AWWA WQTC62366

This paper describes an at-line arsenic monitor with comparable (or better) performance to established US Environmental Protection Agency (USEPA) approved methods called the TraceDetect SafeGuard™ with Nano-Ban™ technology. The SafeGuard instrument is presently configured to measure total arsenic in the 1 ¿¿¿¿¿¿¿¿ 50 ppb range (for drinking water applications) or in the 50 ¿¿¿¿¿¿¿¿ 500 ppb range for industrial wastewater applications. Water utilities can use this monitor to ensure compliance, to adjust their treatment chemistry, to prevent "break-through" in the treatment system, and to monitor the ion-exchange regeneration system. This self-contained instrument requires only 120 VAC power, compressed nitrogen and comes with a PC to control and record test data. Reagents are replaced monthly. This instrument combines a novel sample pretreatment system with Sequential Injection Analysis (SIA) and Anodic Stripping Voltammetry (ASV) performed with a patented Nano-Band™ Electrode sensor. This is a unique technology developed by TraceDetect and used in a successful line of manual analysis instruments. The SafeGuard instrument automates the ASV measurement, performing sample treatment, and a full measurement via standard additions in 30 minutes. The result is accurate to 20% or 1 ppb in the range of 1 ¿¿¿¿¿¿¿¿ 50 ppb total arsenic. A single measurement proceeds as follows. The sample is loaded into Preparation Module and acidified. If required, the sample is also diluted at this point. If a measurement of As(III) is desired, the sample is moved immediately to the Test Cell and measured. The measurement produces a peak for arsenic in a voltammogram: peak height is proportional to the As(III) concentration. After the initial measurement, standard additions are made to the test cell and the measurement is repeated after each addition. A calibration curve is constructed and used to calculate the concentration of the original sample. Matrix effects and sensor drift are automatically accounted for in this method. If a measurement of total arsenic is desired, the sample is pretreated with a reducing agent before moving to the Test Cell. The reducing agent is selected such that all As(V) is converted to As(III) but not further reduced. The measurement then proceeds as outlined above. The data collected during the measurement allows the instrument to monitor data quality and sensor performance. The controlling software uses this to alert the user should the sensor need to be cleaned and regenerated. Sensor cleaning is a manual process that takes 3 minutes. After cleaning, the sensor's gold film is replaced: this latter step is performed in the SafeGuard unit under software control and takes 20 minutes. After regeneration, the sensor's performance is verified before measurements continue. Data collected in the field on an industrial waste stream indicates that sensor regeneration is required every 3 to 7 days, depending on use. The SafeGuard unit is adaptable to other sample streams. If organic arsenic is present, the pretreatment module can be programmed to inject oxidizer into the sample. This frees the organically bound arsenic and converts it to As(V). Subsequent addition of the reducing agent then converts the arsenic to the measurable form, As(III), prior to analysis. If the sample stream contains a significant amount of copper (not typical in ground water but a common contaminant due to plumbing fixtures), a ion-selective adsorption cartridge can be added that removes 99% of the copper, but passes the As(III) and As(V). Includes tables, figures.