An integrated electrophoretic mobility control device with split design for signal improvement in liquid chromatography-electrospray ionization mass spectrometry analysis of aminoglycosides using a heptafluorobutyric acid containing mobile phase.

Electrophoretic mobility control (EMC) was used to alleviate the adverse effect of the ion-pairing agent heptafluorobutyric acid (HFBA) in the liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) analysis of aminoglycosides. Aminoglycosides separated by LC were directed to a connecting column before their detection via ESI. Applying an electric field across the connecting column caused the positively charged aminoglycosides to migrate toward the mass spectrometer whereas the HFBA anions remained in the junction reservoir, thus alleviating the ion suppression caused by HFBA. To accommodate the flow rate of a narrow-bore column, minimize the effect of electrophoretic mobility on separation, and facilitate the operation, an integrated EMC device with a split design was fabricated. With the proposed EMC device, the signals of aminoglycosides were enhanced by a factor of 5-85 without affecting the separation efficiency or elution order. For the analysis of aminoglycosides in bovine milk, the proposed approach demonstrates a sensitivity that is at least 10 times below the maximum residue limits set by most countries.

A convenient and sensitive method for haloacetic acid analysis in tap water by on-line field-amplified sample-stacking CE-ESI-MS.

In this study, we propose a simple strategy based on flow injection and field-amplified sample-stacking CE-ESI-MS/MS to analyze haloacetic acids (HAAs) in tap water. Tap water was passed through a desalination cartridge before field-amplified sample-stacking CE-ESI-MS/MS analysis to reduce sample salinity. With this treatment, the signals of the HAAs increased 300- to 1400-fold. The LODs for tap water analysis were in the range of 10 to 100 ng/L, except for the LOD of monochloroacetic acid (1 µg/L in selected-ion monitoring mode detection). The proposed method is fast, convenient, and sensitive enough to perform on-line analysis of five HAAs in the tap water of Taipei City. Four HAAs, including trichloroacetic acid, dichloroacetic acid, dibromoacetic acid, and monobromoacetic acid, were detected at concentrations of approximately 1.74, 1.15, 0.16, and 0.15 ppb, respectively.

Estimation of the measurement uncertainty in quantitative determination of ketamine and norketamine in urine using a one-point calibration method.

An approach was proposed for the estimation of measurement uncertainty for analytical methods based on one-point calibration. The proposed approach is similar to the popular multiple-point calibration approach. However, the standard deviation of calibration was estimated externally. The approach was applied to the estimation of measurement uncertainty for the quantitative determination of ketamine (K) and norketamine (NK) at a 100 ng/mL threshold concentration in urine. In addition to uncertainty due to calibration, sample analysis was the other major source of uncertainty. To include the variation due to matrix effect and temporal effect in sample analysis, different blank urines were spiked with K and NK and analyzed at equal time intervals within and between batches. The expanded uncertainties (k = 2) were estimated to be 10 and 8 ng/mL for K and NK, respectively.

Chiral electrokinetic chromatography-electrospray ionization-mass spectrometry using a double junction interface.

A double junction interface was utilized to preserve separation efficiency and alleviate ion suppression from sulfated ß-cyclodextrin (S-ß-CD) in electrokinetic chromatography-electrospray ionization-mass spectrometry. The utility of the approach was demonstrated by chiral EKC-MS analysis of dihydroxyphenylalanine and methyldihydroxyphenylalanine enantiomers using either low concentration (counter-migration mode; 0.1% S-ß-CD) or high concentration (carrier mode; 2% S-ß-CD). In the counter-migration mode, S-ß-CD anions were supplied continuously from the junction reservoir to the separation column so that the effective separation length was preserved. This interface is especially useful under carrier mode in which high concentration of S-ß-CD will migrate toward the ESI source. With the use of the double junction interface, the S-ß-CD exited the separation column will remain in the junction reservoir, whereas the analyte will flow toward the ESI source through a connecting column. As a result, no ion suppression was observed and the sensitivity was improved significantly.