Enzymatic determination of sodium and chloride in sweat.
OBJECTIVE
To develop methods based on enzyme activation for the analysis of sweat sodium and chloride using beta-galactosidase and alpha-amylase, respectively.


METHODS
Both were monitored kinetically on the Cobas Fara centrifugal analyzer. The sweat, collected with the Macroduct system, was diluted no more than five-fold for the volumes obtained of 16 to 80 mu L, median 32.5 mu L. The sodium assay utilized a sodium-binding cryptand to maximize linearity.


RESULTS
Between-run coefficients of variation (%) at 10, 20, and 50 mmol/L were 3.6, 4.5, and 1.3 for sodium and 7.1, 6.1, and 6.0 for chloride, respectively. The sodium method showed excellent agreement with flame photometry (y = 0.997x + 0.742; r = 0.998), and chloride with a mercuric thiocyanate method (y = 0.995x + 0.485; r = 0.996), giving equivalent discrimination between patients with and without cystic fibrosis.


CONCLUSIONS
The methods enable the rapid analysis on the same analyzer of both sodium and chloride in a single dilution of sweat collections of low volume.
Taylor
R P
RP
Department of Clinical Biochemistry, John Radcliffe Hospital, Headington, Oxford, UK.
James
T J
TJ
D019086:Bridged Bicyclo Compounds, Heterocyclic; D002614:Chelating Agents; D002712:Chlorides / Q000032:analysis*; D003550:Cystic Fibrosis / Q000175:diagnosis; D004789:Enzyme Activation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D016014:Linear Models; D009598:Nitrophenylgalactosides / Q000378:metabolism; D010783:Photometry / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012964:Sodium / Q000032:analysis*; D013542:Sweat / Q000737:chemistry*; D000516:alpha-Amylases / Q000378:metabolism; D001616:beta-Galactosidase / Q000378:metabolism
D019086:Bridged Bicyclo Compounds, Heterocyclic; D002614:Chelating Agents; D002712:Chlorides; C055012:2-nitrophenylgalactoside; D009598:Nitrophenylgalactosides; C053547:cryptating agent 221; D012964:Sodium; D000516:alpha-Amylases; D001616:beta-Galactosidase