Peter Leonhard

Analysis of diluted sea-water at the ng L−1 level using an ICP-MS with an octopole reaction cell

An ICP-MS with an octopole reaction/collision cell was used for the multi-element determination of trace elements in sea-water. The use of a reaction or collision gas, respectively, reduces serious spectral interferences from matrix elements such as ArCl+ or ArNa+. On introducing He or H2 to the cell, detection limits of 0.3 ng L−1 for U to 20 ng L−1 for Fe and As were determined in 10-fold diluted sea-water. The trace elements V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Pb and U were determined in diluted sea-water samples (certified reference material: NASS-5, SLEW-3) with a trueness of ±20% to the certified values. For most of the elements an accuracy of better than 19% was achieved with no sample pre-treatment other than simple dilution.

Determination of phosphorus in phosphorylated deoxyribonucleotides using capillary electrophoresis and high performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry with an octopole reaction cell

The determination of phosphorus in a biologically relevant sample matrix such as DNA is described. The analytical methodology used is based on a robust on-line coupling of capillary electrophoresis (CE) or high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry, equipped with an octopole reaction system (ORS-ICP-MS). Polyatomic ions formed in the plasma and the interface region of the ICP-MS that interfere with the determination of P at mass 31 were minimised by the addition of helium to the collision cell. Instrumental detection limits of 125 ng L−1 for 31P, and in the range of 18 to 49 ng L−1 for the other trace elements, were achieved under the conditions described. In order to demonstrate the high separation and detection efficiency of the system, the method developed has been applied to the element specific detection of phosphorus in monophosphorylated deoxynucleotides and to enzymatically digested calf thymus DNA after CE and HPLC separation, respectively. Both hyphenated techniques provide baseline separation of the four deoxynucleotide monophosphates (dNMP), which are present in the DNA chain. With CE-ICP-MS, detection limits for phosphorus down to 53 µg L−1 (2′-deoxyguanosin-5′-monophosphate, dAMP) (corresponding to 0.6 pg P absolute) have been achieved. RSDs of the migration times were about 5%. Using HPLC-ICP-MS, detection limits down to 3 µg L−1 (2′-deoxythymidine-5′-monophosphate, dTMP) (corresponding to 0.03 ng P absolute) were obtained. The migration/elution order of the deoxynucleotides investigated was obtained by comparison with the migration/retention times of commercially available dNMPs. Furthermore it was checked if HPLC-ESI-MS can be operated under the same chromatographic conditions for the confirmation of the elution order and for the characterisation of unknown peaks. Finally, flow injection analysis (FIA) was used for the quantification of the phosphorus content in the dNMP samples. Using FIA, detection limits for phosphorus of 2.5 µg L−1 corresponding to 25 pg phosphorus absolute were achieved.

Sensitive, simultaneous determination of P, S, Cl, Br and I containing pesticides in environmental samples by GC hyphenated with collision-cell ICP-MS

A sensitive and highly selective methodology for the determination of a wide range of pesticides, based on the simultaneous element-specific determination of phosphorus, sulfur, chloride, bromine and iodine by gas chromatography hyphenated with octopole reaction cell-inductively coupled plasma mass spectrometry (GC-CC-ICP-MS) is described. The chromatographic system was optimised for separation efficiency and short run times and was coupled via a commercially available interface with an octopole reaction cell ICP-MS system which is equipped with an on-axis collision cell. Instrumental settings were optimised with respect to high sensitivity for the target nuclides 31P, 32S, 35Cl, 79Br and 127I and minimized background levels especially for the ions most affected by interferences, such as 31P+, 32S+. Helium and nitrogen were tested as additional plasma gases for possible sensitivity enhancement of the element-specific detection resulting from improved ionisation processes inside the plasma. Due to the multi-element capability of the instrumental setup and the good accuracy of the retention times that were achieved, identification of the detected pesticides can be carried out using their retention times, the element compositions and element ratios present in each chromatographic peak. For the different pesticides detection limits down to the ppt level or the low ppb level were obtained. The average RSDs of the retention times and the peak areas were better than 0.8% and 8%, respectively. The analytical methodology developed has been applied to the screening of different fruit extracts for pesticides. Peaks were identified by comparison of the retention times obtained and by their elemental composition. Quantitative results have been obtained both by external calibration and by using a compound independent calibration.

