No abstract

We present procedures for determining theophylline in 50 mul of serum. The drug is extracted into a small volume of solvent that contains an internal standard, 8-chlorotheophylline. The extract is Analyzed by isocratic reversedphase chromatography, with measurement of eluted theophylline at 273 nm. Day-to-day reproducibility within 5% is attainable for the concentration range 5--20 mg/liter. Other xanthines and related metabolites do not interfere. Sensitivity is 1 mg/liter. The correlation coefficient, when results by a spectrophotometric procedure were compared, was 0.989. Amobarbital, secobarbital, phenobarbital, and diphenylhydantoin do not interfere. Total analysis time for a single sample is 15 min.

No abstract

No abstract

A glass open tubular (capillary) column together with a nitrogen-selective detector were evaluated for the analysis of amino acids by gas chromatography. Test samples included normal and abnormal human sera and urine and several hydrolysates of pure proteins. Amino acids in the biological samples were isolated by ion exchange pretreatment and derivatized to the n-propyl, N-acetyl derivatives. Protein hydrolysates were derivatized without pretreatment. Compared with a flame ionization detector, the nitrogen-selective detector gave a sensitivity enhancement of 80x-180x for the amino acid derivatives, depending on the particular amino acid. Long-term stability of the detector was excellent. Reproducibility studies gave a long-term precision of about 6% for serum or urine samples while a precision of 5% was obtainable on a day-to-day basis when analyzing protein hydrolyzates. The experiments showed that amino acids at the picomole level could be reliably analyzed with the system. The open tubular column coated with a mixture of Carbowax 20M and Silar 5 CP and having a very thin liquid phase film gave greatly improved thermal stability compared with a previously used packed column.