United States environmental protection agency perchlorate method 332.0. Statistically sound recovery studies in simulated drinking water.

This research is a continuation of an earlier work, which evaluated the United States Environmental Protection Agency's Perchlorate Method 332.0, in which standards were prepared in deionized water over an extended concentration range (i.e., to a maximum of 200 µg/L). This current paper investigates the performance of the same method in which standards were made in simulated drinking water. A microbore format with a 15-µL injection volume was employed to conduct a recovery study and generate recovery curves (which hold the key to a statistically sound assessment of method performance in more complex matrices). The maximum analyte concentration range was 1 to 200 µg/L. For various subset concentration ranges, recovery evaluations were made using both raw peak-area data and analyte responses scaled by the internal standard (ISTD). The results indicate that in complicated matrices such as drinking water, ISTDs may not provide simultaneously high precision and recovery.

United States Environmental Protection Agency perchlorate method 332.0 via microbore and capillary chromatographic formats: statistical evaluation of the use of (18)O-perchlorate internal standard with deionized-water matrices.

A statistically sound evaluation is made of the United States Environmental Protection Agency's perchlorate Method 332.0 by tandem ion chromatography-mass spectrometry-mass spectrometry. Two microbore formats and one capillary format are used with a deionized-water matrix. The evaluation is made for raw peak-area data and for analyte responses scaled by the internal standard, over an analyte concentration range of 0.25 to 200 microg/L. Results indicate that: (i) the internal-standard signal is suppressed by the analyte in both microbore formats; (ii) the analyte signal is not affected by the internal standard; (iii) models for the calibration curves usually contain bias; (iv) the measurement uncertainty is similar in magnitude for both the peak-area- and ratio-based curves.

Approaches to sample pretreatment in the determination of perchlorate in real world samples.

Perchlorate can be determined by the tandem technique of ion chromatography (IC) coupled to electrospray ionization mass spectrometry (ESI-MS). However, detection by ESI-MS can be compromised by the coelution of matrix components that can suppress the analyte signal. In addition, the presence of surface-active and other types of matrix components can cause fouling of the electrospray inlet, reducing overall signal and requiring frequent maintenance. The influences of matrix components can be minimized by using analytical columns with different selectivities, in-line diversion of separated matrix components, and off-line selective removal of matrix components via ion exchange or adsorption. This paper will discuss these sample preparation approaches for samples containing anionic species including surfactants and inorganic ions that elute in the vicinity of perchlorate.

Applications of ion chromatography with electrospray mass spectrometric detection to the determination of environmental contaminants in water.

Ion chromatography (IC) is widely used for the compliance monitoring of common inorganic anions in drinking water. However, there has recently been considerable interest in the development of IC methods to meet regulatory requirements for analytes other than common inorganic anions, including disinfection byproduct anions, perchlorate, and haloacetic acids. Many of these new methods require the use of large injection volumes, high capacity columns and analyte specific detection schemes, such as inductively coupled plasma mass spectrometry or postcolumn reaction with UV-Vis detection, in order to meet current regulatory objectives. Electrospray ionization mass spectrometry (ESI-MS) is a detection technique that is particularly suitable for the analysis of permanently ionized or polar, ionizable compounds. The combination of IC with MS detection is emerging as an important tool for the analysis of ionic compounds in drinking water, as it provides increased specificity and sensitivity compared to conductivity detection. This paper reports on the application of IC-ESI-MS for the confirmation and quantitation of environmentally significant contaminants, i.e. compounds with adverse health effects which are either regulated or being considered for regulation, such as bromate, perchlorate, haloacetic acids, and selenium species, in various water samples.

Removal of metallic impurities from mobile phases in reversed-phase high-performance liquid chromatography by the use of an in-line chelation column.

An in-line stripper column packed with iminodiacetate chelation resin is placed between the pump and injection valve and shown to remove metallic impurities from an HPLC system. We used a test procedure based on assessing the relative peak asymmetries of 2,2'-bipyridyl, a chelating analyte and 4,4'-bipyridyl, a non-chelating analyte. Results from use of polyether ether ketone (PEEK) and stainless steel pumps are evaluated. Analytical columns with titanium/PEEK and stainless steel frits are used to assess the role of frits in metallic contamination. We demonstrated that although metal-free pumping systems contribute significantly lower metallic impurities than stainless steel systems, metal is nevertheless present in the mobile phase and the chelating stripper columns were found useful in protecting the analytical columns from contamination. The stainless steel frits were not found to be significant contributors to the contamination.

Low-level calibration study for a new ion chromatographic column to determine borate in deionized water.

In the semiconductor industry, there is interest in determining borate at sub-ppb levels in ultrapure water, since borate is an early breakthrough ion from ion-exchange resin beds. Although dissolved silica is the most common species currently used to monitor the breakdown of the deionization systems, it is thought that borate probably breaks through earlier than silicate. To be of use as an early-warning indicator, borate must be determined at ppt levels. This paper discusses benchtop results with several new column products designed to deliver low-ppt detection limits for boron as borate. The system uses a prototype borate-specific concentrator column that is coupled to an ion-exclusion separator and suppressed-conductivity detection. The acidic eluent, containing mannitol, quantitatively elutes the borate from the concentrator. The analytical separation is performed using a specially designed ion-exclusion column. Data presented are from two multilevel calibration studies. Included is a discussion of detection-limit calculations and recommended formats for reporting results.

Protein variant separations by cation-exchange chromatography on tentacle-type polymeric stationary phases.

We developed a set of prototype cation-exchange column packings that are based on a hydrophilic coated, pellicular polymeric support with a grafted tentacular surface chemistry that is highly suited to resolving closely related protein variants. These column packings (1) afford minimal band spreading in conjunction with extremely high selectivity, (2) exhibit a very hydrophilic character and (3) have moderate loading capacity. Cytochrome c variants (bovine, horse, rabbit) were baseline-separated, as was native ribonuclease A and its two deamidation products, the Asp67 and isoAsp67 forms. Humanized monoclonal antibody variants differing in the presence of lysine at the C terminus of the heavy chains were baseline-resolved. Finally, the separation of hemoglobin variants found in a sample containing elevated levels of glycated hemoglobin was also demonstrated.

Eliminating amino acid and peptide interference in high-performance anion-exchange pulsed amperometric detection glycoprotein monosaccharide analysis.

The monosaccharide content of a glycoprotein is often determined by acid hydrolysis at elevated temperature and subsequent high pH chromatography of the released, underivatized monosaccharides on pellicular anion-exchange resin (HPAE) using pulsed amperometric detection (PAD). We have found that for glycoproteins with low levels of glycosylation, monosaccharide quantitation can be compromised by amino acids fouling the working electrode surface. Specifically, lysine elutes on the CarboPac PA1 column just prior to galactosamine, whereas remaining amino acids and most peptides elute after the monosaccharides and do not interfere with monosaccharide quantification. A direct comparison of PAD vs Abs215 detection of lysine using the CarboPac PA1 column as the separator reveals that lysine does not cleanly come off the working electrode. The monosaccharide response inhibition caused by lysine could be corrected by the posthydrolysis addition of a rhamnose internal standard and the determination of "correction factors." We have developed a guard column with an altered selectivity for amino acids which, when used with a new separator, causes lysine to elute after the monosaccharides and also causes hydrophobic amino acids to elute further after the monosaccharides. Together the new separator and guard columns solve the lysine fouling problem, reduce sample-related baseline noise, and reduce the magnitude of correction factors.