Multi-flow calibration (MFC) is based on monitoring the analytical signal from a single calibration standard solution at several different nebulization gas flow rates (Q), which normalizes plasma conditions and minimizes matrix effects. In the present study, MFC was evaluated, for the first time, applied to inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS) to analyze different and complex-matrix samples. Al, As, Cd, Cr, Cu, Mn, Pb, and Zn were determined by ICP OES, while As, Cd, Co, Cu, Hg, Mo, Mn, Ni, Se, Sb, Pb, and V were determined by ICP-MS. MFC results were compared with those obtained using external standard calibration (EC) for both techniques and in all cases, MFC showed equal or superior accuracy (recoveries between 80-120%) compared to EC, and lower relative standard deviation (RSDs ≤ 10%). Several tests were also performed using only two nebulization gas flows to build linear models for calibration (called two-flow calibration, TFC) and the accurate results (recoveries ranged from 80 to 110% for ICP OES and from 81 to 102% for ICP-MS) suggests that this strategy can be also applied, resulting in a method with high sample throughput.

Drinking water samples taken from cafeteria sinks and water fountains in each of the 76 schools in the Winston-Salem/Forsyth County Schools (WSFCS) district (North Carolina, United States) were analyzed by inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) to determine As, Cd, Cr, Cu, Pb, Sb, Se and Tl. All samples from currently active schools tested below the maximum contaminant level (MCL) set for each element. Model-based clustering was employed to identify schools more prone to drinking water contamination. This multivariate approach may be used in a prevention program that can be tailored to specific school districts, with each school tested at a frequency compatible with its contamination risk level. Water flow stagnation during the summer break results in higher elemental concentrations in school drinking water, but a simple 5-60 min flushing procedure significantly reduces the contamination levels.

A determinação de enxofre por espectrometria de massa com plasma acoplado indutivamente (ICP-MS) não é trivial, especialmente devido a intensas interferências espectrais causadas por íons poliatômicos como 16O2+, (16OH)2+, 14N16OH2+ e 14N18O+. Neste trabalho, espécies de argônio naturalmente presentes no plasma (padrões de interferência, IFS) são usadas para minimizar interferências espectrais na determinação de enxofre em microemulsões de biodiesel. Um método de calibração externa utilizando as razões entre os sinais analíticos e dos IFS é empregado em todas as determinações. Os limites de detecção (LOD) calculados para as razões 32/36, 34/36, 34/37 e 34/38 foram 4,0, 1,0, 1,0 e 0,8 mg L-1, respectivamente. Um material de referência certificado (Lubricating Oil, SRM 1848) e testes de adição e recuperação em amostras de biodiesel foram empregados para avaliar a exatidão do método. As recuperações variaram de 77 a 105% a partir do emprego de qualquer espécie IFS (36Ar+, 36ArH+ ou 38Ar+).

Determining sulfur by inductively coupled plasma mass spectrometry (ICP-MS) is not a trivial task especially due to the intense spectral interferences caused by polyatomic ions such as 16O2+, (16OH)2+, 14N16OH2+ and 14N18O+. In this work, argon species naturally present in the plasma (interference standards, IFS) are used to minimize spectral interferences on sulfur determination in biodiesel microemulsions. An external calibration method using ratios between analytical and IFS signals is employed in all determinations. The limits of detection (LOD) calculated for the 32/36, 34/36, 34/37 and 34/38 signal ratios were 4.0, 1.0, 1.0 and 0.8 mg L-1, respectively. A standard reference material (Lubricating Oil, SRM 1848) and spiking studies in biodiesel samples were employed to check the method accuracy. Recoveries varied from 77 to 105% while using any of the IFS probes (36Ar+, 36ArH+ or 38Ar+).

A interface de colisão e reação com He introduzido pelo skimmer a 100 mL min-1 é empregada para melhorar a exatidão na determinação de 31P+ por ICP-QMS. A determinação de 31P16O+ em plasma frio resulta em limites de detecção 55 vezes menores. Essa é uma alternativa interessante para elementos com altos potenciais de ionização como o P.

The collision/reaction interface with He introduced through the skimmer at 100 mL min-1 is employed to improve accuracy in 31P+ determinations by ICP-QMS. The 31P16O+ determination in cool plasma conditions result in limits of detection 55-fold lower. This strategy may be an interesting alternative for high ionization potential elements such as P.