Analysis of Potable and Wastewaters Using An Autodilution/Calibration System and ICP-OES

In 1970, the United States government established the Environmental Protection Agency (EPA) in response to growing public demand for a cleaner environment. The Agency was not only given the responsibility for setting national standards, but also for issuing permits and monitoring compliance at the state and local government level. Where national standards were not met, the U.S. EPA could take steps to enforce local government in reaching the desired levels of environmental quality.

The Safe Drinking Water Act (SDWA) is the main federal law that ensures the quality of drinking water in the U.S. Under SDWA, the U.S. EPA sets standards for drinking water quality and oversees the states, localities, and water suppliers that implement those standards. SDWA was originally passed by Congress in 1974 to protect public health by regulating the nation’s public drinking water supplies. The law was amended in 1986 and 1996 and was mandated to safeguard drinking water and its sources such as rivers, lakes, reservoirs, springs, and natural ground waters.

The U.S. EPA’s Office of Ground Water and Drinking Water (OGWDW) administers control under Federal Regulation 40 CFR Part 141. This regulation states that all drinking water supplies must comply with the Maximum Contaminant Levels (MCLs) for the major contaminants specified in the National Primary Drinking Water Regulations (NPDWRs). Additional, less toxic contaminants are given target maximum values set by the National Secondary Drinking Water Regulations (NSDWRs) (40 CFR Part 143).

The approved method for the determination of metallic contaminants for compliance measurements by inductively coupled plasma-optical emission spectrometry (ICP-OES) is U.S. EPA Method 200.7, “Determination of Metals and Trace Elements in Water and Wastes by Inductively Coupled Plasma-Atomic Emission Spectrometry.” It was first published in 1982 and went through four major revisions before the method was finalized in 1994. Method 200.7, Version 4.4,1 has not changed in almost 20 years and covers the use of radial or axial ICP-OES for the determination of 31 metals and some nonmetals in potable waters and wastewaters for regulatory compliance. This method contains a lengthy description of procedures for the collection, preservation, preparation, and analysis of samples.

Inductively coupled plasma-optical emission spectrometry and autodilution/calibration

The objective of this study was to follow Method 200.7 using an Optima 8300 ICP-OES (PerkinElmer, Shelton, CT) coupled with the prepFAST™ automated autodilution/calibration system (Elemental Scientific [ESI], Omaha, NE). The prepFAST system provides a number of advantages over conventional ICP-OES introduction systems, the most significant being higher sample throughput and reduced memory effects. The system allows accurate, syringe-driven autodilution of samples and standards, eliminating manual dilution errors and increasing calibration range. By reducing consumption of the sample and high-purity chemical reagents, the prepFAST is one of the most cost-effective ways to improve laboratory productivity.2

Experimental

To be compliant with U.S. EPA Method 200.7, a number of quality checks must be completed before sample analysis to ensure the instrument is working to its maximum potential. Some of these tests include instrument tuning; calibration; performance checks, including interelement correction (IEC); instrument detection limits (IDLs); method detection limits (MDLs); quality control (QC) samples; linear dynamic range (LDR); method blanks; and spike recoveries.

The instrument was set up with the operating conditions shown in Table 1 using the recommended wavelengths and background correction points described in the method. For some analytes, multiple wavelengths were used, based on sensitivity and/or freedom from interference. It should also be emphasized that a plasma flow rate of 8 L/min was used for this analysis, which is typically 50% lower than other ICP-OES systems.

Table 1 – ICP-OES operating conditions used in this study

Calibration

The majority of solutions prepared for this study were diluted in 2% nitric acid. For calibration, a 1-mg/L standard and a 5-mg/L standard were prepared, and the prepFAST system was used to automatically dilute these solutions to further prepare other calibration standards and blanks. The system was also configured to automatically dilute samples, some of which were deliberately prepared over the range of the calibration curve, so that it would automatically perform a sample dilution. Yttrium was used as the internal standard for the analysis of all samples.

Results

To exemplify the detection capability of the system used in the study, Method 200.7 IDLs and MDLs of all the analytes were carried out. These are shown in Table 2. To emphasize the accuracy of the dilutions done by the prepFAST, Table 3 shows sample analysis data for the recovery of the Analyte B solution (referenced to a 10× user-prepared dilution) with further prepFAST dilutions at 10× or 100×, when necessary. It can be seen that the recoveries of all analytes are well within the U.S. EPA guidelines of 85–115%. For the complete set of sample results generated in this study, please refer to the published reference.3

Table 2 – Detection limits achieved in this study using U.S. EPA Method 200.7 parameters
Table 3 – Recovery of the Analyte B solution run as a sample in duplicate (referenced to a 10× user-prepared dilution) with a further 10× prepFAST dilution

Conclusion

This study has demonstrated the capabilities of the Optima 8300 ICP-OES coupled with the prepFAST autodilution/calibration system to produce results that meet the rigorous requirements outlined in U.S. EPA Method 200.7 for the analysis of potable and wastewaters. The detection limits demonstrate that the system is capable of easily meeting the National Primary and Secondary Drinking Water Maximum Contaminant Levels, even for elements like antimony, arsenic, and thallium, which have traditionally been determined by heated graphite furnace (HGA) or ICP-MS. The accuracy and precision of the Optima 8300 allow users to spend less time on the performance requirements, while the prepFAST simplifies sample preparation, allowing higher sample throughput while reducing memory effects and minimizing errors and contamination.

References

  1. U.S. EPA Method 200.7, Rev. 4.4. Determination of Metals and Trace Elements in Water and Wastes by Inductively Coupled Plasma-Atomic Emission Spectrometry; http:// water.epa.gov/scitech/methods/cwa/bioindicators/ upload/2007_07_10_methods_ method_200_7.pdf; 1994.
  2. http://www.icpms.com/products/prepfast.php; 2013.
  3. Bradshaw, D.K.; Thompson, L. The Analysis of Water and Wastes by U.S. EPA Method 200.7 Using the Optima 8300 ICP-OES and prepFAST Auto-Dilution/Calibration System; http://www.perkinelmer.com/CMSResources/ Images/44-153346APP_Optima- 8300-prepFAST-US-EPA-200.pdf; 2013.

Laura Thompson is ICP-OES Product Manager, PerkinElmer, 710 Bridgeport Ave., Shelton, CT 06484, U.S.A.; tel.: 203-925-4602; e-mail: Laura.Thompson@perkinelmer.com; www.perkinelmer.com.

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