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.