Edward Kaiser

A new approach to dealing with high-to-low concentration ratios of sodium and ammonium ions in ion chromatography

Abstract In ion chromatography, samples of very dissimilar concentration ratios of ammonium-to-sodium are difficult to quantify since these two cations have similar selectivities for stationary phases containing commonly used sulfonic acid or carboxylic acid cation-exchange functional groups. A new column with carboxylic acid and phosphonate functional groups as well as a crown ether group has been developed to address this limitation. Selectivity of the common inorganic cations is different from conventional columns in that the separation between sodium and ammonium has been greatly increased, and potassium ion elutes after magnesium and calcium. Applications involving very dissimilar concentration ratios of cations can now be done isocratically, with a single column. Other applications of this new column will also be discussed.

Determination of trace anions in concentrated weak acids by ion chromatography.

Ion-exclusion chromatography (ICE) followed by ion chromatography (IC) was used for the determination of trace anionic contaminants in concentrated weak acids. The ICE separation was used as a pretreatment step to isolate the contaminant anions of strong acid from the excess of matrix ions. Then a fraction containing the analyte ions was separated using IC with suppressed conductivity detection. Microbore-ion-exchange columns were chosen to address the increased purity requirements for use of these concentrated acids in semiconductor applications. The chromatographic conditions were optimized for determining trace chloride, sulfate, phosphate, and nitrate in concentrated 24.5% (v/v) hydrofluoric acid; trace chloride, sulfate, and nitrate in concentrated 85% (w/w) phosphoric acid and trace chloride and sulfate in concentrated 0.7% (v/v) glycolic acid. Method detection limits for the anions of interest were below 100 micrograms/l.

Determination of trace level ions by high-volume direct-injection ion chromatography

Abstract A high-volume direct-injection method was developed for the purpose of trace level determinations (low to sub-μg/l) of anions and cations by ion chromatography. The chromatographic signal was enhanced by increasing the sample volume up to 1300 μl with no significant loss in peak efficiency. The following parameters were optimized for minimizing noise: eluent flow, background conductance, suppressor chemistry, conductivity temperature and data filtering. Total analysis times were less than 30 min and the method detection limits for most ions ranged from 10 to 400 ng/l (ppt).

Determination of trace anions in high-nitrate matrices by ion chromatography.

An ion chromatography method was developed to determine trace anionic contamination in matrices that have a high concentration of nitrate ion. Contaminant anions of interest were separated on an IonPac AS15 high-capacity anion-exchange column and detected by suppressed conductivity detection. An EG40 eluent generator was used to prepare high-purity and carbonate-free potassium hydroxide. Using the EG40, performance at trace levels was enhanced because background conductivity decreased and retention time reproducibility improved. Trace anionic contamination from the mobile phase was minimized when using the eluent generator compared to using conventionally prepared sodium hydroxide eluents. The signal-to-noise ratio was also improved with the use of a temperature controlled conductivity cell and chromatography hardware in the microbore (2-mm) format. The eluent concentration was optimized to separate the contaminant anions from the excess of the nitrate matrix ions. The procedure was demonstrated for a solution of reagent-grade sodium nitrate and high-purity 0.7% nitric acid. Method detection limits for chloride, sulfate and phosphate of 150 microg/l and lower were achieved.

Determination of trace anions in organic solvents.

Ion chromatography along with matrix elimination was used to reliably determine trace levels of anionic contaminants in organic solvents. A 5-ml sample volume was injected directly into the instrument without any sample pretreatment. High-purity deionized water was used to deliver the sample to a preconcentration column, where the anions of interest were retained while the organic matrix was rinsed to waste. A sodium carbonate eluent eluted concentrated anions from the preconcentration column and separated them on a 2-mm pellicular anion-exchange column. The separated anions were detected by suppressed conductivity. This method was used to determine the anionic contaminants of isopropanol, acetone and N-methylpyrrolidone. Method detection limits for chloride, nitrate, sulfate and phosphate were all lower than 1 microg/l.

Determination of trace anions in isopropanol

Abstract Ion chromatography along with matrix elimination reliably determines low μg/1 levels of anionic contaminants in isopropanol. The use of ion-exchange columns that are solvent compatible makes elimination of the isopropanol sample matrix possible and allows calibration standards to be prepared in deionized water. By concentrating a large amount of sample, detection limits for chloride, sulfate, phosphate and nitrate between 0.2 and 1.0 μg/1 are achieved. The sample can be injected without sample pretreatment. The procedure is automated and yields a complete analysis in less than 1 h.

Development and validation of an assay for iodide in serum using ion chromatography with pulsed amperometric detection

We developed and validated an ion chromatography method to assay iodide in serum sampled from rats and rabbits that had been exposed to iodomethane. Iodomethane is of interest because it is a volatile liquid pre-plant soil crop protection fumigant that has been proposed as a non-ozone-depleting alternative to methyl bromide. Serum was prepared from whole blood collected on wet ice at the time of sacrifice and kept frozen at less than −65°C. For analysis, serum samples were thawed unassisted at ambient temperature. Proteins were separated from the serum samples by ultrafiltration. A 100-μl filtered serum sample was then injected into the ion chromatograph without additional sample preparation. Iodide was separated in <20 min by anion-exchange chromatography using a 25-mM nitric acid eluent. The analyte of interest was detected by pulsed amperometry using a silver working electrode. The method showed linear response over the concentration range of 100 to 5000 ng/ml iodide (r2 > .998) with a lower limit of quantitation of 100 ng/ml iodide. The accuracy of the procedure, determined by spiked recovery measurements at 100 ng/ml iodide, was between 90 and 110%. A method detection limit of 20 ng/ml for iodide in serum samples was demonstrated using the method of standard additions.

Monitoring trace anion contamination in disk drive components

Ion chromatography was used to determine trace anionic contamination on the surface of hard disk drive components. These contaminants can have a detrimental effect on device reliability and yield. Disk drive components were soaked in deionized water and these extracts were analyzed for anions. The anions fluoride, acetate, formate, acrylate, methacrylate, chloride, nitrite, bromide, nitrate, benzoate, sulfate, oxalate, phthalate and phosphate were separated on a high-performance anion-exchange column and determined at concentrations less than 1 microg/l with suppressed conductivity detection. The extract solutions were analyzed either by injecting 1 ml or by preconcentrating 5 ml. We evaluated the performance of both methods.

Analysis And Control Of Copper Plating Bath Additives And By-Products

New copper plating bath chemisties are being developed to meet the emerging need of plating copper into submicron features on semiconductor wafers. These chemistries are designed to provide a fast, efficient, fill for even the most challenging wafer terrain. It has been found that maintaining the concentration of the additives in these plating baths at certain levels is critical to the performance of the bath. Plating technology for semiconductor applications requires rigid bath control and disciplined methodology. Establishing correlations between what is found in the plated film and bath chemistry control parameters is fundamental in producing interconnects that are consistent and reliable. To establish these correlations, it is important to have a clear understanding of the chemical composition of the bath. It is theorized that the “suppressor” bath components help moderate the deposition rate of the copper fill and the “leveler” additives improve the topology of the copper overfill. Too much or too li...