Automatic Syringe for the Milko-Tester

TECHNICAL NOTES

raining 5% of fat. Optical density measurements were made at the absorption maximum for the copper-arazate complex. The results presented in Fig. 3 show that carotene concentrations representative of the lower ranges normally found in milk (3) would absorb light significantly at this wavelength. These results indicate that the rapid method of Smith (8) for copper determination in whole milk nmst be used and interpreted carefully. While other components in the milk system may contribute to error and variability in the colorimetric determination of copper by the rapid method, our results show that the interference of carotene may be particularly significant in whole milk. Comparison of results between milk samples of different carotene concentrations probably are not valid, unless an adjustment of the results is made for the carotene. B. C. ARMSTRONG and C. W. DILL Department of Animal Science Texas A&M University College Station

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References

(1) Drabkin, D. L. 1939. Report on copper. J. Ass. Oflic. Agr. Chemists, 22:320. (2) Hetrick, J. H., and P. H. Tracy. 1945. The determination of copper in milk powder by a direct carbamate method. J. Milk Technoh, 8:5. (3) Jenness, R., and S. Patton. 1959. Principles of Dairy Chemistry. John Wiley and Sons, New York. (4) King, R. L., and W. L. Dunkley. 1959. Relation of natural copper in milk to incidence of spontaneous oxidized flavor. J. Dairy Sci., 42: 420. (5) McDowel], A. K. R. 1947. The estimation of copper and iron in cream and dry butterfat. J. Dairy Res., 15: 70. (6) Miller, D. E., and P. H. Tracy. 1952. The copper content of butter made by a. continuous method. J. Dairy Sci., 35: 292. (7) Scott, A. I. 1964. Interpretation of the Ultra-Violet Spectra of Natural Products. Pergamon Press, Oxford. (8) Smith, A. C. 1967. Rapid methods for determining copper content of milk. J. Dairy Sci., 50 : 664.

Automatic Syringe for the Milko-Tester Abstract

The installation on the Milko-Tester of an automatic pipetting machine to dispense the ¥ersene diluent is described. I t is activated when the sample funnel is moved to the collection position. The modification reduces the hand motions required to test a sample of milk from three to two and does not change the accuracy of the MilkoTester. Procedures

The normal procedure for operating the Milko-Tester1 is to start the homogenizer to flush the previous sample from the instrument. When the homogenizer stops, a measured volume of homogenized milk is in the milk pipette (Fig. 1). The operator moves a funnel into position and simultaneously collects and dilutes the milk sample by forcing a Versene solution through the pipette with a fixed-volume syringe. The syringe and funnel are returned to their normal positions with springs. The diluted milk 1DeLaval Separator Co., Poughkeepsie, N.Y. 2Will Scientific Corporation, Rochester, N.Y. 3Potter & Brumfield KRP5AG, Allied Radio, Chicago, Ill. 4Amperite 115NO2, Allied Radio, Chicago, Ill. 5Potter & Brumfield KB17AY, Allied Radio, Chicago, Ill.

then flows into the photometer. The collectiondilution step requires both of the operator's hands and resistance of the syringe can be high. This note describes the installation of an automatic syringe activated by motion of the collection funnel. A Brewer Model 40 Automatic Pipetting Machine2 equipped with a 20-ml syringe is connected to the Milko-Tester mixing valve as shown in Fig. 1. A control system operates the pipetter for one cycle when the collection funnel is moved into position by the operator. After all of the diluent is in the funnel, the funnel is returned to the rest position and the diluted milk flows into the photometer as before. The controls then reset for the next sample. A schematic diagram of the entire modification is shown in Fig. 2. A notch filed in the cam of the pipetter opens Microswiteh $2 so that the pipetter motor stops at the start of the syringefilling portion of the cycle. Moving the funnel to the collection position closes Microswitch $3, located at the rear of the funnel guides. This energizes the coils of both Relay R Y F to start the pipetter motor and Relay RY2 ~ to change latching Relay RY3 ~ to the open position. As soon as the motor starts, $2 is closed by the cam, so RY1 remains closed and the motor runs until $2 is opened by the cam. The thermal delay Relay RY2 opens 2 see after it is closed. When the pipetter motor stops after delivering the diluent, the operator returns the sample J. DAIRY SCIENCE, VOL. 51, NO. 11

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OF DAIRY

funnel to the normal, or rest position, where the diluted milk sample enters the photometer systenl. When the funnel reaches the rest position, Microswitch $4 is closed, causing RY3 to reset. Unless the relay is reset, closure of $3 will not start the pipetter, thereby eliminating inadvertent double dilution of the milk. I n the case of high-testing milk where double dilution is desired, a separate switch, $4, is used to reset RY3 and the second cycle starts immediately, since $3 is still closed. Calibration of the modified Milko-Tester is analogous to the calibration of the original machine. The amount of diluent is adjusted according to instructions with the pipetter until the differences between the machine and Babcock readings on a series of test milks are with-

plM/LTK |

I

SCIENCE

in the tolerances established for the MilkoTester. After calibration, the pipetter delivers 5.74 g diluent with a standard deviation of ±0.06 g (30 trials). The coefficient of variation is 1%, which compares favorably to hand-operated Cornwall syringes. With the operator's right hand free to prepare samples and record data, full utilization of the inherent speed of the Milko-Tester can be approached more closely. We have tested 360 sampies in two hours with just one opera~or, using the modified instrument. The system has been used on over 128,000 samples with no failures.

J. W. SHERBON

Departmentof FoodScience CornellUniversity,Ithaca,NewYork

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FIG. 1. Plan view of Milko-Tester with automatic syringe instaIled.

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