Volatile organoselenium monitoring in production and gastric digestion processes of selenized yeast by Solid Phase microextraction - multicapillary gas chromatography coupled to microwave induced plasma atomic emission spectrometry

by Christian Dietz

C. Dietz, J. Sanz Landaluze, P. Ximénez-Embún Y., Madrid-Albarrán, C. Cámara, published in Appl. Organomet. Chem. 18 (2004), 606-613.

Evolution of volatile organoselenium compounds in the production and gastric digestion of selenized yeast has been... more Evolution of volatile organoselenium compounds in the production and gastric digestion of selenized yeast has been monitored. The industrial production of these kinds of material, employed as food supplements, has been simulated in a process of yeast enrichment with inorganic selenium selenium (IV) in different growth media, with variation of the pH value. The in vitro gastric digestion process was carried out with pepsin in an acid and salt mixture. Determination of volatile species of selenium was achieved coupling solid-phase microextraction (SPME) for preconcentration and sample–matrix separation and microwave-induced plasma atomic emission spectrometry, in combination with multicapillary (MC) gas chromatography for separation and detection of the selenium species. The MC column was operated at low temperatures (∼30 ◦C). The method was optimized, using a chemometric approach, with respect to the detection of organoselenium species such as dimethylselenide, diethylselenide and dimethyldiselenide. SPME sampling was carried out in the headspace above the corresponding solutions. Separation is fast, with a chromatogram being obtained in less than 5 min, and the detection limits were at the low parts per billion level for all species investigated. The results of the yeast enrichment process demonstrate inorganic selenium transformation into volatile organic species. The presence of inorganic selenium gave rise to at least five different volatile species after metabolization by yeast, with dimethylselenide and dimethyldiselenide being the predominant species. Commercial pasteurized yeast, containing mainly selenomethionine for use as a food supplement, and tablets were found to be still active under conditions of the simulation of the digestion process, even though producing relatively low amounts of organoselenium compounds.

Mercury speciation using the Capillary Cold Trap coupled with microwave induced plasma atomic emission spectrometry

by Christian Dietz

C. Dietz, Y. Madrid, and C. Cámara, published in J. Anal. Atom. Spectrom.(2001), 16, 1397-1402.

In this paper the capillary cold trap (CCT) is presented as a novel sample introduction and separation system for... more In this paper the capillary cold trap (CCT) is presented as a novel sample introduction and separation system for microwave-induced plasma detection. The method is based on cryogenic trapping and gas chromatographic separation carried out within the same capillary. The device, which comprises a derivatization step, on-line gas phase extraction, preconcentration and analyte separation, is semi-automated and all operational parameters are adjustable via an in-house developed control unit, regulating the selected parameters throughout the analysis process. Detection was carried out using a 2.45 GHz microwave-induced argon discharge sustained in a TM010 Beenakker cavity and emission lines were recorded by means of a ST6-UV CCD camera provided by the Santa Barbara Instrument Group. The detection limits achieved were 6.0, 0.95 and 1.25 ng L21 for dimethylmercury, methylmercury and inorganic mercury, respectively. A complete chromatogram could be obtained within 3 min, resulting in the duration of one whole analysis cycle of about 15 min. The proposed method was validated by the analysis of a reference material (BCR 710) and applied to mercury speciation in different sample matrices such as oyster, tuna fish and sediments after microwave-assisted extraction. The total mercury concentration in real samples was in the range of 0.2–11 mg kg21, of which up to 75% corresponded to organic mercury species.

SPME for on-line volatile organic selenium speciation

by Christian Dietz

C. Dietz, T. Perez-Corona, Y. Madrid, and C. Cámara, published in J. Anal. Atom. Spectrom.(2003),18, 467-473.

A method for speciation of volatile organo-selenium compounds is presented, using solid phase microextraction (SPME),... more A method for speciation of volatile organo-selenium compounds is presented, using solid phase microextraction (SPME), thermal desorption by an in-house developed desorption unit and detection by different detectors such as AAS and ICP-MS. The procedure is simple, efficient, fast and solvent free. Dimethylselenium and dimethyldiselenium could be separated and quantified in less than two minutes, achieving detection limits of 0.7 and 0.9 mg L21, respectively, when ICP-MS detection was used. No additional chromatographic system for the species separation was needed. A broad range of fiber coatings were compared, finding that commonly used stationary phases such as PDMS show a highly reduced affinity for the investigated species. The method was applied to quantification of organo-selenium content in garlic samples.

The capillary cold trap as a suitable instrument for mercury speciation by volatilization, cryogenic trapping and gas chromatography coupled with atomic absorption spectrometry

by Christian Dietz

C. Dietz, Y. Madrid, P. Quevauvillier and C. Cámara, published in Anal. Chem. (2000), 72, 4178 - 4184.

An innovative accessory for speciation analysis has been developed. The system is based on the combination of... more An innovative accessory for speciation analysis has been developed. The system is based on the combination of cryogenic trapping and gas chromatographic separation, carried out within the same capillary. The instrument, hyphenating derivatization, gas-phase extraction,  preconcentration, and analyte separation, is semiautomated, and all operational parameters are adjustable via an in-housedeveloped control unit, which regulates the selected parameters throughout the analysis process. Species detection was carried out by atomic absorption spectrometry. The detection limits achieved were 33, 39, and 71 ng L-1 for dimethylmercury, methylmercury, and inorganic mercury, respectively. A complete chromatogram could be obtained within three minutes, resulting in the duration of one whole analysis cycle of about 15 min. The proposed method was applied to mercury speciation in freeze-dried tuna fish powder after microwave-assisted extraction, finding that mercury is present at 80% as
methylmercury and about 20% as inorganic mercury, in this kind of biological material.

