Automated On-Line Isotope Dilution Analysis with ICP-MS Using Sandwich Flow Injection

Abstract

An automated flow injection (FI) manifold is described to perform the addition of isotopic spikes to aqueous samples on-line with ICP-MS for isotope dilution (ID) analysis. The manifold uses the sandwich technique (with the nested loop approach) to perform an injection of the isotopic spike solution within a sample (or standard) plug, the resulting sample-spike-sample sequence being pushed toward the nebulizer by a 1% HNO(3) carrier. A standard, which must contain one element not present in the spike solution to allow the determination of the dispersion coefficient, must also be used to allow a reverse isotope dilution analysis, as well as corrections for mass discrimination and/or spectroscopic interferences. Indeed, because the signals from the individual isotopes are monitored continuously, only one isotope free of spectroscopic interference is required for elements whose isotopic distribution does not vary in nature (two isotopes are still needed for the other elements), as a correction for the interference can be made by comparison with the signals from the standard. Furthermore, this automated approach makes ID-ICP-MS a faster method and does not require any preliminary analysis of the sample because the concentration profile resulting from FI allows the selection of the best isotopic ratio. It was successfully applied to the determination of Mo in saline water.

Atomic Spectrometry Update–Atomic mass spectrometry

“…Analyte recovery from the RM or standard with an enriched Mo isotope spike. 184 In both cases, sample and standard were injected in sequence, and NASS-4 was 90-110% and reproducibility better than 10% RSD. Sample throughput was better than 20 samples h−1 and dispersion was calculated using the spiked standard.…”

Online isotope dilution and inductively coupled plasma mass spectrometry: from elemental to species quantification

“…31 To reduce the high sample consumption of r-FI, an automated manifold to perform the sandwich flow injection system was proposed for online ICP-IDMS. 32 The spike solution was intercalated between two sample plugs as shown in Figure 2, which created a concentration gradient in the superposed profile of the analyte in the sample-spikesample sequence. However, in the r-FI and the sandwich flow approaches a point-by-point isotope ratio needs to be computed, eventually corrected and calculated using a modified ID equation.…”

“…The occurrence of sulfur in several amino-acids, peptides and metallothioneins makes it a key element for quantitative proteomic analysis by ICP-IDMS. ICP-SFMS at medium resolution or ICP-QMS with the technology of collision cells was employed to measure sulfur isotopes 32 S and 34 S which suffer strong interferences in low resolution mass spectrometers. 88 Sulfur has been the choice in quantitative proteomic analysis because it is present in several proteins and easily label metals and metalloids.…”

Inductively coupled plasma mass spectrometry in separation techniques: Recent trends in phosphorus speciation

“…Inductively coupled plasma-MS (ICP-MS) has become the detector of choice for online or offline element-specific detection of trace amounts of elements in complex matrices in recent years. Linearity over a wide dynamic range, high specificity and sensitivity, multielement detection capability, ability to perform isotopic analysis, and detector response irrespective of the chemical form of the species are some of the advantages, which make ICP-MS a better choice than conventional methods of detection when performing trace-element speciation in complex matrices [3,4].…”