known concentrates of arabinose in distilled or 

 saline water, the resulting color density varied 

 with the method used. The variation was such 



TWO-STEP METHOD 



T 



T~ 



— i 1 1 r 



20 «0 60 80 100 120 l«0 160 180 



RATE OF CARBAZ0LE REAGENT DELIVERY (SEC/27 ML) 



Figure 1. — Color density values obtained for six standard 

 water samples and for one sample taken from Galveston 

 Island's East Lagoon using two methods of carbohydrate 

 analysis at five rates of reagent addition. 



that estimates by the one-step method were higher 

 than those obtained by the two-step method. We 

 also found that the precision of estimates by either 

 method is reduced if the reagent is added at a rate 

 faster than about 27 ml. — the amount required by 

 each procedure — per 65 seconds. 



These conclusions become apparent from figure 

 1, which shows the raw data used to estimate the 

 carbohydrate concentration in a water sample by 

 both methods at various rates of reagent addition. 

 If we consider only those portions of the curves 

 from the 65-second addition rate and beyond, it 

 can be seen that response of the carbohydrate 

 in the sample to the NEC reagent corresponds to 

 that of 6 to 7 mg./l. of arabinose by the one-step 

 method, and 2.5 to 3 mg./l. by the two-step method. 

 If the entire curves are considered, the sample 

 estimates of carbohydrate concentration vary from 

 about 0.3 to 7.0 mg./l. depending on the method 

 used and also on the rate of reagent addition. The 

 erratic results recorded when the reagent deliver}' 

 rate was less than about 27 ml. per 65 seconds seem 

 to be characteristic of both methods. 



LITERATURE CITED 



Zein-Eldin, Zoula P., and Bii.lje Z. Mat. 



1958. Improved N-ethylcarbazole determination of 

 carbohydrates with emphasis on sea water samples. 

 Anal. Chem. 30(12) : 1935-1941. 



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