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Nebraska DHHS Public Health Environmental Laboratory Upgrades Their Carbamate Water Testing
by James L. Balk, Ph.D., Chemist, Nebraska DHHS Public Health Environmental Laboratory
Introduction
Dr. James L. Balk at the Nebraska DHHS Public Health Environmental Laboratory. |
The Nebraska DHHS Public Health Environmental Laboratory conducts environmental testing for the state of Nebraska. It employs mandated U.S. Environmental Protection Agency (EPA) methods for the determination of regulated substances such as carbamates in drinking water. The drinking water program division has to ensure that drinking water is safe and meets detection limit criteria. The laboratory employs certified EPA Methods to determine if contamination levels exceed regulated maximum contamination levels (MCLs). These methods are designed to detect the stated drinking water contaminants within the specified detection limits published in the Federal Register. All procedures are conducted under compliance requirements with audit tracking. Typical analyses conducted by Nebraska DHHS Public Health Environmental Laboratory include diquat and paraquat (USEPA Method 549.2), Roundup, a glyphosate in drinking water, (EPA Method 547) and carbamate (EPA Method 531.1.). The optimized Pickering carbamate analytical system that includes analytical column, post-column derivatization (PCD) instrument and reagents, allows one to detect a spectrum of carbamates at ppb (μg/L) levels in drinking water. An Agilent 1100 HPLC interfaced with a Pickering Pinnacle PCX post-column derivatization system was used for this study.
Pinnacle PCX Evaluation
Background
The Pinnacle PCX is the third generation of Pickering PCD instruments that has been used in this laboratory. Initially, we worked with the PCX 5100, which eventually was replaced by the PCX 5200, its successor, an instrument that has provided excellent performance for a 5-year period.
Overview of the Pinnacle PCX Technology
There are some obvious hardware differences between the new Pinnacle PCX and its predecessor, the PCX 5200. For one, the older system is equipped with a reciprocating pump that uses check valves while the new system uses a syringe pump. The syringe pump delivers true pulse-free flow, so there is no need for pulse-dampening components that were part of the PCX5200. The new system design also provides easier access to hardware components. As a result, changing the reaction coil is facilitated, which is helpful when changing methods. This was not the case with the older system, which required removal of the front panels in order to gain access to these components.
System programming improvements in the Pinnacle PCX are also evident (i.e. in switching from a carbamate to a glyphosate analysis). The Pinnacle PCX syringe pump provides the capability for a piston actuated wash/reagent flush. This is conveniently performed, and the method can be set up in software to accomplish this. The Pinnacle PCX is also equipped with a column convection oven that makes rapidly cooling the column easier. Thus, in switching from carbamate to Glyphosate methods, the column temperature can be rapidly equilibrated, which translates to an improvement in throughput. Moreover, cooling and system flush are carried out simultaneously, further decreasing the switching interval between carrying out the two types of PCD analyses on this system. Another benefit attributed to the new syringe pump is conservation of reagent, i.e. when the column is equilibrating, it is not pumping reagent. This is a significant issue as, in addition to the cost saving, the disposal of toxic reagent materials can be problematic, and the opportunity to minimize the size of toxic waste is a welcome result.
Analysis/Conditions/Reagents
While the laboratory could make up its own reagents, the carbamate reagents used for Pinnacle PCX analyses conducted were purchased from the instrument manufacturer. One of the attractive features about the proprietary reagents is the fact that they are packaged with lot numbers and expiration dates. This makes them especially useful for audits as they are certified for the application, i.e. carbamate. In principle, one can use any column that meets the test requirements. Again, the proprietary columns provide an advantage in that they are optimized for the specific analytical application, and this saves time as there is no need to adjust the gradient program.
