Continuous-Flow Hydride Generation AAS

What is the Continuous-Flow Hydride Generation AAS?

A continuous-flow hydride generation AAS mixes sample, acid and reductant continuously and feeds a steady hydride stream to the atomizer. It is the standard choice for routine, high-throughput arsenic and selenium testing.

Overview

In this configuration a peristaltic pump delivers sample, hydrochloric acid and sodium borohydride through a mixing coil at constant rates. The reaction produces hydride continuously, and a gas-liquid separator strips the hydride into an argon or nitrogen carrier stream that flows to a heated quartz tube. Because the reaction reaches steady state, the absorbance signal is a plateau rather than a transient peak, which gives excellent precision and simple integration. Acid and reductant concentrations, flow rates and tube lengths are fixed during method development. The steady signal also allows signal-to-noise to be improved by extending measurement time. Carry-over is limited by an automatic rinse between samples. Typical detection limits are 0.05 to 0.5 micrograms per litre for arsenic and selenium, and throughput is 60 to 120 determinations per hour.

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?

• Peristaltic pump for sample, acid and reductant
• Mixing coil and gas-liquid separator
• Heated quartz tube atomizer with argon carrier
• Steady-state signal for high precision
• Automatic rinse between samples
• Throughput of 60 to 120 determinations per hour

What are the technical specifications?

A typical continuous-flow hydride generation aas configuration offers elements of As, Se, Sb, Bi, Sn, Te, detection limit of 0.05–0.5 µg/L, carrier gas of argon or nitrogen, 200–400 mL/min, quartz cell temperature of 800–900 °C, reductant of 0.5–2% sodium borohydride and acid of 1–5 mol/L hydrochloric acid. 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 Continuous-Flow Hydride Generation AAS is used in arsenic in drinking water and groundwater, selenium in food and feed, arsenic and antimony in soil and routine environmental compliance testing. 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 Continuous-Flow Hydride Generation AAS?

Select the continuous-flow variant for routine laboratories that measure hydride-forming elements frequently and value stable signals and high throughput. Specify the elements, concentration ranges and matrices, and confirm that the gas handling and ventilation suit borohydride reactions. Reserve changes of acid and reductant concentration for method development.

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.