Understanding instrumental analysis is essential for obtaining reliable analytical results required by chemists in a variety of research areas and industrial activities. All instrumental techniques involve undesirable background (BG) signals originated either from concomitants in the sample or by spurious (e.g. electrical or optical) effects intrinsically related to the measurement process. BG signals may affect accuracy, precision and detection limits. Techniques characterized by low BG stands out by high detectability even when they are based on processes with low efficiency (e.g. low quantum yields and low efficiency of thermal excitation). However, minor attention has been given to this topic in analytical chemistry courses hindering students' understanding of the BG concept and its impact on the analytical performance. Although in some analytical techniques BG is well-defined and successfully compensated, some of them still need further elucidation. Sources of BG and strategies for its minimization and correction are didactically discussed for a variety of analytical techniques, including molecular and atomic spectrometry, electroanalytical methods, and separation techniques. Historical aspects and recent approaches are also addressed.

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.