Detection of Ultratrace Phosphorus and Sulfur by Quadrupole ICPMS with Dynamic Reaction Cell

Abstract

A method of detection of ultratrace phosphorus and sulfur that uses reaction with O2 in a dynamic reaction cell (DRC) to oxidize S+ and P+ to allow their detection as SO+ and PO+ is described. The method reduces the effect of polyatomic isobaric interferences at m/z = 31 and 32 by detecting P+ and S+ as the product oxide ions that are less interfered. Use of an axial field in the DRC improves transmission of the product oxide ions 4-6 times. With no axial field, detection limits (3sigma, 5-s integration) of 0.20 and 0.52 ng/mL, with background equivalent concentrations of 0.53 and 4.8 ng/mL, respectively, are achieved. At an optimum axial field potential (200 V), the detection limits are 0.06 ng/mL for P and 0.2 ng/mL for S, respectively. The method is used for determining the degree of phosphorylation of beta-casein, and regular and dephosphorylated alpha-caseins at 10-1000 fmol/microL concentration, with 5-10% v/v organic sample matrix (acetonitrile, formic acid, ammonium bicarbonate). The measured degree of phosphorylation for beta-casein (4.9 phosphorus atoms/molecule) and regular alpha-casein (8.8 phoshorus atoms/molecule) are in good agreement with the structural data for the proteins. The P/S ratio for regular alpha-casein (1.58) is in good agreement with the ratio of the number of phosphorylation sites to the number of sulfur-containing amino acid residues cysteine and methionine. The P/S ratio for commercially available dephosphorylated alpha-casein is measured at 0.41 (approximately 26% residual phosphate).

Quantification of Proteins by Measuring the Sulfur Content of Their Constituent Peptides by Means of Nano HPLC-ICPMS

“…The 32 S 16 O detection limit was similar to the detection limits obtained by using other hyphenated ICPMS techniques for S detection. 24,25 Also, the detection limit of 32 S under the Xe gas mode was also similar to previously reported values. 12,19 Taking into account the sample volume of 2.0 μL, in ICPMS under O2 gas mode the absolute detection limits for vasopressin, oxytocin, and amyloid β were 65, 77, and 110 fmol, respectively.…”

Sinais de fundo em análise instrumental: uma discussão essencial em cursos de graduação

“…A formação de um novo íon a ser monitorado também é possível, tal como exemplificado na determinação de S e P monitorando SO + e PO + , respectivamente. 42 Essas abordagens podem ser exploradas para a minimização do BG intrínseco à técnica, bem como para superar interferências.…”

Oxygenation Mechanism of Ions in Dynamic Reaction Cell ICP-MS

“…[30][31][32] Oxygenation is an effective way of avoiding spectral interferences by producing an oxide ion free from interfering molecular ions or by oxygenating the isobaric interfering ions. [33][34][35][36][37][38][39][40][41][42][43] However, the effectiveness of O2 has not been evaluated sufficiently and the underlying mechanism of oxygenation in the reaction cell has not been fully elucidated, although the mechanisms underlying the use of NH3 and CH4 have been discussed by several researchers. We investigated the mechanism of oxygenation by using the bond energy and the enthalpy change (ΔH) between the ions and O, and demonstrated the usefulness of theoretical calculations for elucidating reaction mechanisms in DRCs.…”