Abstract: A flow system with built-in capability to adjust injection volume whenever sample concentration. is higher than the upper linearity limit was developed and its performance assessed. Solenoid valves were used to manage sample and carrier delivery. Whenever the peak height is higher than the calculated linearity limit an injection volume adjustment is made to a 2nd determination of the same sample in such a way that the peak height will be in the linear range. Extended linear range is therefore achieved without sacrificing detection of low concentration. samples. Calibration, calculation of the upper linearity limit and model fitting to calibration data (peak height vs. concentration. and peak height vs. injection volume) are automatically performed with no human intervention. Performance was tested upon assessing dissolution profiles of cephalexin tablets in a low dispersion manifold with direct UV determination The proposed system presents a 180 determinations h-1 throughput. Sample aspiration time was calibrated in the range 50-2000 ms, thus allowing quantification up to 1250 mg L-1 of cephalexin. Precision is ~0.95% relative standard deviation when sample is aspirated for 2000 ms. Results obtained are comparable to those obtained by using the reference procedure.

Abstract: Antibiotic β-lactams with a C6 side-chain [e.g., penicillin X(I) and benzylpenicillin(II)] were pre-derivatized with imidazole and a salt of Ni(II), Zn(II), Ag+, Cd(II), Au+ or Hg(II) (HgCl2 best) before analysis by HPLC on a column (20 cm x 4.6 mm) of Spherisorb C18 (5 µm) with aqueous 0.01 M NaH2PO4 buffer (pH 6.5) - acetonitrile (4:1), 0.01 M in complexing agent (EDTA, NaCN or Na2S2O3), as mobile phase (1.5 mL min-1) and detection at 325 nm. Although NaCN was the best complexing agent, the less toxic ones were preferred. With use of EDTA and HgCl2 calibration graphs based on peak area were rectilinear for up to 50 µg mL-1 of I and II; for determination of 25 µg mL-1 of I, the coefficient of variation was 2% (n = 10). With Na2S2O3, the detection limits were 0.5 µg mL-1 for I and II. β-Lactams with a primary amino-group, e.g., 6-aminopenicillanic acid(III) and cephamycin C(IV), were separated on a column (20 cm x 4.6 mm) of Spherisorb C8 with acetonitrile - 0.01 M phosphate buffer of pH 5.5 containing 0.01 M butylammonium hydroxide and 0.2% of acetic acid (1:19) as mobile phase (1.5 mL min-1), post-column derivatization with phthalaldehyde and 2-mercaptoethanol and fluorimetric detection at 450 nm (excitation at 350 nm). Hydrolysis on a column of Amberlite IRA-120 before derivatization improved sensitivity for, e.g., III. Calibration graphs for (IV) and adicillin (V) were rectilinear in the range 0 to 100 µg mL-1. In analysis of a sample containing 100 µg mL-1 of (IV) the coefficient of variation was 2% (n = 20). The detection limits for (IV) and V were 0.5 to 1.0 µg mL-1 and for ampicillin, cephalexin and cephradine were 26, 14 and 8 µg mL-1, respectively.

Abstract: Plasma or urine (10 µL) was applied to a column (25 cm x 4 mm) of LiChrosorb RP-18 (7 µm), fitted with a guard column (1 cm x 4 mm) of the same material, with 25 mM phosphate buffer of pH 7.0 - acetonitrile (19:1, 9:1 or 17:3) as mobile phase (1 mL min-1). Post-column derivatization was performed in a PTFE coil (4.5 m x 0.25 mm) with fluorescamine solution (0.2 mg mL-1) in acetonitrile at 0.25 mL min-1. Fluorimetric detection was at 485 nm (excitation at 385 nm). Calibration graphs were rectilinear from 10 to 500 ng of cefaclor, cephalexin, cephradine, cefroxadine, cephaloglycin and cefadroxil. Detection limits ranged from 0.3 to 1.8 ng, and coefficient of variation (n = 12) were 4%. Recoveries were generally 90%.