A Simple Rapid Gaschromatographic Method for the Determination of Theophylline in Dried Whole Blood on Filter Paper Cards

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Abstract
A rapid, simple gas chromatographic method for the determination of theophylline which requires only about 35 mg dried whole blood on filter paper cards obtained by capillary blood sampling technique is described. The precision of the method studied by simultaneous analysis of 10 different samples with identical concentration revealed a coefficient of variation of 5.2%. There was a steep increase in variation of the results, when the spots preprinted on the cards were not completely stained with blood. Thus, attention has to be paid to a careful blood sampling as the most important factor for a precise and reliable determination. The method is linear over the whole range with a correlation coefficient of r = 0.9784. The analysis of 10 samples with identical concentration at 10 successive days revealed a day-to-day variance of .+-. 2.9% and no significant influence of storing the blood-stained cards at room temperature up to 10 days. Since blood viscosity and therefore the amount of blood required to stain the whole preprinted spot on the card essentially depends upon the hematocrit the influence of hematocrit values between 10-90% was studied. There was a marked effect on the determination at hematocrit values < 30% and > 60%. In the normal range between 30-60% the variation caused by different hematocrit values did not exceed 10% so that for clinical purposes a corrective calculation can be neglected.

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