Simultaneous determination of As, Hg, Se and Sb by hydride generation- microwave induced plasma atomic emission spectrometry after preconcentration in a cryogenic trap

by Christian Dietz

C. Dietz, Y. Madrid, P. Quevauvillier and C. Cámara, published in J. Anal. Atom. Spectrom.(1999), 14, 1349-1355.

In this paper a system is presented which combines hydride generation with a preconcentration step in a cryogenic trap... more In this paper a system is presented which combines hydride generation with a preconcentration step in a cryogenic trap and detection using MIP-AES. The MIP has been operating at atmospheric pressure with a forward power of 30–150 W, using a TM010 cavity (Beenakker resonator), equipped with a tangential flow torch design. The plasma emission was observed end-on by the means of a CCD camera coupled to a 0.5 m Czerny–Turner design monochromator. Metal hydrides were generated batchwise in aqueous medium, preconcentrated in a liquid nitrogen cryogenic trap and then evaporated by electrical heating into the plasma discharge. The optimum working conditions have been found at the 197±7 nm window working with a forward power of 130 W, a plasma gas flow rate of 270 ml min−1 of helium, a carrier gas flow rate of 134 ml min−1 of helium, a NaBH4 concentration of 2% and a HNO3 concentration of 0.66 M. Under these conditions detection limits of 2.0, 13, 2.2 and 3.3 mg L−1 for As, Hg, Se and Sb were achieved. The method was applied to the detemination of these analytes in spiked wastewater samples with recoveries of 95% or higher for all four analytes.

Speciation of Mercury by ICP-MS After on-Line Capillary Cryofocussing and Ambient Temperature Multicapillary Gas Chromatography

by Christian Dietz

Wasik, A.; Rodriguez Pereiro, I.; Dietz, C.; Szupunar, J.; Lobinski, R., published in Anal. Commun. (1998), 35, 331-335.

An automated, small and easily mountable/demountable accessory based on a constant temperature multicapillary GC is... more An automated, small and easily mountable/demountable accessory based on a constant temperature multicapillary GC is proposed for time-resolved introduction of gaseous mercury species into an ICP-MS. The fast, narrow-band injection was achieved by cryofocussing (280 °C) of dimethyl-, methylethyl- and diethylmercury in an 11 cm capillary housed in a steel tube prior to desorption of the species (within 3–5 s) by rapid-pulse high intensity current. The highest chromatographic resolution was achieved at ambient column temperatures; isothermal separations at higher temperatures offered increased sensitivity and speed of analysis controlled by the data acquisition rate of a quadrupole MS. The compatibility of the operating variables with the ICP ionization conditions (argon at 50–300 ml as the carrier gas) and negligible peak broadening on the column and in the ICP-MS interface allow the sensitive (limit of detection 0.15 pg) isotope-selective speciation of mercury in biological and sediment samples.

Determination of Sb using microwave induced plasma atomic emission spectrometry after preconcentration in a cryogenic trap

by Christian Dietz

C. Dietz, Y. Madrid, P. Quevauvillier and C. Cámara, published in Química Analítica (1998)  17, 205-212.

This paper describes a system in which antimony hydride generation with a preconcentration step in a cryogenic trap is... more This paper describes a system in which antimony hydride generation with a preconcentration step in a cryogenic trap is combined with detection using MIP-AES. The MIP operates at atmospheric pressure with a forward power of 30 - 180 Watt, using a TM010 cavity (Beenakker resonator), equipped with a tangential flow torch design, which allows the use of metal-loaded helium or other molecular gases as carrier gas and argon as internal plasma gas. The plasma emission was observed end-on. Antimony hydride was generated batchwise in aqueous medium, preconcentrated in a liquid nitrogen cryogenic trap and then evaporated by electrical heating into the plasma discharge. The optimum working conditions were at 217.6 nm with a forward power of 130 Watt, a plasma gas flow rate of 335 ml/min of argon, a carrier gas flow rate of 134 ml min-1 of helium, a NaBH4 concentration of 0.50 % and acetic acid concentration of  0.87 M. Under these conditions a detection limit of 9 ng of Sb(III) in a total sample volume of 100 ml was achieved. This is about 100-times lower than the corresponding continuous hydride generation. The proposed method has been successfully applied to the determination of Sb in environmental samples.

On-line high-performance liquid chromatography-ultraviolet-nuclear magnetic resonance method of the markers of nerve agents for verification of the Chemical Weapons Convention

by avik mazumder

Determination of hydrolytic degradation products of nerve agents by injection port fluorination in gas chromatography/mass spectrometry for the verification of the Chemical Weapons Convention

by avik mazumder