Applications of Ion Chromatography in the Public Health Sector and Advances in Chromatography Systems at IICS 2011

Never before have I attended a meeting that concisely addressed so many topics of current public concern. Some examples include: disinfecting fruit to protect against E. coli, Listeria, and Salmonella; drinking water analysis to test for toxins, including bromate and perchlorate at 20 ppt or less; rapid assay for chromate in nutraceuticals and water; speciation of arsenic residues in food and beverages (including apples) and tissue to estimate toxicity; and characterization of pre- and post-blast explosive residues and linking them to probable sources. All of this was covered in an intense, three-day symposium—the 23rd International Ion Chromatography Symposium (IICS 2011), held October 16–19 at the Marriott Hotel in Providence, RI.

Additionally, lectures described novel practical advances in chromatography systems such as IC-MS, IC-ICP, instruments for multidimensional IC-IC, IC-capillary IC, matrix elimination, and automated mobile phase preparation. Several new columns were introduced or previewed, including one that appears to separate anions by the chelation effect.

Ion chromatography in the public health sector

Use of ClO2 to reduce bacterial contamination

A month before the meeting, cantaloupes contaminated with Listeria were shipped from a packing shed in Colorado. Several consumers died. Most of the crop was recalled and destroyed. Dr. Valentina Trinetta (Purdue University, Lafayette, IN) reported that chlorine dioxide (ClO2) is a strongly oxidizing gas that is being investigated as a possible bactericide for foods. ClO2 reduces bacterial contamination from the natural state by 103–104. Plus, the disinfection by-products are chlorite, chlorate, and chloride. Dr. Trinetta studied the time course of ClO2-treated vegetables. The oxychloride residues decrease rapidly to chloride in a matter of days after exposure. Simple washing further removes the residues below the level of concern.

Use of diffuse reflectance to determine toxicity profile

The toxicity profile of many elements depends on their chemical state. For example, Cr(III) is an essential nutrient, while Cr(VI) is toxic to the liver and kidneys. Assays for chromium in samples need to correctly segment the two-oxidation states to prevent possible interconversion. Prof. James Fritz of Iowa State University (Ames) developed a quick sample prep protocol based on ion exchange. Cr(VI) is present as CrO4=, while Cr(III) is a cation. Thus, he created a filter stack with an anion exchange membrane to retain the CrO4=. Cr(III) is retained on the lower cation exchange membrane. A common plastic syringe is the pump and volume measurement. The analytes are read with a handheld diffuse reflectance spectrometer (DRS). This is such a simple solution to a potentially difficult problem. Several other lecturers reported advances in high-sensitivity assay of Cr(VI) in nutraceuticals, various waters, etc.

Use of IC-MS/ICP-MS to assay chemicals and contaminants in beverages

Bromate is a disinfection by-product arising when ozone is used with bromide containing water. Dr. Elizabeth Hobbs of PepsiCo, Inc. (Cork County, U.K.) described IC and IC-MS systems for assaying bromate and perchlorate in beverages with low ppt method detection limits. Her lab supports bottling operations globally. The IC systems are routinely run 24 × 7 since continuous operation provides the most stable and sensitive performance.

Just before the Listeria issue hit the headlines, arsenic contamination of apple juice was a scare. Again, the risk depends on the particular species. Plus, sample handling is a major concern since As(III) is readily oxidized to As(V). Prof. Diane Beauchemin (Queens College, Kingston, Canada) used IC-ICP-MS to quickly assay arsenic species in various metabolic pathways.

IC vs HPLC and ultra-HPLC

Ion chromatography has several technical constraints that set it apart from mainline HPLC and especially ultrahigh-performance liquid chromatography (UHPLC). The flow path needs to be nonmetallic to prevent corrosion. PEEK is commonly used, but this limits the Pmax to 5000 psi. Eluent generation and regeneration components have similar Pmax limits.

Fortunately, working within this constraint is not difficult. Prof. Greg Dicinoski (University of Tasmania, Australia) and Jeff Rohrer (Thermo Fisher Scientific, Sunnyvale, CA) presented a workshop on multidimensional separations. They segmented the topic into comprehensive and focused separations. Comprehensive separations add resolution to most of the components of the sample, while heartcutting and matrix elimination focus in on specific analytes such as explosive residues. Extraneous material goes to waste. Instrument automation is essential since validating assays requires precisely repeating events, run to run.

For example, the brute force approach of sub-2-μm packed beds (i.e., UHPLC) is replaced by 2-D separations often involving heartcutting. This is particularly effective for detecting trace amounts of oxyhalides in samples with a high salt background, which is called matrix elimination. Since two columns are involved, the internal diameter of the second column can be reduced by 2–10 times, which improves detection sensitivity by four to 100×.

According to Dr. Herb Wagner, the U.S. EPA is eager to see these methods adopted. He reported on the development of a basic document that includes the definitions of many terms that are unique to 2-D.

2-D separation technology

Scientists often want see all the components of the sample. Conventionally this requires long columns with even longer run times. Since these are impractical, especially in IC, 2-D technology is now being investigated. Two-dimensional technology uses a long analytical column in the first dimension and a short, fatter column in the second. The computerized output is a two-dimensional heat map with the primary separation along the x-axis. Responses from the short column are presented along the y-axis for each slice. Peak intensity is presented by color. This technology improves the peak count by 4–10 times, with no increase in total run time. Explosive residues are an example where a variety of analytes can be expected.

Ion chromatography instruments

Measuring liquid volumes is a core competency of Metrohm AG (Herisau, Switzerland). One example is the Dosino, a mechanical burette that dispenses the volume (2–50 mL) in 10,000 increments. This can be used to form complex gradient elution where each mobile phase component is delivered by a dedicated Dosino to the inlet of the pump.

Traditionally, ion chromatography has included separation of carbohydrates by high pH anion exchange chromatography with amperometric detection. The reason, of course, is historical since Dionex (Sunnyvale, CA/acquired by Thermo Fisher Scientific) had unique technology and promoted it. This year, Metrohm introduced the 850 IC amperometric detector module for the intelligent IC instrument. The detector measures the current associated from four modes: dc (direct current), PAD (pulsed amperometric detection), flexIPAD, and CV (cyclic voltammetry) using wall-jet or thin layer cell geometry.