System Performance
Certain basic approaches are systematically applied in evaluating analytical equipment. Accordingly, the system was challenged to evaluate the linearity of the calibration curve to ensure a sufficient performance quality and to verify it meets specifications. In that regard, the Pinnacle PCX meets the EPA detection limits for drinking water. Beyond this benchmark, the capability to exceed these specifications would depend on the total system including the detector.
| A. ALDICARB SULFOXIDE – 0.2 mg/L LLLFB QC CHART |
B. ALDICARB SULFOXIDE – 2.0 mg/L LLFB QC CHART |
| Figure 1. Pinnacle PCX typical quality control charts for 0.2 mg/L and 2.0 mg/L Carbamate sample concentrations. |
Carbamate concentrations can be quantitated at 0.2 μg/L for the carbamate procedure.* Each time we run a procedure, we test below the lowest standards—a kind of quality control of the maximum detection limit (detection near the MDL). It is obvious that at this level the sensitivity has to be extraordinary for carbamates. While the lowest concentration calibration standard is 0.5 μg/L, we can get good quality control in terms of precision, that is, accurate results at 0.2 μg/L and 0.4 μg/L. Typical QC charts (Figure 1A) indicate some scatter in these measurements, but the precision is quite respectable considering the concentration. Obviously the precision will not be as good at a fortification level of 0.2 μg/L and 0.4 μg/L as at 2 μg/L (Figure 1B) or 5 μg/L. Below 0.2 μg/L, one might say that if the scatter is reflective of variation in actual sample concentration and not in instrument sensitivity, then sensitivity actually approaches 0.1 μg/L (Figure 1A). However, this is an observational extrapolation and not a verified determination. It must be remembered that at the limit of detection, small day-to-day variations in instrument tuning, baseline noise, etc., are consequential. In any case, these results indicate that the instrument performance as tested is very accurate and reproducible.
Conclusion
As of this writing, the Pinnacle PCX has been in place for about 15 months at our laboratory, and we have analyzed approximately 1000 carbamate environmental samples with it. The new system definitely provides an improvement in convenience: Switching columns, for example, ease of use, time saved and flexibility all appears to be enhanced. Robustness would need a longer evaluation term but, so far, performance is flawless. Pinnacle PCX post column technology is simple enough to be employed by an operator with a limited amount of experience, particularly if one uses it with proprietary standardized reagents, because the system is already optimized for the prepackaged chemistry. There’s also the matter of maintenance convenience. All that is required to ensure that problems are quickly addressed with minimal downtime is to perform the necessary reagent flushes and follow the protocol strictly. From the perspective of sensitivity, the new instrument is capable of carbamate detection limits equal to or better than its predecessor. As constructed, the Pinnacle PCX enables carrying out the necessary workflow in a very economical and productive manner for the carbamate and other analyses required by the Safe (Drinking) Water Act—EPA protocol, which we perform.
*These values were obtained using injection volumes of 30 μL, which is impressive because common injection volumes for carbamate in drinking water analysis is typically 400 μL. Using smaller injection volumes has the added benefit of extending column life and improving resolution, especially in the beginning of the chromatogram.
References
2. Munch, J.W., ed. 1995. METHOD 531.1: Measurement of N-methylcarbamoyloximes and N-methylcarbamates in water by direct aqueous injection HPLC with post column derivatization, Revision 3.1. http://www.ultrasci.com/docs/analyticalmethod/method14.pdf
For more information, contact Dr. James Balk at jim.balk@hhss.ne.gov or by phone at 402-471-8462.
AT A GLANCE
• An optimized carbamate analytical system allows one to detect a spectrum of carbamates at ppb (ug/L) levels in drinking water
• The system uses a syringe pump, which delivers true pulse-free flow so there is no need for pulse-dampening components
• The columns are optimized for the specific analytical application, which saves time as there is no need to adjust the gradient program
• The system enables carrying out the necessary workflow for the carbamate and other analyses required by the Safe (Drinking) Water Act—EPA protocol
ONLINE
For additional information on the technologies discussed in this article, see Laboratory Equipment magazine online at www.LaboratoryEquipment.com or the following Web site:
• www.pickeringlabs.com
Laboratory Equipment
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