Investigation of the sulfur speciation in petroleum products by capillary gas chromatography with ICP-collision cell-MS detection

Recent regulations concerning the low-sulfur gasoline require analytical methods able to provide specific information on sulfur containing compounds present in petroleum products at the ng g−1 range. The on-line coupling of capillary GC with ICP-collision cell-MS was proposed for the speciation of sulfur in hydrocarbon matrices. The technique showed an absolute detection limit 0.5 pg for a 1 µL sample injected in the splitless mode which is about two orders of magnitude lower than the currently used techniques.

First experimental proof of asymmetric charge transfer in ICP-MS/MS (ICP-QQQ-MS) through isotopically enriched oxygen as cell gas

The quantification of a variety of elements in the field of ICP-MS is restricted by isobaric interferences. The recent development of ICP-MS/MS (“triple quadrupole” configuration) offers a new way to solve the problem of the detection of such elements affected by interferences because the signal caused by either the analyte or the isobaric interference can be shifted to another m/z through reactions with the cell gas (oxygen, ammonia or hydrogen). This system consists of two quadrupoles (Q1 and Q2) with a collision/reaction cell in between. When using the MS/MS mode of this configuration it becomes possible to restrict the ions entering the cell to a defined m/z and therefore get a better insight into the reactions possibly occurring within the collision/reaction cell. While using oxygen as a cell gas analyte ions can undergo oxygen transfer as well as asymmetric charge transfer reactions. As a proof for the latter reaction two types of measurements have been carried out, using both oxygen with natural isotopic composition and isotopically enriched oxygen (97% 18O2) as cell gases.

Analysis of boronic acids by nano liquid chromatography-direct electron ionization mass spectrometry.

A new method, based on a direct-electron ionization (EI) interface, is presented for the analysis of compounds insufficiently amenable to usual MS methods. The instrumentation is composed of a nano liquid chromatograph (LC) and a mass spectrometer (MS) directly coupled by a transfer capillary. The eluent is directly introduced into the heated electron impact ion source of the MS. Significant advantages are the generation of reproducible spectra and the ability to ionize highly polar compounds. Boronic acids are used as coupling reagents to produce drugs, agrochemicals, or herbicides. The purity of educts is of high importance because impurities in the educt are directly associated with impurities in the product. Because of their high polarity and tendency to form boroxines, boronic acids require derivatization for GC analysis. The presented nano-LC-EI/MS method is easily applicable for a broad range of boronic acids. The method shows good detection limits for boronic acids up to 200 pg, is perfectly linear, and shows a very high robustness and reproducibility. A mixture of compounds could easily be separated on a monolithic RP18e column. The method represents a new, simple, robust, and reproducible approach for the detection of polar analytes. It is a good candidate to become a standard method for industrial applications.

Nano-liquid chromatography-direct electron ionization mass spectrometry: improving performance by a new ion source adapter.

A novel interface adapter has been designed to provide a new way of directly coupling a nano-liquid chromatograph to an electron ionization mass spectrometer. It connects the transfer capillary coming from the liquid chromatograph to the ionization chamber and can be easily screwed into the ion source. Liquid coming from the column passes through the heated adapter flow path and is vaporized. A continuous flow of new liquid pushes the vapor into the ionization chamber where it is ionized and continues on to the mass analyzer. The advantages of the new adapter are reduced ice formation inside the ion source and less clogging of the transfer capillary. Improvements achieved are demonstrated on the basis of caffeine and steroid analysis. The limits of detection of selected steroids are compared with and without the adapter. The adapter improves the detection limit of the system by a factor of 2 and precision from ≤15% to ≤9% relative standard deviation. No derivatization procedure is necessary before the analysis of small polar compounds. The resulting spectra are reproducible, easily interpretable, and database searchable. The new method is robust, delivers reproducible results, and provides a highly efficient alternative to existing methods in the field of pharmaceutical analysis.