Alan L. Gray

Solid sample introduction by laser ablation for inductively coupled plasma source mass spectrometry

The results are described of a preliminary study of the mass spectrometry of solid samples using a ruby laser to ablate the sample into an inductively coupled plasma (ICP) source mass spectrometer. Standard rock samples were used, pelletted with a binder into the form of a disc. Some 200 ablation pits could be accommodated on each sample. Laser pulse energies of 0.3–1 J were used in the fixed Q mode and the ablated material transferred from the ablation cell into the plasma torch by means of the plasma injector gas flow. The mass spectrometer was used in the fixed ion mode using mean ion current detection to evaluate the reproducibility of successive pulses on major constituents and in the scanning mode at the rate of 10 scans s–1 to produce spectra using mean current detection for major elements and pulse counting detection for traces. Problems were experienced with saturation of the detection system in both the mean current and pulse counting modes owing to the transient nature of the sample pulse from the laser, when attempting to quantify major elements, but except where a major peak was saturated, reasonably uniform sensitivity for most elements across the mass range from 7 to 238 m/z was obtained. Isotope ratio measurements were made on lead at 29 µg g–1 and detection limits for the elements examined appear to be 10 ng g–1 or less.

Inductively coupled plasma source mass spectrometry using continuum flow ion extraction

An inorganic mass spectrometry system is described that uses an atmospheric pressure inductively coupled plasma (ICP) as an ion source. Solution samples may be introduced directly by nebulisation and the analysis time is about 1 min. Ions are extracted from the bulk plasma without any intervening boundary layer so that the full advantages of the ICP as a hightemperature dissociation and ionisation medium are realised.A quadrupole mass analyser is used with a pulse counting ion detector followed by a multi-channel scaler data system. General background levels are low and a wide range of elements may be determined with detection limits below 1 ng ml–1.Spectra are very simple with few molecular analyte ions and only singly and doubly charged species are found. Mass resolution is adequate to avoid peak overlap and isotope ratio determinations may readily be made with precision below 0.5%, with integration times of about 5 min.The operating characteristics and performance of the system are described and illustrated and the future development potential is discussed.

Plasma source mass spectrometry using an inductively coupled plasma and a high resolution quadrupole mass filter

The performance of an instrument using an inductively coupled plasma as an ion source with a high resolution mass filter to analyse the extracted ions is described. A description of the experimental system is given and the spectral characteristics of the technique are discussed. The current performance of the technique for simple solution analysis is described, and the future potential for trace element analysis and isotope ratio measurement is assessed.

The ICP as an ion source ― origins, achievements and prospects

Abstract The origins and development of the application of the ICP as an atmospheric pressure ion source for mass spectrometry are described and an outline of the technique as it is currently used for multi-element ultratrace analysis of solutions is given. Present achievements and limitations are discussed and the areas of likely development in the near future are outlined.

Determination of trace elements in geological samples by inductively coupled plasma source mass spectrometry

Abstract The application of inductively coupled plasma souice mass spectrometry (ICP-MS) to the determination of 27 trace elements in geological samples demonstrates the potential of this new analytical method. Data are presented for 13 trace elements in 3 international standard reference water samples, and 14 rare earth elements in 3 international standard reference silicate rocks.

Mass spectrometry with an inductively coupled plasma as an ion source: the influence on ultratrace analysis of background and matrix response

Abstract An outline is provided of the mode of operation of the atmospheric pressure inductively coupled plasma (ICP) when used as a mass spectrometer ion source. The generation of doubly charged ions and molecular peaks is discussed for the authors system in relation to the limitations they impose on trace element detection limits and on the analysis of samples with high matrix concentrations. Detection limits obtained under compromise operating conditions are shown for a range of elements in both single ion and multielement detection modes.

Progress in plasma source mass spectrometry

Abstract Development work in the application of the inductively coupled plasma to plasma source mass spectrometry is described. Two modes of operation are identified, boundary layer sampling and continuum (or bulk plasma) sampling. Boundary layer sampling is characterized by very high signal-to-background ratios, giving detection limits better than 1 ng ml −1 for a wide range of elements. The technique is applied to solution samples, nebulized at approximately 2.5 ml min −1 . Samples may be processed at a rate of one every few minutes. The performance of the technique under boundary layer sampling conditions is illustrated by the rapid determination of lead isotope ratios in galena samples. Boundary layer sampling suffers from several disadvantages, including salt condensation on the sampling aperture, significant inter-element effects, and complex spectra for elements forming strongly bound oxides. It is currently limited to the analysis of simple solution samples. In order to overcome these disadvantages, continuum sampling has been introduced. System performance is compared to that achieved with boundary layer sampling, and the future potential of the technique in both modes of operation is discussed.

Development progress in plasma source mass spectrometry

Development work in the application of the inductively coupled plasma to plasma source mass spectrometry is described. Preliminary results obtained under continuum (or bulk plasma) sampling conditions are illustrated and compared with previously published boundary layer sampling work. The technique is now shown to be viable for multi-element analysis of complex samples.

Inductively coupled plasma mass spectrometric determination of the absorption of iron in normal women

The determination of iron isotope ratios in blood, without prior sample preparation, using inductively coupled plasma mass spectrometry (ICP-MS) with sample introduction by electrothermal vaporisation (ETV) is described. Following oral administration of 5 mg of enriched 54FeSO4 and intravenous administration of 200 micrograms of 57FeSO4 to non-pregnant women, the 54Fe: 56Fe and 57Fe: 56Fe isotope ratios in serum were measured reliably within 20 min per sample in quintuplicate. Changes in the fractional absorption of iron during human pregnancy could therefore be assessed.

Noise in inductively coupled plasma mass spectrometry: some preliminary measurements

Fundamental limiting noise sources in a non-commercial inductively coupled plasma mass spectrometer were investigated, using colour photographic evidence and signal processing which is manipulated via computer software. Noise sources were found to be 50 Hz from the mains power supply, peristaltic pump rotation, plasma audiofrequency peaks and their harmonics, and 1/f noise (which is mainly caused by the sample introduction system). These noise sources adversely affect the precision of inductively coupled plasma mass spectrometry (ICP-MS) for a given measurement bandwidth. To reduce their contributions in the noise power spectra (NPS) of the signal, the use of a bonnet device was investigated. This reduced the 1/f noise and peristaltic pump rotation frequency and completely removed the plasma audio frequency peak in the NPS. This latter frequency has been observed by a number of workers in ICP emission spectrometry and is associated with instability at the boundary of the plasma, where it enters the surrounding atmosphere. This audiofrequency peak has been removed in emission spectrometry by using an extended torch arrangement. In this present work the position of the plasma audiofrequency peak in the NPS changed with sampling distance, radiofrequency power and coolant gas flow rate and the peak was removed by the use of a torch extension bonnet.