# Determination of Cellulose Degree of Polymerization in Historical Papers with High Lignin Content
## 3 Results and Discussion
### Reliability of the Results  
Both values, M\({}_{\rm w}\) determined by SEC with UV-VIS detector and average DP\({}_{\rm v}\) determined by viscometry, are susceptible to various systematic errors due to sample preparation, detection, and interpretation of the results; therefore, the results can only be considered as relative and not absolute values. As previously described, derivatization involves a substitution of free hydroxyl groups of cellulose with phenyl isocyanates to form cellulose tricarbanilates (CTCs) for analysis in tetrahydrofuran. Generally, it is believed that these methods do not cause degradation of cellulose; however, during dissolution or derivatization, some structural changes and loss of some fractions may occur, which in turn lead to inaccurate determination of the actual molecular mass of cellulose in the sample examined [36]. Derivatization is also not straightforward when the lignin content is high; low content does not interfere. A high lignin content may be partly responsible for the overestimated M\({}_{\rm w}\) values of cellulose tricarbanilate derivatives in conventional calibration [11]. Several authors have compared different methods for determining the molecular mass of cellulose. [PERSON] and [PERSON] [16] studied pure cellulose ([PERSON] paper No. 1) in cadaveren during accelerated degradation by viscometry and by SEC using different detectors: MALS, differential refractive index (RI) for LiCl-DMAc solutions, and low-angle light scattering (LALS) and UV for the CTC derivatives. The highest values for the DP were obtained with the SEC of LiCl-DMAc solutions, lower values were obtained with the SEC of CTC derivatives, and the lowest values were obtained with viscometry. A good correlation between viscometry in CED and SEC of CTC derivatives with MALS detection for pure cellulose as well as for softwood bleached cellulose was found by [PERSON] et al. [8]. In the study by [PERSON] et al. [36], three methods for the analysis of carbanulated cellulose derivatives dissolved in THF were compared: SEC with MALS detection, SEC in combination with diode-array detector and calibration with polystyrene standards (SEC DAD), and asymmetric flow field-flow fractionation in combination with a multiangle light scattering (A4F-MALS). Each of the methods provided different absolute values of molecular mass, but the mutual correlations between them were linear with high correlation coefficients (r = 0.990-0.992); thus, each of the methods studied can be useful for M\({}_{\rm w}\) or DP determinations in monitoring changes in cellulose in lignocellulosic materials. A comparison was made on the basis of results obtained with different detectors (MALS and/or UV-VIS) in analyses of various paper samples [37]; it included paper, a representative of typical lignin-containing acidic paper used in books of the 19 th and 20 th centuries. A high lignin content in paper samples that absorbs in the UV-VIS region [1] could interfere with M\({}_{\rm w}\) determinations of cellulose using SEC UV-VIS, making the approach unsuitable for the analysis of lignin-containing samples [11]. However, prior to SEC with UV-VIS detector, the CTC solutions are filtered with syringe filters, which remove most of the lignin [37]. The softwood paper samples show a bimodal distribution because the SEC UV-VIS system detects hemicelluloses with lower molecular mass than cellulose, while the MALS UV-VIS detector neglects the hemicellulose fraction. The results obtained with SEC UV-VIS were found to be reproducible, as demonstrated by the interlaboratory comparison between our laboratory and authors' laboratory [37]. The maximum relative error between the results for a large number of historical paper samples was 30% in the lower mass range, while the minimum error was 10% for the upper mass range. Using different data processing methods and SEC, it was again proved that molecular masses should be treated only relatively [37].