Abstract
Bismuth was evaluated as internal standard for Pb determinations and showed usefulness to minimize variations due to changes in the experimental conditions of the inductively coupled plasma optical emission spectrometry (ICP OES), inductively coupled plasma mass spectrometry (ICP-MS) and electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). Thirty four samples were analyzed and the Pb contents obtained by ICP-MS and ETV-ICP-MS were in agreement at 95% confidence level. Plant, biological tissue and soil reference materials were also analyzed and the results were close to certified values upon the use of the internal standard. Recoveries for Pb spikes (ICP OES: 95-110%; ICP-MS: 95-106%; ETV-ICP-MS: 92-119%) were better than those obtained with external calibration (ICP OES: 56-91%; ICP-MS: 36-136%; ETV‑ICP-MS: 5-123%). The relative standard deviations (n = 12) was improved from 1-9% to 0.2-6% (ICP OES), from 0.5-11% to 0.1-7% (ICP-MS) and from 0.4-7% to 0.1-4% (ETV‑ICP‑MS) by using external and internal standard calibrations, respectively.
Highlights
Internal standard (IS) technique is a simple, effective and well-established calibration method to compensate for a wide range of interferences, as matrix effects.[1]
All samples and certified reference materials (CRM) were prepared in triplicate and spiked with 200 μg L-1 Bi (ICP OES), 1.0 μg L-1 Bi (ICP‐MS) and 10 μg L-1 Bi (ETV-inductively coupled plasma mass spectrometry (ICP-MS))
With the radio frequency (RF) power fixed at 1.25 kW, the nebulizer gas flow rate was varied between 0.7-1.1 L min-1, after the nebulizer gas flow rate was fixed at 0.9 L min-1 and the RF power was ranged from 0.9 to 1.25 kW
Summary
Internal standard (IS) technique is a simple, effective and well-established calibration method to compensate for a wide range of interferences, as matrix effects.[1] After the first proposal of IS in flame emission spectrometry,[2] it has been currently used with inductively coupled plasma mass spectrometry (ICP-MS)[3] and inductively coupled plasma optical emission spectrometry (ICP OES).[4]. The effectiveness of using IS on analytical accuracy and precision depends on the choice of an adequate internal standard. Some parameters are important to select an internal standard for ICP-based techniques. For ICP OES, the main criteria are similar excitation energies for IS and analyte, appropriated plasma operation conditions (radio-frequency power and nebulizer gas flow rate), absence of spectral interferences between analyte and IS emission lines and absence of the IS in the sample.[5,6,7] In ICP-MS, the selection parameters for the IS
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