Fred L. Fricke

Speciation of arsenic in urine using high-performance liquid chromatography with inductively coupled plasma mass spectrometric detection

High-performance liquid chromatography (HPLC) has been coupled with inductively coupled plasma mass spectrometry (ICP-MS) for the speciation of four arsenic compounds commonly found in urine. Arsenite (As3+), arsenate (As5+), dimethylarsinate (DMA) and monomethylarsonate (MMA) were separated via anion-exchange HPLC and detected on-line using ICP-MS. The absolute detection limits ranged from 20 to 91 pg of arsenic in aqueous media and 36–96 pg in urine. The four species were determined in two freeze-dried urine standards using the method of standard additions. The total of the four species was found to be within 13% of the average reported total arsenic concentration for both freeze-dried urine standards containing elevated levels of As5+. The relative standard deviation of peak-height measurements was less than 10% for each of the four species in urine. The determination of As3+ is complicated by the presence of an interfering peak, which is believed to arise from the co-elution of chlorine-containing species and subsequent formation of 40Ar35CI+ ions (m/z= 75).

Elimination of the argon chloride interference on arsenic speciation in inductively coupled plasma mass spectrometry using ion chromatography

Ion chromatography has been combined with inductively coupled plasma mass spectrometry for the speciation of arsenic compounds commonly found in urine. Ion chromatography was used to eliminate or reduce the mass spectral interference formed from chloride, namely argon chloride, by resolving chloride chromatographically from the arsenic compounds. A 20-fold dilution of the urine samples was necessary in order to avoid column overloading from chloride and subsequent argon chloride interference. Detection limits in urine of 3.4 p.p.b. AsIII, 4.2 p.p.b. AsV and 7 p.p.b. dimethylarsinic acid were obtained. Three commercially available freeze-dried urine standards were analysed using the standard additions method. Good agreement was obtained for total arsenic content, which was calculated from the sum of the species with accepted arsenic concentration. The relative standard deviation of peak height for each of the species was approximately 5% in urine.

Detection of halogens as positive ions using a He microwave induced plasma as an ion source for mass spectrometry

Abstract The detection of bromine, chlorine and iodine as positive ions is accomplished by using a helium microwave induced plasma as an ion source with quadrupole mass spectrometric detection. An interface between the microwave cavity and the sampler is described which improves the degree of ionization of Br, Cl and I by reduction of NO+ in the He plasma. The effects of sampling depth, plasma power and He/N2 flow rate on ion signal are discussed. Major background ions present in the He plasma are presented. Preliminary detection limits for Br+, Cl+ and I+ 1.2, 21 and 1.8 pg s respectively.

Electrothermal vaporisation interface for sample introduction in inductively coupled plasma mass spectrometry

An electrothermal vaporisation (ETV) device was developed for inductively coupled plasma mass spectrometry by modifying a commercial graphite furnace unit. A detailed description of the modifications are presented. The new ETV interface is designed to increase sample transport efficiency by converting analyte vapour into micro-particles in the furnace. The characterisation and optimisation of the device are also discussed. Ten consecutive firings of a 30-pg sample of Pb resulted in relative standard deviations (RSD) of 4% for peak-height and 1.6% for peak-area measurements. The absolute detection limit, determined by comparing the response obtained for a 3-µl sample of a 10 ng ml–1 Pb solution in 1% HNO3 with that obtained for blanks containing 1% HNO3 only, was 10 and 14 fg, for a dwell time of 10 µs, for peak area and peak height, respectively. The linear dynamic range for Pb extends over three orders of magnitude, from 300 fg to 300 pg.

Determination of germanium, arsenic, selenium, tin and antimony in complex samples by hydride generation-microwave-induced plasma atomic-emission spectrometry

This paper describes the utilisation of a semi-automatic hydride generation device coupled to a microwave-induced argon-helium plasma that is used with a 0.5-m monochromator for the analysis of germanium, arsenic, selenium, tin and antimony in several complex samples. Incorporated in the system are a condensation tube and a Chromosorb 102 column that are used to separate the analyte species from hydrogen evolved during the course of the generation reaction, and to separate the analytes from condensed contaminants that cause spectral background interferences.Results reported are standard recoveries and relative precision for germanium, arsenic, selenium, tin and antimony in whole blood and in enriched flour. Also reported are arsenic and antimony values for NBS orchard leaves. Results obtained on complex samples are compared with the precision obtained for aqueous standards.

