Table 2: Parameter comparison of the digital refractometers used for this study.
Instrument |
Rudolph Research J357CC |
Reichert TS D (1st generation)a) |
Type |
Analytical refractometer |
Clinical refractometer |
Applications |
RI, Brix, custom scale |
RI, Brix, %serum protein, urine SG, % CuSO4 |
Serum protein (% = g/100 mL) |
Not implemented |
0.0-15.0 (dn/dc not stated) |
Installation/operation |
Bench-top |
Bench-top and handheld |
Light source |
589.3 nm LED |
589.3 nm LED |
Prism |
Sapphire (nD = 1.7681) |
Heavy crown glass (nD = 1.60994)a) |
Sample well |
Stainless steel |
Stainless steel |
Detector |
CCD pixel array b) |
CCD pixel array, 3648 pixels a) |
RI range |
1.26 - 1.70 |
1.33-1.56 |
RI resolution |
0.00001 nD |
0.0001 nD |
Temperature resolution |
0.01 °C |
0.1 °C |
Temperature accuracy |
± 0.01 °C (thermostatization) |
± 0.2 °C (measurement) |
Temperature compensation |
4 - 95 °C (sucrose Brix) |
15-40 °C (sucrose Brix) |
Precision |
0.00002 nD |
0.0001 nD |
Accuracy (for protein) |
± 0.00002 nD (~ 0.1 mg/mL) |
± 0.0001 nD (~ 0.5 mg/mL) |
Zero calibration |
Water, air |
Water |
Dimensions (L × W × H, cm) |
43.5 × 30.5 × 33 (lid open) |
18 × 9 × 3.5 (no lid) |
Weight (kg) |
10.4 |
0.41 |
User interface |
Touchscreen, USB keyboard |
Three keys, double-line alphanumeric display |
Communication ports |
USB, RS-232, ethernet |
IR to optional IR receiver connected to PC |
21 CFR 11 compliance |
Optional |
Not stated |
Power |
AC mains |
6 V DC (4 × AAA batteries) |
Cost (approximate USD) |
~ 15,000 |
1,385 (MSRP, current version) |
Remarks: a) 1st instrument generation according to patent description; the current version is equipped with a sapphire prism; b) The overall number of sensor pixels is less relevant than the accuracy of the shadow-line location algorithm.