Flow-Injection Hydride Generation AAS

What is the Flow-Injection Hydride Generation AAS?

A flow-injection hydride generation AAS injects discrete sample plugs into a flowing reagent stream. It is chosen when reagent economy, fast transient signals and low sample consumption are important in routine arsenic and selenium testing.

Overview

Flow injection introduces a small, precisely measured sample plug into a continuously flowing acid and reductant carrier. The reaction zone is dispersed as it travels to the gas-liquid separator, producing a transient hydride peak that is recorded and integrated. Reagent consumption is much lower than in continuous flow because reductant flows while sample is injected, and sample volume can be as little as 100 to 500 microlitres. The short residence time suits elements that react quickly and allows rapid repeat injections for signal averaging. Peak height or area is calibrated, and the technique adapts easily to on-line preconcentration, dilution or standard addition by adding valves and loops. Setup is more complex than continuous flow, and timing and dispersion must be optimized, but the approach is valued where reagents are costly or samples are scarce.

How does it work?

The sample is mixed with acid and sodium borohydride, which reduces the analyte to a volatile covalent hydride such as arsine or selenide. A carrier gas sweeps the hydride into a heated quartz tube or a small flame, where it decomposes into free atoms. The atoms absorb light from an element-specific hollow-cathode lamp, and absorbance follows the Beer-Lambert law. Because the hydride is separated from the liquid matrix before atomization, most interferents remain behind, which gives high sensitivity and low background. Mercury can be determined by cold vapor generation without heating because it is already volatile. Reaction conditions such as acid type and concentration, borohydride concentration, flow rates and reaction temperature must be tightly controlled, and interfering ions such as copper and nickel are masked or removed. Calibration uses aqueous standards treated in the same way as samples.

What are the key features?

• Precise injection valve with sample loop
• Low reagent and sample consumption
• Transient peak integration for calibration
• Rapid repeat injections for signal averaging
• Optional on-line preconcentration and dilution
• Compact manifold for hydride generation

What are the technical specifications?

A typical flow-injection hydride generation aas configuration offers elements of As, Se, Sb, Bi, Sn, Te, sample volume of 100–500 µL, detection limit of 0.03–0.3 µg/L, carrier gas of argon or nitrogen, 100–300 mL/min, quartz cell temperature of 800–900 °C and reductant of 0.1–1% sodium borohydride. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Flow-Injection Hydride Generation AAS is used in trace arsenic and selenium in limited samples, selenium speciation after chromatographic separation, environmental samples with on-line preconcentration and clinical and biological trace element analysis. Across the wider Hydride Generation AAS class, laboratories also deploy it for arsenic and selenium in drinking water, arsenic and mercury in rice, fish and seafood and antimony and tin in packaging material migration.

Which standards and certifications apply?

Relevant standards and methods include Ph. Eur. 2.2.22 Atomic absorption spectrometry, USP <852> Atomic Absorption Spectroscopy, ISO 11969 Water quality — Determination of arsenic by AAS, US EPA Method 7062 Arsenic by hydride generation, US EPA Method 7473 Mercury in solids and solutions and IEC 61010-1. Certification candidates for this model are CE, ISO 9001 manufacturing and IEC 61010-1 safety compliance; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Hydride generation uses sodium borohydride solutions that must be prepared fresh or kept cooled, and reactions can release hydrogen gas, so ventilation is required. Acid and reductant concentrations, tubing lengths and gas flows affect the yield and must be fixed in the method. Interfering elements are controlled with masking agents such as thiourea or by separation. Quartz cells cloud with use and need periodic cleaning or replacement, and their temperature affects atomization efficiency. Because the technique measures a transient or steady signal from a gas, blank contamination from reagents is a common problem; ultrapure reagents and method blanks are essential. Install the system on the flame or furnace instrument with the correct gas supply and waste handling.

How do I select the right Flow-Injection Hydride Generation AAS?

Select the flow-injection variant when samples are scarce, reagents are expensive or on-line preconcentration and speciation are planned. Specify the elements, sample volume available and whether a column or separation interface will be connected. Confirm that peak integration settings are validated for the dispersion produced by your manifold.

How does it compare with other Hydride Generation AAS variants?

Choose a hydride generation system when the target elements are arsenic, selenium, antimony, bismuth, tin, tellurium or mercury and detection limits around 0.01 to 0.5 micrograms per litre are required at moderate cost. Continuous-flow designs offer stable signals and good throughput, flow-injection designs use less reagent and allow fast transient measurements, and batch systems are cheapest but slowest. If mercury is also required, add a cold vapor module or select an instrument with both modes. Multi-element configurations reduce time when several hydride-forming elements are measured together. For very low detection limits on arsenic and selenium, compare with ICP-MS, which may offer lower limits at higher cost.