Modification of a commercial electrothermal vaporisation system for inductively coupled plasma spectrometry: evaluation and matrix effects

The development and analytical utility of an electrothermal vaporisation technique (ETV) employing a Perkin-Elmer HGA-500 graphite furnace for sample introduction into the inductively coupled plasma (ICP) are assessed. Evaluation of a novel configuration with custom graphite cuvettes is described. Operational characteristics, including the effect of the length of the transport tube to the ICP torch, vaporisation temperature, carrier argon flow-rate, observation height above the coil and plasma power, are investigated. Detection limits for Be, Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn ranged from 0.6 to 20 ng ml–1 with precision varying from 1.2 to 8.5% RSD at 300 ng ml–1(3 µl). The effects of major biological matrix constituents (Ca, Fe, K, Mg, Na and P) on the determination of trace elements by ETV-ICP is also investigated. Significant enhancement and/or suppression of the analyte emission is observed.

Microwave-induced plasma coupled to a tantalum-strip vaporization assembly for trace element analysis.

This report describes a tantalum-strip assembly coupled to a microwave-induced plasma. Detection limits obtained for several elements by using the apparatus are given. A procedure using bomb decomposition and chelate extraction in conjunction with the tantalum-strip assembly/microwave-induced plasma system for the determination of trace elements in samples with complex matrices is also described. Recoveries from spiked standards are given.

Effect of ion-lens tuning and flow injection on non-spectroscopic matrix interferences in inductively coupled plasma mass spectrometry

The effects of various matrix constituents, Co, Pb and synthetic ocean water, on analyte signal have been studied. Suppression of the 138Ba+ signal was observed in the presence of each matrix, with the Pb matrix having the greatest effect. These matrix-induced suppressions of analyte signal were compensated for in part by the use of In as an internal standard, and by initially tuning the ion lenses for maximum analyte signal in the presence of the matrix, rather than for a simple acidified standard solution. The severity of matrix-induced suppression was compared for flow injection and continuous sample introduction. No significant differences in suppression of analyte signal between the two methods were observed because of the relatively large sample volume used for flow injection. The experimental procedure adopted, continual reference of analyte signals with and without the matrix present, effectively eliminated any bias in the results due to nebuliser and cone blockage.

Elemental mass spectrometry using a moderate power microwave-induced plasma as an ion source

A moderate power microwave-induced argon plasma operated at atmospheric pressure is evaluated as an ion source for mass spectrometry. Data are presented which illustrate a non-homogeneous distribution of the analyte ions throughout the plasma requiring sampling from a position where molecular oxide and hydroxide formation is favoured. Effects of sampling depth, plasma power and argon flow-rate on the ion signals are discussed. Major background ions present in the argon microwave induced plasma (Ar MIP) are similar to those encountered in the argon inductively coupled plasma (Ar ICP). Detection limits using this laboratory-built instrument, range from 7 to 70 ng ml–1 depending on the ionisation potential. The effects of concomitant elements are much more severe with the Ar MIP than with the Ar ICP using the same instrument.

Determination of polybrominated biphenyl and related compounds by gas-liquid chromatography with a plasma emission detector

Polybrominated biphenyl and related compounds were separated by gas-liquid chromatography and monitored by a microwave-induced plasma emission detector. The helium plasma was sustained at atmospheric pressure in a Beenakker cavity. By following the bromine emission at 478.55 nm, linear ranges of at least 103 with detection limits (signal to noise ratio = 3) of the order of 1 ng were achieved. These results are compared with those obtained with an electron-capture detector and the advantages of the element selectivity of the plasma system are illustrated.