Flow-injection atomic spectrometry: a new analytical technique

Simple multi-signal calibrations exploiting flow analysis systems

Multi-signal calibrations have been recently exploited in molecular spectrochemical analysis alternatively to traditional calibration methods, improving analytical frequency and accuracy. The application of these strategies is simple and minimizes efficiently matrix effects by analyzing two calibration solutions comprising sample plus standard (S1), and sample plus blank (S2). The plot of the signals obtained with S1 and S2 at multiple settings (e.g. different wavelengths) yield a slope that can be related to the analyte concentration in the sample. Similarly, transient signals could also be related to the analyte concentration exploiting a similar strategy. Thus, in this work, two multi-signal approaches developed in flow-based systems are proposed, based on the responses at multiple wavelengths (online multi-energy calibration, OMEC), and on the dispersion profile of the samples, herein denominated multi-dispersion calibration (MDC). The calibrations were carried out with sample solutions after 2-fold dilution with a standard solution and with water. The feasibility of OMEC and MDC were demonstrated using KMnO4 solutions (without chemical reactions) under continuous and pulsed flow regimes. The applicability of this strategy was also demonstrated by the spectrophotometric determination of urea in milk and pet potty spray in a multi-pumping flow system, based on the color change of bromothymol blue after catalyzed hydrolysis by urease from jack beans (Canavalia ensiformis). MDC and OMEC were compared with external calibrations (EC) and classical standard addition. The limits of detection for urea were estimated at 13 mg L-1, 16 mg L-1, and 10 mg L-1 using MDC, MEC and EC, respectively. Recoveries from 93 to 101%, and the agreement of sample analyzes with the reference procedure demonstrated the good accuracy achieved by the proposed methods. Therefore, it was demonstrated the feasibility of MDC and OMEC for analytical purposes in a simple and efficient way with the advantages of flow-based manifolds.

Flow injection on-line dilution for zinc determination in human saliva with electrothermal atomic absorption spectrometry detection

An automated method is described for the determination of zinc in human saliva by electrothermal atomic absorption spectrometry (ET AAS) after on-line dilution of samples with a significant reduction of sample consumption per analysis (<0.4 mL including the dead volume of the system). In order to fulfill this aim without changing the sample transport conduits during the experiments, a flow injection (FI) dilution system was constructed. Its principal parts are: one propulsion device (peristaltic pump, PP) for either samples, standards or washing solution all located in an autosampler tray and for the surfactant solution (Triton X-100) used as diluent, and a two-position time based solenoid injector (TBSI(1)) which allowed the introduction of 10 microL of either solution in the diluent stream. To avoid unnecessary waste of samples, the TBSI(1) also permitted the recirculation of the solutions to their respective autosampler cups. The downstream diluted solution fills a home made sampling arm assembly. The sequential deposition of 20 microL aliquots of samples or standards on the graphite tube platform was carried out by air displacement with a similar time based solenoid injector (TBSI(2)). The dilution procedure and the injection of solutions into the atomizer are computer controlled and synchronized with the operation of the temperature program. Samples or standards solutions were submitted to two drying steps (at 90 and 130 degrees C), followed by pyrolysis and atomization at 700 and 1700 degrees C, respectively. The aqueous calibration was linear up to 120.0 microgL(-1) for diluted standard solutions/samples and its slope was similar (p>0.05) to the standard addition curve, indicating lack of matrix effect. The precision tested by repeated analysis of real saliva samples was less than 3% and the detection limit (3sigma) was of 0.35 microgL(-1). To test the accuracy of the proposed procedure, recovery tests were performed, obtaining mean recovery of added zinc of 97.8+/-1.3%. Furthermore, Zn values estimated by the procedure developed in this work were compared with those obtained by a standard addition flame-AAS method applied to 20 randomly selected saliva samples. No significant differences (p>0.05) were obtained between the two methods. Zinc levels in saliva samples from 44 healthy volunteers, 15 male and 29 female, with ages between 20 and 51 years (mean 30.50+/-9.14 years) were in the range 22-98 microgL(-1) (mean of 55+/-17 microgL(-1)), similar to some and different from others reported in the literature. It was found that zinc values for male were statistically higher (p=0.006) than for female.

Novel multichannel plasma-source mass spectrometer

A novel mass spectrometer system for elemental analysis is described. The instrument combines an inductively coupled plasma (ICP) ion source with a Mattauch-Herzog mass spectrometer and multichannel ion detector. Ion detection is simultaneous and an elemental mass spectrum (20-230 μ) can be acquired in <10 ms. The instrument can be used with either Ar or He plasma sources. The speed of the system makes it well suited for acquisition of fast (10-100-ms duration) transient signals, such as those generated by pulsed laser ablation sample introduction. Preliminary system performance characteristics, which include detection limits, stability, and measurement accuracy, obtained with an Ar ICP are presented. The application of the instrument to the analysis of solid samples by laser ablation is discussed.